Question 1

Given the following program, what will it do?

class Main {
 
 public static void main(String[] args) {
     System.out.println("Hello world!");
 }
}

• The program runs and Hello World! is printed to the console

• The program runs and nothing is printed to the console

• The program cannot run as it fails with a compile error

Solution for Question 1

When the program is ran, the main method is executed and thus Hello world! is printed to the console.
(Lesson 1)

Question 2

Given the following program, what will it do?

class Main {
 
 public static void main(String[] args) {

     // System.out.println("Hello Nr1")
     System.out.println("Hello Nr2");
     /*
     System.out.println("Hello Nr3")
     */
 }
}

• The program runs and first Hello Nr1 then Hello Nr2 then Hello Nr3 are printed to the console

• The program runs and first Hello Nr2 then Hello Nr3 are printed to the console

• The program runs and first Hello Nr1 then Hello Nr2 are printed to the console

• The program runs and Hello Nr2 is printed to the console

• The program cannot run as it fails with a compile error

Solution for Question 2

When the program is ran, Hello Nr2 is printed to the console. All other print statements are not executed as they are part of a comment!
(Lesson 1)

Question 3

Given the following program, how can we fix it so that it runs?

class Main {
 
}

 public static void main(String[] args) {
     System.out.println("Hello world!");
 }

• Nothing needs to be fixed, the program will run and print Hello World!

• The main method needs to be renamed to some other name

• The main method needs to be moved into the Main class

• The Main class needs to be renamed to some other name

Solution for Question 3

The main method needs to be moved into the Main class. Because in Java, a method can only be defined inside of a class.
(Lesson 1)

Question 4

Given the following program, how can we fix it so that it runs?

class Main {

 System.out.println("And Hello universe!");

 public static void main(String[] args) {
     System.out.println("Hello world!");
 }    
 
}

• Nothing needs to be fixed, the program will run and print Hello World!

• Nothing needs to be fixed, the program will run and print first Hello World! and then And Hello universe!

• Nothing needs to be fixed, the program will run and print first And Hello universe! and then Hello World!

• Remove the And Hello universe! print statement

• Move the And Hello universe! print statement into the main method

• The main method needs to be removed

Solution for Question 4

The first print statement (“And Hello universe!”) needs to be either removed or moved into the main method. Because in Java, any statement of code to be executed needs to be placed inside a method!
(Lesson 1)

Question 5

Given the following program, what will it do when we run it?

class Main {

 public static void mainFirst(String[] args) {
     System.out.println("Hello world!");
 } 

 public static void main(String[] args) {
     System.out.println("Hello other world!");
 }    
 
}

• It will print nothing

• The program will not run as it fails with an compile error

• It will print Hello other world!

• It will print Hello world!

Solution for Question 5

The program will only print Hello other world!. This is because a Java program always starts by executing the main method. It cannot print Hello world! as this print statement is inside the mainFirst method but mainFirst is never called from the main method.
(Lesson 1)

Question 6

Given the following program, what will it do when we run it?

class Main {

 public static void main(String[] args) {
     System.out.println("Hello world!");
 } 

 public static void main(String[] args) {
     System.out.println("Hello other world!");
 }     
 
}

• It will print nothing

• The program will not run as it fails with an compile error

• It will print Hello other world!

• It will print Hello world!

Solution for Question 6

The program will not compile: we have defined our main method with same parameters twice in the class which is not allowed in Java
(Lesson 1)

Question 7

Given the following program, what will it do when we run it?

class Main {

 public static void main1(String[] args) {
     System.out.println("Hello world!");
 } 

 public static void main2(String[] args) {
     System.out.println("Hello other world!");
 }     
 
}

• It will run and print nothing

• It will print Hello other world!

• It will print Hello world!

• The program will not run as it fails with an error

Solution for Question 7

The program can be compiled successfully. But when we then try to run it, it will fail with an error. This is due to the fact that we do not have a public static void main(String[] args) method defined in our program which is needed in any Java program as the entrypoint!
(Lesson 1)

Question 8

Given the following program, what will it do when we run it?

class First {

 public static void main(String[] args) {
     System.out.println("Hello world!");
 }      
 
}

class Second { 

 public static void main(String[] args) {
     System.out.println("Hello other world!");
 }     
 
}

• It will always print Hello other world!

• It will always print Hello world!

• It will print only Hello other world! if we try to run it as “java Second”

• It will print only Hello world! if we try to run it as “java First”

• The program will not compile if the Java file name is Main.java

Solution for Question 8

What the program does, depends firstly on the name of the source code file:

• If the name is First.java it will compile
• If the name is Second.java it will compile
• If the name is anything else it will not compile

Remember: a Java source code file needs to contain a class with the same name as the file

What the compiled program does depends on how we run it:

• if we run it with java First it will execute the main method of the First class and print Hello world!
• if we run it with java Second it will execute the main method of the Second class and print Hello other world!
  (Lesson 1)

Question 9

Given the following program, what will it do when we run it?

class Main {

 public static void main(String[] args) {
     System.out.println("Hello world!");
     Test.test1();
     Test.test2();
 }      
 
}

class Test { 

 public static void test1() {
     System.out.println("Hello other world 1!");
 }     
 
}

class Test { 

 public static void test2() {
     System.out.println("Hello other world 2!");
 }     
 
}

• The program will not compile and fail with an error

• It will print Hello world!

• It will print Hello other world 1!

• It will print Hello other world 2!

