6.5 The if Statement

An if statement determines which of two statements is executed, based on the value of a Boolean expression:

In Java, the expression in parentheses must produce a boolean value. This is different from C/C++, which allows any type of expression.

If the expression in parentheses evaluates to true, the statement after the parentheses is executed. After that statement has been executed, the statement following the entire if statement is executed. If the expression between the parentheses evaluates to false, the next statement to be executed depends on whether or not the if statement has an else clause. If there is an else clause, the statement after the else is executed. Otherwise, the statement after the entire if statement is executed.

When if statements are nested, each else clause is matched with the last preceding if statement in the same block that has not yet been matched with an if statement.

Here is an example of an if statement:

if (j == 4) {
    if (x > 0 ) {
        x *= 7;
    } else {
        x *= -7;
    }
}
return;

The outer if statement has no else clause. If j is not 4, the return statement is executed. Otherwise, the inner if statement is executed. This if statement does have an else clause. If x is greater than zero, the value of x is multiplied by 7. Otherwise, the value of x is multiplied by -7. Regardless of the value of x, the return statement is executed.

References Boolean Type; Expression 4; Statement 6