Conditional Execution - Building Java Programs: A Back to Basics Approach - page 227

4.1 if/else Statements

You will often find yourself writing code that you want to execute some of the time
but not all of the time. For example, if you are writing a game-playing program, you
might want to print a message each time the user achieves a new high score and store
that score. You can accomplish this by putting the required two lines of code inside
an if statement:

if (currentScore > maxScore) {
System.out.println("A new high score!");
maxScore = currentScore;

}

The idea is that you will sometimes want to execute the two lines of code inside the
if statement, but not always. The test in parentheses determines whether or not the
statements inside the if statement are executed. In other words, the test describes
the conditions under which we want to execute the code.
The general form of the if statement is as follows:

if (<test>) {
<statement>;
<statement>;
...
<statement>;

}

The if statement, like the for loop, is a control structure. Notice that we once
again see a Java keyword ( if ) followed by parentheses and a set of curly braces
enclosing a series of controlled statements.
The diagram in Figure 4.1 indicates the flow of control for the simple if state-
ment. The computer performs the test, and if it evaluates to true , the computer exe-
cutes the controlled statements. If the test evaluates to false , the computer skips the
controlled statements.

Ye s

Is the test true?

Execute the
controlled statement(s)

No

Execute the statement
after the if statement

Figure 4.1 Flow of if statement