Solution for Question 9

The program will not compile as we have two classes with the same name in the same Java source code file!
(Lesson 1)

Question 10

Given the following program, what will it do?

class Main {
 
 public static void main(String[] args) {
     String text1;
     String text2 = "World";
     text1 = "Hello";
     text2 = "Everybody";
     System.out.println(text1);
     System.out.println(text2);
 }
}

• It will print Hello World

• It will print first Hello and then World in a new line

• It will print first Hello and then Everybody in a new line

• It will print first Everybody and then Hello in a new line

• It will not compile and fail with an error

Solution for Question 10

When the program is ran, it will first print Hello and then in a new line Everybody These are the values that are assigned to the variables text1 and text2 at the time the print statements are executed Note, that System.out.println jumps to a new line after printing.
(Lesson 2)

Question 11

Given the following program, what will it do?

class Main {
 
 public static void main(String[] args) {
     String text1;
     text2 = "World";
     text1 = "Hello";
     text2 = "Everybody";
     System.out.println(text1);
     System.out.println(text2);
 }
}

• It will print Hello World

• It will print first Hello and then World in a new line

• It will print first Hello and then Everybody in a new line

• It will print first Everybody and then Hello in a new line

• It will not compile and fail with an error

Solution for Question 11

We cannot run the program as it will not compile, i.e. we will get an error.
The reason is the second line of the main method.
We use the variable text2 for the first time but we did declare it by specifying what type it should have.
It should be: String text2 = “World”
(Lesson 2)

Question 12

Given the following program, what will it do?

class Main {
 
 public static void main(String[] args) {
     String text1;
     String text2 = "World";
     String text1 = "Hello";
     text2 = "Everybody";
     System.out.println(text1);
     System.out.println(text2);
 }
}

• It will print Hello World

• It will print first Hello and then World in a new line

• It will print first Hello and then Everybody in a new line

• It will print first Everybody and then Hello in a new line

• It will not compile and fail with an error

Solution for Question 12

We cannot run the program as it will not compile, i.e. we will get an error.
The reason is the third line of the main method.
We declare the variable text1 a second time here though it already exists in our program.
Note, that the declaration means we specify type and variable name!
(Lesson 2)

Question 13

Which of the assignments in the following program are valid?

class Main {
 
 public static void main(String[] args) {
     int i = 4.2;
     long l = 10.3;
     boolean b = 0;
     double d = 4;
     String s = 5;
 }
}

• All assignments are invalid

• The assignment to i is valid

• The assignment to l is valid

• The assignment to b is valid

• The assignment to d is valid

• The assignment to s is valid

Solution for Question 13

The only valid assignment is the assignment of d:

• i and l cannot be assigned a decimal value (int and long only represent numbers without decimals)
• b is a boolean and only has true and false as allowed values
• s is a String and can only be assigned a text (i.e. something surrounded with double quotes)
• d can take decimal values - but also the 4 as it can convert it (without loss of information) to a decimal (4.0)
  (Lesson 2)

Question 14

Which of the assignments in the following program are valid?

class Main {
 
 public static void main(String[] args) {
   int i = 1;
   long l = 1;
   float f = 1.0f;
   double d = 1.0;
   
   int h;
   h = i;
   h = l;
   h = f;
   h = d;
 }
}

• All assignments are invalid

• The assignment of i to h is valid

• The assignment of l to h is valid

• The assignment of f to h is valid

• The assignment of d to h is valid

Solution for Question 14

The only valid assignment is the assignment of i to h: h is an int and all other types may contain bigger values (i.e. values with more information) than an int can represent.
As Java does not allow an assignment that leads to a loss of information, these are all not allowed and lead to a compile error!
Note: in such assignments where the content of one variable is assigned to another, the actial value of the variable is not of importance - the types of both variables must allow the assignment (that’s why in our example, the assignment of l which is just 1 is also disallowed)
(Lesson 2)

Question 15

Which of the assignments in the following program are valid?

class Main {
 
 public static void main(String[] args) {
   int i = 1;
   long l = 1;
   float f = 1.0f;
   double d = 1.0;
   
   long h;
   h = i;
   h = l;
   h = f;
   h = d;
 }
}

• All assignments are invalid

• The assignment of i to h is valid

• The assignment of l to h is valid

• The assignment of f to h is valid

• The assignment of d to h is valid

Solution for Question 15

The valid assignments are i or l to h: h is an long and so decimal values cannot be assigned to it as decimal values may contain more information (i.e. the numbers after the decimal point) than a long can represent
i can be assigned to h as each value of an int can be represented by a long As Java does not allow an assignment that leads to a loss of information, these are all not allowed and lead to a compile error!
(Lesson 2)

Question 16

Which of the assignments in the following program are valid?

class Main {
 
 public static void main(String[] args) {
   int i = 1;
   long l = 1;
   float f = 1.0f;
   double d = 1.0;
   
   float h;
   h = i;
   h = l;
   h = f;
   h = d;
 }
}

• All assignments are invalid

• The assignment of i to h is valid

• The assignment of l to h is valid

• The assignment of f to h is valid

• The assignment of d to h is valid

Solution for Question 16

The only invalid assignment is of d to h h is an float and d a double and a double can contain bigger values (i.e. more information) than a float can represent As Java does not allow an assignment that leads to a loss of information, this is not allowed and lead to a compile error!
Any long or int can be assigned to a float (the decimal part just becomes .0)
(Lesson 2)

Question 17

Which of the assignments in the following program are valid?

class Main {
 
 public static void main(String[] args) {
   int i = 1;
   long l = 1;
   float f = 1.0f;
   double d = 1.0;
   
   double h;
   h = i;
   h = l;
   h = f;
   h = d;
 }
}

• All assignments are invalid

• The assignment of i to h is valid

• The assignment of l to h is valid

• The assignment of f to h is valid

• The assignment of d to h is valid

Solution for Question 17

All assignments are valid. h is a double and a double can contain any other primitive numerical value in Java
(Lesson 2)

Question 18

Given the following program, what will it print?

class Main {
 public static void main(String[] args) {
  int i1 = 5;
  int i2 = 2;
  double d1 = 5.0;
  double d2 = 2.0;

