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Intro to Java

Input and Decision Statements

Most real-world Java programs do not simply execute a series of fixed instructions but need to dynamically react to user input. So far, we have mainly focused on the output (printing some text to the screen).

Example:

    System.out.println("Hello world!");

Input

In this chapter we focus on the input and processing parts of a program. To make our programs more interactive we will first learn how to read keyboard input from the user, presented in section Scanner.

Decision Statements

Depending on the users’ input the program can behave differently. This is a major concept in programming. This input dependent behaviour is called control flow.

In the section Decision Statements we learn how to write code that dynamically reacts to user input. This session focuses on decision statements, which are closely linked to boolean expressions (see 3 - Operators -> Exercise 2: Operators on boolean types). For example, we can tell our program that parts of the code shall only be executed if a boolean expression is true.

Example: if the shopping cart is empty, print “There are no items in your shopping cart!”

boolean shoppingCartIsEmpty = true;

if (shoppingCartIsEmpty) {
    System.out.println("There are no items in your shopping cart!");
}

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