Boolean decisions

A boolean variable can hold one of two values: true or false. A boolean expression is an expression that can return one of two values: true or false.

Boolean expressions are often used when making decisions. This means you'll want to be comfortable using boolean expressions in if-statements. To do this, you test the value of an expression. You can use that value to determine where your program goes.

Example:

System.out.print("Enter your test score: ");
        int score = scan.nextInt();
        char grade = 'F';//I'm not hopeful

        if (score > 89)
            grade = 'A';
        else if (score > 79)
            grade = 'B';
        else if (score > 69)
            grade = 'C';
        else 
            grade = 'F';

        if (score > 69)
            System.out.println("Very good! You don't have to retake the exam!");
        else
            System.out.println("Did you even look at the book?");

Saying No!

You can negate a boolean expression with the ! operator.

Legal boolean expressions

In an if-statement the legal expression is a boolean. Some programming languages allow you to use 1 for true or 0 for false. Not Java. Java requires an expression which evaluates to true or false. if (1) is not legal but if (1==1) is legal.

An example

if (x > 3) {
    System.out.println("x is greater than 3");
}else{
    System.out.println("x is less than or equal to 3");
}