  System.out.println(i1 / i2);
  System.out.println(d1 / d2);
 }
}

• It will print 2 and 2

• It will print 2.5 and 2.5

• It will print 2 and 2.5

• It will print 2.0 and 2.5

• It will print 2.5 and 2

• It will print 2.5 and 2.0

Solution for Question 18

The program will print first 2 => we divide two int thus the result is also an int and for divisions of two int any leftover is omitted.
Then it will print 2.5 => we divide two double thus the result is also a double => thus we have a precise result of the division with the decimal value.
(Lesson 3)

Question 19

Given the following program, what will it print?

class Main {
 public static void main(String[] args) {
  int i1 = 5;
  int i2 = 2;
  double d1 = 5.0;
  double d2 = 2.0;

  System.out.println(i1 / d2);
  System.out.println(d1 / i2);
 }
}

• It will print 2 and 2

• It will print 2.5 and 2.5

• It will print 2 and 2.5

• It will print 2.0 and 2.5

• It will print 2.5 and 2

• It will print 2.5 and 2.0

Solution for Question 19

The program will print two times a 2.5
In both cases, we have a division of an int and an double. When applying an operator to two different types, Java will always use for the result the bigger type (i.e. the one that can hold more information). And in this case, it is double (remember that double is the most expressive numerical type in Java)
(Lesson 3)

Question 20

Given the following program, what will it print?

class Main {
 public static void main(String[] args) {
  int i1 = 5;
  int i2 = 2;
  double d1 = 5.0;
  double d2 = 2.0;

  double result1 = i1 / i2;
  double result2 = d1 / d2;

  System.out.println(result1);
  System.out.println(result2);
 }
}

• It will print 2 and 2

• It will print 2.5 and 2.5

• It will print 2 and 2.5

• It will print 2.0 and 2.5

• It will print 2.5 and 2

• It will print 2.5 and 2.0

Solution for Question 20

The program will print first 2.0 and then 2.5.
The 2.5 should be clear: we divide two double and assign the result to a double.
Let’s look what happens for the first result:

• first, a division of two int values happen => the result is just 2
• then, this result is assigned to a double variable => as this is a decimal number, the 2 is converted to be also a decimal number, i.e. 2.0
  (Lesson 3)

Question 21

Given the following program, which of the assignments are incorrect and lead to an error?

class Main {
 public static void main(String[] args) {
  int i1 = 5;
  int i2 = 2;
  double d1 = 5.0;
  double d2 = 2.0;

  int result1 = i1 / i2;
  int result2 = i1 / d2;
  int result3 = d1 / i2;
  int result4 = d1 / d2;

  System.out.println(result1);
  System.out.println(result2);
  System.out.println(result3);
  System.out.println(result4);
 }
}

• All assignments are valid

• The assignment to result1 is invalid

• The assignment to result2 is invalid

• The assignment to result3 is invalid

• The assignment to result4 is invalid

Solution for Question 21

The assignment to result1 is valid: division of i1 and i2 results in an int and can be assigned to an int variable.
All other assignments (to result2, result3, result4) are invalid: division results always in a double which cannot be assigned to an int
(Lesson 3)

Question 22

Given the following program, which change will make the program run without error and print a 2?

class Main {
 public static void main(String[] args) {
  int i = 5;
  double d = 2.0;

  int result = i / d;
  System.out.println(result);
 }
}

• int i = 5.0;

• double d = 2;

• int result = (int) i / d;

• int result = i / (int) d;

• int result = (double) i / d;

• int result = (int)(i / d);

Solution for Question 22

Let’s go through every answer:

• int i = 5.0; => this will not help but instead add an additional error (by trying to assign a double value to an int variable)
• double d = 2; => this would not change anything as d would still be a double (the value 2 would just be converted to 2.0)
• int result = (int) i / d; => this would not help as the casting is applied before division, i.e. this code will first cast i to an int (i.e. no change) and then divide by a double leading again to a double as result
• int result = i / (int) d; => this would work! The value d is casted to an int (which is allowed as we do it explicitely here) so the division becomes one of two int values resulting in an int as result!
• int result = (double) i / d; => this would not help as it will just cast i to a double and then divide by a double leading again to a double as result
• int result = (int)(i / d); => this would help! It still divides an int by a double resulting in a double. But then this resulting double is casted to an int (which is allowed as we do it explicitely here) and thus can be assigned to an int variable!
  (Lesson 3)

Question 23

Given the following program, what will it print?

class Main {
 public static void main(String[] args) {
  int i = 5;
  int j = 4;
  double d = 2.0;

  String result = "r=" + (i * j) + d + "!";
  System.out.println(result);
 }
}

• The program will not compile and fail with an error

• r=22!

• r=22.0!

• r=202!

• r=202.0!

• r=542.0!

Solution for Question 23

The correct answer is r=202.0!.
The first thing that is executed is the multiplication as it is enclosed by braces: 5 * 4 gives 20.
As there are no other braces, execution proceeds now from the left to the right.
First thing we see is a String, r= => thus all further + are interpreted as String concatenation!
(Lesson 3)

Question 24

Given the following program, what will it print?

class Main {
 public static void main(String[] args) {
  int i = 5;
  int j = 4;
  
  System.out.print(i >= 5 && j < 4);
  System.out.print(" ");
  System.out.print(i >= 5 || j < 4);
  System.out.print(" ");
  System.out.print(i < 6 && i > j);
  System.out.print(" ");
  System.out.print(i < 5 || j > i);
  System.out.print(" ");
  System.out.print(!(i >= 5 && j < 4));
 }
}

• It will print 5 times false

• It will print 5 times true

• false true true false true

• false true true false false

• true false false true false

Solution for Question 24

Remember:
The && condition is true if both conditions on its sides are true
The || condition is true if at least one condition of its both sides is true
The ! operator takes a boolean and switches it to its opposite (i.e. true to false, false to true)
(Lesson 3)

Question 25

Given the following program, what needs to be fixed so that it prints name and age of user?

class Main {
 public static void main(String[] args) {
  Scanner scanner = new Scanner();
  System.out.println("Enter your first name");
  String name = scanner.next();
  System.out.println("Enter your age");
  int age = scanner.next();
  
  System.out.println(name + " is " + age + " years old");
 }
}

• Add an import statement for Scanner class: import Scanner;

• Add an import statement for Scanner class: import java.util.Scanner;

• When creating Scanner, pass in System.in

• When creating Scanner, pass in System.out

• Read the name by using the nextLine() method

• Read the age by using the nextLine() method

• Read the age by using the nextInt() method

Solution for Question 25

Follow these rules when using Scanner to read input from the user:

• always remember the import statement import java.util.Scanner at the beginning of your file
• when creating a Scanner, pass in the System.in by doing new Scanner(System.in)
• use the right method to read input: next() reads a single word and returns it as String, nextLine() a complete line and returns that as String. For other types, use the corresponding method (e.g. nextInt(), nextDouble(), nextBoolean() etc)
  (Lesson 4)

Question 26

The following program will let the user enter his country and age but will immediately skip over the full name and will not wait for user to enter something. Which of the solutions could fix the problem?

import java.util.Scanner; 

class Main {
 public static void main(String[] args) {
  Scanner scanner = new Scanner(System.in);
  System.out.println("Enter your country of origin");
  String country = scanner.nextLine();
  System.out.println("Enter your age");
  int age = scanner.nextInt();
  System.out.println("Enter your full name");
  String fullName = scanner.nextLine();
  
  System.out.println(fullName + " is " + age + " years old and comes from " + country);
 }
}

• Change ‘String country = scanner.nextLine();’ to ‘String country = scanner.next();’

• Change ‘String fullName = scanner.nextLine();’ to ‘String fullName = scanner.next();’

• Read in the fullName before all other input

• Insert a new line with ‘scanner.nextLine();’ after ‘int age = scanner.nextInt();’

Solution for Question 26

The problem is due to how Scanner works internally => reread the part about Scanner in Lesson 4 for more details.
Let’s go through the answers:

• “Change String country = scanner.nextLine(); to String country = scanner.next();’” => will not change anything, our problem is with reading fullName
• “Change String fullName = scanner.nextLine(); to String fullName = scanner.next();” => this will allow us to enter something as full name => but it will end up only printing one word (the first name)
• “Read in the fullName before all other input” => this will fix the issue as the problem we have only happens if we use nextLine() directly after next() (or a corresponding method for another type)
• “Insert a new line with scanner.nextLine(); after int age = scanner.nextInt();” => this will also fix the problem - the additional scanner.nextLine() will clean the internal state of our Scanner that reading the fullName will work as epxected
  (Lesson 4)

Question 27

Given the following program, which statements about it are true?

import java.util.Scanner; 

class Main {
 public static void main(String[] args) {
  Scanner scanner = new Scanner(System.in);
  int number = scanner.nextInt();
  if(number > 10) {
    if(number > 100) {
      System.out.println("A");
    } 
    System.out.println("B");
  } else {
    if(number > 5) {
      System.out.println("C");
    } else {
      System.out.println("D");
    }
  }
 }
}

• Only ‘D’ is printed if the user enters 5

• ‘C’ is always printed if the user enters a number bigger than 5

• If the program prints ‘B’ it will always also print ‘A’

• If the program prints ‘A’ it will always also print ‘B’

Solution for Question 27

The program follows these rules:

• A is printed if the user enters a number bigger than 100
• B is printed if the user enters a number bigger than 10
• C is printed if the user enters 6, 7, 8, 9 or 10
• D is printed if the user enters 5 or a number smaller than 5
  (Lesson 4)

Question 28

Given the following program, which statements about it are true?

import java.util.Scanner; 

class Main {
 public static void main(String[] args) {
  Scanner scanner = new Scanner(System.in);
  int number = scanner.nextInt();
  if(number > 10) {
    System.out.println("B");
  } else if(number > 100) {
     System.out.println("A");
  } else if(number > 5) {
      System.out.println("C");
  } else {
     System.out.println("D");
  }
 }
}

• Only ‘D’ is printed if the user enters 5

• ‘C’ is always printed if the user enters a number bigger than 5

• If the program prints ‘B’ it will always also print ‘A’

• If the program prints ‘A’ it will always also print ‘B’

• ‘B’ is printed for a number bigger than 100

Solution for Question 28

The program follows these rules:

• A is never printed (as a number bigger than 100 is also bigger than 10)
• B is printed if the user enters a number bigger than 10
• C is printed if the user enters 6, 7, 8, 9 or 10
• D is printed if the user enters 5 or a number smaller than 5 (Lesson 4)

Question 29

Given the following program, which statements about it are true?

import java.util.Scanner; 

class Main {
 public static void main(String[] args) {
  Scanner scanner = new Scanner(System.in);
  int number = scanner.nextInt();
  if(number < 10) System.out.println("B");
  else if(number > 100) 
  System.out.println("A");
  else if(number > 50) System.out.println("C");
  else 
  System.out.println("D");
 }
}

• The program will not compile and fail with an error

• ‘D’ is printed if the user enters a 20

• ‘C’ is printed if the user enters a 80

• ‘B’ is printed if the user enters a 10

• It will print nothing for a number smaller zero

Solution for Question 29

The program follows these rules:

• A is printed if the user enters a number bigger than 100
• B is printed if the user enters a number smaller than 10
• C is printed if the user enters between 51 and 100
• D is printed if the user enters a number between 10 and 49

Note: if any if, else, else if is not followed by a block (i.e. curly braces) the next single statement is executed
(Lesson 4)

Question 30

Given the following program, which statements about it are true?

import java.util.Scanner; 

class Main {
 public static void main(String[] args) {
  Scanner scanner = new Scanner(System.in);
  int number = scanner.nextInt();
  if(number < 10) System.out.println("B");
  else if(number > 100); 
  System.out.println("A");
  if(number > 50) System.out.println("C");
  else 
  System.out.println("D");
 }
}

• The program will not compile with an error

• ‘D’ is printed if the user enters a 20

• ‘A’ is only printed if the user enters a number bigger than 100

• ‘B’ is printed if the user enters a 10

• It will print nothing for a number bigger 100

Solution for Question 30

The program follows these rules:

• A is printed always (note that there is a semicolon directly after the preceding else if => thus the printing of A is nit bound to any condition)
• B is printed if the user enters a number smaller than 10
• C is printed if the user enters bigger than 50
• D is printed if the user enters a number smaller or equal 50

Note: if any if, else, else if is not followed by a block (i.e. curly braces) the next single statement is executed
(Lesson 4)

Question 31

Given the following program, what will it print?

class Main {
 public static void main(String[] args) {
  int i = 10;
  for(i = 0; i < 5; i += 2) {
      System.out.println(i); 
  }
 }
}

• The program will not compile and fail with an error

• The program will print nothing

• The program will print 0, 1, 2, 3, 4

• The program will print 0, 2, 4

• The program will print 1, 3, 5

Solution for Question 31

It will print 0, 2 and 4.
Before the first iteration, i will be set to 0.
It will be then printed (i.e. the 0 as output).
Then i will be incremented by 2 and the next iteration happens - a 2 is printed.
Again, i is incremented by 2 and next iteration happens - a 4 is printed.
After the next increment by 2, i becomes bigger 5 => thus the loop will not be executed anymore.
(Lesson 5)

Question 32

Given the following program, what will it print?

class Main {
 public static void main(String[] args) {
  int i = 5;
  for(int j = i; j > 0; j--) {
      System.out.println(j); 
  }
 }
}

• The program will not compile and fail with an error

• The program will print nothing

• The program will print 1, 2, 3, 4, 5

• The program will print 5, 4, 3, 2, 1

• The program will print 5, 4, 3, 2, 1, 0

• The program will print 4, 3, 2, 1, 0

• The program will run forever printing always 5

Solution for Question 32

It will print 5, 4, 3, 2, 1.
Before the first iteration, j will be set to the value of i, i.e. 5.
After that j is printed in each iteration.
And j is decremented in each iteration. When j becomes 0, the loop stops.
Note: when a loop iteration ends, first the decrement happens and then the condition is checked (that’s why a 0 is not printed)
(Lesson 5)

Question 33

Given the following program, what will it print?

class Main {
 public static void main(String[] args) {
  int i = 5;
  for(int j = i; j > 0; i--) {
      System.out.println(j); 
  }
 }
}

• The program will not compile and fail with an error

• The program will print nothing

• The program will print 1, 2, 3, 4, 5

• The program will print 5, 4, 3, 2, 1

• The program will print 5, 4, 3, 2, 1, 0

• The program will print 4, 3, 2, 1, 0

• The program will run forever printing always 5

Solution for Question 33

The program will run forever printing 5.
The assignment of the value of i only happens before the first loop iteration.
Any changes to i later do have no effect on j => thus j never changes during the loop!
(Lesson 5)

Question 34

Given the following program, what will it print?

class Main {
 public static void main(String[] args) {
  int i = 5;
  for(int j = i; j < i; i--) {
      System.out.println(j); 
  }
 }
}

• The program will not compile and fail with an error

• The program will print nothing

• The program will print 1, 2, 3, 4, 5

• The program will print 5, 4, 3, 2, 1

• The program will print 5, 4, 3, 2, 1, 0

• The program will print 4, 3, 2, 1, 0

• The program will run forever printing always 5

Solution for Question 34

The program will end without printing anything.
The loop condition is false before the first iteration => thus the loop is never executed!
(Lesson 5)

Question 35

Given the following program, which of the following statements are correct?

import java.util.Scanner;

class Main {
 public static void main(String[] args) {
  Scanner scanner = new Scanner(System.in);
  int number = 0;
  while(number != 42) {
     number = scanner.nextInt();
     System.out.println(number);
  }
 }
}

• The program will always print a 0 as the first number

• If the user enters a 42, the program will end immediately without any further output

• The last number the program prints will always be 42

• The program may run forever

• The program may print nothing

Solution for Question 35

Let’s go through the statements:

• The program will always print a 0 as the first number => this is obviously not true, the first number printed will be the first number the user entered
• If the user enters a 42, the program will end immediately without any further output => this is false as the loop is executed at least once (number is initialized to 0 so the loop condition is initially true) and the loop body contains as last statement the printing of the number so each number the user enters must be printed
• The last number the program prints will always be 42 => this is correct. The program ends when the user enters a 42 (number becomes 42). This is printed before the loop ends - so the last printed number must be 42
• The program may run forever => this is true, the program will run forever if the user never enters 42
• The program will print nothing => this is false, as there is no way that the program will print nothing!
  (Lesson 5)

Question 36

Given the following program, which of the following statements are correct?

import java.util.Scanner;

class Main {
 public static void main(String[] args) {
  Scanner scanner = new Scanner(System.in);
  int number = scanner.nextInt();;
  while(number != 42) {
     System.out.println(number);
     number = scanner.nextInt();
  }
 }
}

• The program will always print a 0 as the first number

• If the user enters a 42, the program will end immediately without any further output

• The last number the program prints will always be 42

• The program may run forever

• The program may print nothing

Solution for Question 36

Let’s go through the statements:

• The program will always print a 0 as the first number => this is obviously not true, the first number printed will be the first number the user entered
• If the user enters a 42, the program will end immediately without any further output => this is true as anytime the user enters a number, the next action is the check of the loop condition. As the loop condition becomes false when number is 42, the print statement would not be executed
• The last number the program prints will always be 42 => this is false as the loop would in this case end before any further print statement
• The program may run forever => this is true, the program will run forever if the user never enters 42
• The program may print nothing => this is true, it could happen if the user enters 42 as the first number
  (Lesson 5)

Question 37

Given the following program, what will it print?

class Main {
 public static void main(String[] args) {
  System.out.println("A");
  second();
  System.out.println("B");
  System.out.println("C");
  first();
 }

 public static void first() {
   System.out.println("D");
 }

 public static void second() {
   System.out.println("E");
 }

}

• The program will not compile and fail with an error

• The program will print A, B, C

• The program will print A, B, C, D, E

• The program will print D, E, A, B, C

• The program will print E, D, A, B, C

• The program will print A, D, B, C, E

• The program will print A, E, B, C, D

Solution for Question 37

It will print A, E, B, C, D.
It will start in main and executes the first print statement so A is printed.
It will then call method second and execute the statement in it, so E is printed.
It will then continue in main so B and C are printed.
It will then call method first and execute the statement in it, so D is printed.
(Lesson 6)

Question 38

Given the following program, what will it print?

class Main {
 public static void main(String[] args) {
  System.out.println("A");
  int n = 22;
  test(2, "B");
  test(n, "C");
  String text = "D";
  n = 1;
  test(n, "E");
  test(33, "Y");
 }

 public static void test(int n, String text) {
   if(n > 5) {
      System.out.println("Z");
   } else {
      System.out.println(text);
   }
 }

}

• The program will not compile and fail with an error

• The program will print A, B, Z, E, Z

• The program will print A, Z, Z, E, Z

• The program will print A, B, C, E, Y

• The program will print A, B, Z, D, Z

• The program will print A, B, Z, D, Y

Solution for Question 38

It will print A, B, Z, E, Z.
It will start in main and executes the first print statement so A is printed.
It will then call method test with parameters 2 and B - so when we execute test then n in test is 2 and text in test is B => so we print B.
It will then call method test with parameters n (i.e. the current value of n in main which is 22) and C - so when we execute test then n in test is 22 and text in test is C => so we print Z. It will then call method test with parameters n (i.e. the current value of n in main which has changed to 1__) and _E - so when we execute test then n in test is 1 and text in test is E => so we print E.
It will then call method test with parameters 33 and Y - so when we execute test then n in test is 33 and text in test is Y => so we print Z.
(Lesson 6)

Question 39

Given the following program, what will it print?

class Main {
 public static void main(String[] args) {
  System.out.println("A");
  int n = test(2, "B");
  int z = test(n, "C");
  System.out.println(z);
  n = test(n * z, "K");
  System.out.println(n);
 }

 public static int test(int n, String text) {
   if(n > 5) {
      System.out.println("Z");
   } else {
      System.out.println(text);
   }
   int r = n + 1;

   return r;
 }

}

• The program will not compile and fail with an error

• The program will print A, B, Z, 1, Z, 1

• The program will print A, B, C, 3, Z, 6

• The program will print A, B, C, 4, Z, 13

• The program will print A, B, C, 2, Z, 2

Solution for Question 39

It will print A, B, C, 4, Z, 13.
It will start in main and executes the first print statement so A is printed.
It will then call method test with parameters 2 and B - so when we execute test then n in test is 2 and text in test is B => so we print B. Also we return 3. In main, we set n to that value- It will then call method test with parameters n (i.e. the current value of n in main which is 3) and C - so when we execute test then n in test is 3 and text in test is C => so we print C. We return now 4. In main, we set z to 4
We now print z i.e. we print 4.
It will then call method test with parameters n * z (i.e. the current value of n times the current value of z in main which is 3 * 4, i.e. 12) and K - so when we execute test then n in test is 12 and text in test is K => so we print Z. We return now 13 and set n to that value in main.
In main, we print now the current value of n, i.e. we print 13.
(Lesson 6)

Question 40

Given the following program, what will it print?

class Main {
 public static void main(String[] args) {
  System.out.println("A");
  int n = test(2, "B");
  int z = test(n, "C");
  System.out.println(z);
  n = test(n * z, "K");
  System.out.println(n);
 }

 public static int test(int n, String text) {
   if(n > 5) {
      System.out.println("Z");
      return (n + 1);
   } else {
      System.out.println(text);
   }
 }

}

• The program will not compile and fail with an error

• The program will print A, B, Z, 1, Z, 1

• The program will print A, B, C, 3, Z, 6

• The program will print A, B, C, 4, Z, 13

• The program will print A, B, C, 2, Z, 2

Solution for Question 40

The program will not compile and will fail with an error.
The problem is in the test method - it declares a return type int - but we only have a return statement in the if but no return in the else.
If a method in Java has a return type, we must ensure that we return a value in each case!
(Lesson 6)

Question 41

Given the following program, what will it print?

class Main {
 public static void main(String[] args) {
  System.out.println("A");
  int n = test("B", 2);
  String z = test(n, "C");
  System.out.println(z);
  n = test(n * 12);
  System.out.println(n);
 }

 public static int test(int n, String text) {
   if(n > 5) {
      System.out.println("Z");
   } else {
      System.out.println(text);
   }
   return (n + 1);
 }

}

• The program will not compile and fail with an error

• The program will print A, B, Z, 1, Z, 1

• The program will print A, B, C, 3, Z, 6

• The program will print A, B, C, 4, Z, 13

• The program will print A, B, C, 2, Z, 2

Solution for Question 41

The program will not compile and will fail with an error.
All calls to test have a problem:

• the first call to test has the parameters switched - it calls with a String on first position and an int on second => but the test method expects an int as first parameter and a String as second
• the second call to test fail to handle the returned value correctly - it tries to assign it to a String variable. But the return type of test is declared to be an int
• the third call to test misses one parameter
  (Lesson 6)

Question 42

Given the following program, what will it print?

class Main {
 public static void main(String[] args) {
  System.out.println("A");
  int n = test(2, "B");
  int z = test(n, "C");
  System.out.println(z);
  n = test(n * z,"E");
  System.out.println(n);
 }

 public static int test(int n, String text) {
   if(n > 5 || z > 0) {
      System.out.println("Z");
   } else {
      System.out.println(text);
   }
   return (n + 1);
 }

}

• The program will not compile and fail with an error

• The program will print A, B, Z, 1, Z, 1

• The program will print A, B, C, 3, Z, 6

• The program will print A, B, C, 4, Z, 13

• The program will print A, B, C, 2, Z, 2

Solution for Question 42

The program will not compile and will fail with an error.
The problem is that the test method tries to access a variable z. But z is only defined in main and thus is also accessible inside main (i.e. inside the scope of the method main). The only way to give test access to value of z would be to pass it as a parameter to test! (Lesson 6)

Question 43

Given the following program, what will it print?

class Main {
 public static void main(String[] args) {
   String text = "abrakadabrasimsalabim";
   String sub = "ab";
   int count = 0;
   int i = text.indexOf(sub);
   while(i != -1) {
     count++;
     text = text.substring(i + sub.length());
     i = text.indexOf(sub);
   }
   System.out.println(count);
   System.out.println(text);
 }

}

• The program will not compile and fail with an error

• The program will print 0 and abrakadabrasimsalabim

• The program will print 3 and abrakadabrasimsalabim

• The program will print 1 and rakadabrasimsalabim

• The program will print 1 and rakadrasimsalim

• The program will print 3 and rakadrasimsalim

• The program will print 3 and im

Solution for Question 43

The program will print 3 and im - here is why: The program counts the appearance of the value of variable sub in variable text by using indexOf (this will return the position in the string where the value appears or -1 if not found - thus the loop will run 3 times and count will be 3 at the end).
Additionally, every time the term is found, text is updated to only keep the part of the string after the found term.
Thus at the end, text will have the value everything after the last appereance of sub , i.e. im! (Lesson 7)

Question 44

Given the following program, which of the statements is true?

import java.util.Scanner;

class Main {
 public static void main(String[] args) {
   Scanner scanner = new Scanner(System.in);
   String word = scanner.next().toLowerCase();

   String result = "";
   for(int i = word.length(); i > 0; i--) {
     if(valid(word.charAt(i - 1))) {
       result = result + word.charAt(i - 1);
     }
   }
   System.out.println(result);
 }

 public static boolean valid(char c) {
   return c != 'a' && c != 'e' && c != 'i' && c != 'o' && c != 'u';
 }
}

• The program will not compile and fail with an error

• The program will print one word containing no vowels

• The program will print one word where characters are in same order as entered

• The program will print only capital letters

• Given the input ‘HEllO’, the program will print ‘llh’

Solution for Question 44

The program will first turn the input to lower case letters.
It will then process the characters of the word in reverse order and filter out all vowels.
So the printed word will be all consonants of the entered word in reversed order and lower case!
(Lesson 7)

Question 45

Given the following program, what will it print?

class Main {
 public static void main(String[] args) {
   String s1 = "hello";
   String s2 = "Hello";

   boolean b1 = s1 == s2;
   boolean b2 = s1 == (s2.toLowerCase());
   boolean b3 = s1.equals(s2);
   boolean b4 = s1.equals(s2.toLowerCase());
   boolean b5 = s1.toUpperCase().equals(s2);
   boolean b6 = s1.equalsIgnoreCase(s2);
   boolean b7 = s1.toUpperCase().equalsIgnoreCase(s2);

   System.out.println(b1);
   System.out.println(b2);
   System.out.println(b3);
   System.out.println(b4);
   System.out.println(b5);
   System.out.println(b6);
   System.out.println(b7);
 }
}

• The program will not compile and fail with an error

• The program will print 7 times_true_

• The program will print 7 times_false_

• The program will print false true false true false true true

• The program will print false false false true false true true

• The program will print false false false false true true true

Solution for Question 45

The program will print false false false true false true true.
The checks using the == operator will anyway return false as they do not check the content of the String for equality but just if it the same object.
The equals method is case-sensitive so it will only return true when s2 is changed to lower cases (so the result is equal to s1).
The equalsIgnoreCase is not case-sensitive so it will return true as long as both strings contains the same letters (no matter if in upper or lower cases)
(Lesson 7)

Question 46

Given the following program, which of the statements are true?

import java.util.Scanner;

class Main {
 public static void main(String[] args) {
   Scanner scanner = new Scanner(System.in);
   String text = scanner.nextLine();

   if(text.startsWith("a") && text.endsWith("b")) {
     System.out.println(text.replace("c", "d"));
   }
   System.out.println(text);
 }
}

• The program will not compile and fail with an error

• The program will always print the text exactly as the user has entered it

• The program will only print the text exactly as the user has entered it if it did not start with an ‘a’ or did not end with an ‘b’ or did not contain a ‘c’

• The program will print the entered text with each ‘c’ replaced by a ‘d’ if it started with ‘a’ and ended with ‘b’

• The program will print the entered text with each ‘d’ replaced by a ‘c’ if it started with ‘a’ and ended with ‘b’

Solution for Question 46

The program will at the end always print the text as the user has entered it.
Note that the replace method does not change the String on that it is called - it creates a new copy of that where the replacements has happened, so text itself is never changed.
Additionally the program prints a version of text where each c is replaced by a d if text starts with a and ends with b.
(Lesson 7)

Question 47

Given the following program, what will it print?

import java.util.ArrayList;

class Main {
 public static void main(String[] args) {
   ArrayList<String> words = new ArrayList<String>();
   words.add("1");
   words.add("2");
   words.add(3);
   System.out.println(words); 
 }
}

• The program will not compile and fail with an error

• The program will print ‘[“1”,”2”,3]’

• The program will print ‘[1,2,3]’

• The program will print ‘[“1”,”2”,”3”]’

Solution for Question 47

The program will not compile and fail with an error.
If you use an ArrayList you can specify what should be the type of elements that it should contain:

• e.g. ArrayList<Integer> tells that the list can only contain integer values
• e.g. ArrayList<String> tells that the list can only contain integer values Thus you
• cannot add a value of a different type to such a list
• need to assign a value you get from the list to a variable of the correct type If you do not follow these rules, your program will fail to compile (Lesson 8)

Question 48

Given the following program, which of the statements are true?

import java.util.ArrayList;

class Main {
 public static void main(String[] args) {
   ArrayList<String> words = new ArrayList<String>();
   words.add("a");
   words.add("b");
   words.add("c");
   words.add("d");
   words.add("e");
   words.add("f");
   words.add("j");

   for(int i = 0; i < words.size(); i = i + 2) {
     System.out.println(words.get(i + 1));
   }
 }
}

• The program will print ‘a’, ‘c’, ‘e’, ‘j’

• The program will print ‘a’, ‘c’, ‘e’

• The program will print ‘b’, ‘d’, ‘f’

• The program will print ‘b’, ‘d’, ‘f’, ‘j’

• The program will fail with an error after printing the last character

• The program will end without any error

Solution for Question 48

The program will start by printing every second element in the list (i.e. b, d, f).
After it printed f, the value of i is 4. The loop will then increment i to 6.
Another loop iteration is executed as i is smaller than the size of the list (the number of elements in the list) which is 7.
Now inside the loop, it is tried to print the list element at index 7.
Note that the indices of a list start at index 0, so valid indices for the given list are from 0 to 6. 7 is too big and so the program fails! (Lesson 8)

Question 49

Given the following program, what will it do?

import java.util.ArrayList;

class Main {
 public static void main(String[] args) {
   ArrayList<String> words = new ArrayList<String>();
   words.add("a");
   words.add("b");
   words.add("c");

   for(int i = 0; i < words.size(); i++) {
     System.out.println(words.get(i));
   }

   for(String word : words) {
     System.out.println(words);
   }
 }
}

• The program will not compile and fail with an error

• The first loop will print ‘a’ and ‘b’ and the second loop ‘a’, ‘b’ and ‘c’

• Both loops do exactly the same and print both ‘a’, ‘b’ and ‘c’

• The first loop will print ‘a’, ‘b’ and ‘c’ while the second will print in one line ‘[a,b,c]’

Solution for Question 49

Both loops do exactly the same and print each element in the list.
Note that the for each loop is a shorter syntax for accessing every element in the loop (in each iteration, the loop variable , here word is set to the next element of the list). (Lesson 8)

Question 50

Given the following program, what will it print?

import java.util.ArrayList;

class Main {
 public static void main(String[] args) {
   ArrayList<String> words = new ArrayList<String>();
   words.add("a");
   words.add("b");
   words.add("c");
   words.add("d");
   
   test(words);
   System.out.println(words.toString());

   words.add("e");
   test(words);
   System.out.println(words.toString());
 }

 public static void test(ArrayList<String> _list) {
   for(int i = 0; i < _list.size() / 2; i++) {
     int h = _list.size() - i - 1;
     String t = _list.get(i);
     _list.set(i, _list.get(h));
     _list.set(h, t);
   }
 }
}

• The program will fail with an error

• The program will print ‘[d, c, b, a]’ and ‘[e, a, b, c, d]’

• The program will print ‘[d, c, b, a]’ and ‘[e, d, c, b, a]’

• The program will print ‘[b, a, d, c]’ and ‘[a, b, c, e, d]’

Solution for Question 50

The program will print [d, c, b, a] and [e, a, b, c, d] .
The test basically swaps the elements in the list in the following way:

• first element is swapped with the last element
• second element is swapped with second last element
• and so on … Note: the set element changes the given list directly! (Lesson 8)

Question 51

Given the following program, what will it print?

import java.util.ArrayList;

class Main {
 public static void main(String[] args) {
   ArrayList<String> words = new ArrayList<String>();
   words.add("a");
   words.add("b");
   words.add("c");
   words.add("c");
   words.add("b");
   words.add("a");
   
   test(words, "b");
   System.out.println(words.toString());
 }

 public static void test(ArrayList<String> _list, String s) {
   boolean running = true;
   while(running) {
    int idx = _list.indexOf(s);
     if(idx == -1) {
       running = false;
     } else {
       _list.remove(idx);
     }
   }
 }
}

• The program will fail with an error

• The program will print ‘[b, b]’

• The program will print ‘[a, c, c, b, a]’

• The program will print ‘[a, c, c, a]’

Solution for Question 51

The program will print [a, c, c, a].
The test basically removes all occurrences of the given String in the given list.
It uses indexOf to get the index of the next appearance of the string in the list - if it is -1, the list does not contain anymore the string so the loop ends, else the element at that index is deleted. Note: the remove element changes the given list directly! (Lesson 8)

Question 52

Given the following program, what will it print?

import java.util.ArrayList;

class Main {
 public static void main(String[] args) {
   ArrayList<String> words = new ArrayList<String>();
   words.add("a");
   words.add("b");
   words.add("c");
   words.add("d");
   words.add("e");
   words.add("f");
   
   int i1 = 1;
   int i2 = 3;

   String s = words.get(i1);
   words.remove(i1);
   words.add(i2, s);
   System.out.println(words);
 }
}

• The program will fail with an error

• The program will print ‘[a, c, d, b, e, f]’

• The program will print ‘[b, c, a, d, e, f]’

• The program will print ‘[a, c, b, d, e, f]’

• The program will print ‘[a, c, d, e, b, f]’

Solution for Question 52

The program will print [a, c, d, b, e, f].
It will first assign the element at index 1 to s , i.e. s becomes b.
It will then remove the element at index 1 so words will become [a, c, d, e, f]. It will then add b at index 3 (i.e. add as 4th element into the list) so words will finally become [a, c, d, b, e, f]. (Lesson 8)

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