The boolean type

The boolean is a primitive data type that has only two possible values: false or true. The default value for this type is false.

    boolean t = true; // t is true
    boolean f = false; // f is false
    boolean defaultValue; // defaultValue is false

Note: Remember, you cannot assign an integer value to a boolean variable. In Java, 0 is not equal to false.

Logical operators

There are four logical operators NOT, AND, OR and XOR which allow us to build logical expressions.

The NOT operator is a unary operator that reverses the boolean value. It is written as !.

    boolean f = false; // f is false
    boolean t = !f; // t is true

The AND operator is a binary operator that returns true if both operands are true, otherwise, it is false. The operator can be written as && and &.

    boolean b1 = false && false; // false
    boolean b2 = false && true; // false
    boolean b3 = true && false; // false
    boolean b4 = true && true; // true

The OR operator is a binary operator that returns true if at least one operand is true, otherwise, it returns false. The operator can be written as ||and |.

    boolean b1 = false || false; // false
    boolean b2 = false || true; // true
    boolean b3 = true || false; // true
    boolean b4 = true || true; // true

The XOR (exclusive OR) operator is a binary operator that returns true if boolean operands have different values, otherwise, it is false. The operator is written as ^ and can be used Instead of the relation operator != (NOT EQUAL TO).

    boolean b1 = false ^ false; // false
    boolean b2 = false ^ true; // true
    boolean b3 = true ^ false; // true
    boolean b4 = true ^ true; // false

Short-circuit operators

The AND and OR operators have two forms: AND ( &, &&), OR ( |, ||).

There are some differences:

• the & and | operators are also used as bitwise operators for integer types;
• the && and || operator perform Conditional-AND and Conditional-OR operations on two boolean expressions. These operators are called "short-circuit" operators, which means that the second operand is evaluated only when it is needed (when the first argument doesn't suffice to determine the value of the expression).

In the following example, the second operand a>5 will not be evaluated because the result is determined by the first operand (a==10 is false):

    int a = 20;
    boolean result = (a == 10) && (a > 5); // the second expressions can't be evaluated

The precedence of logical operators

Below the logical operations are sorted in order of their priority in expressions:

1. ! - NOT
2. & - AND
3. ^ - XOR
4. | - OR
5. && - conditional AND
6. || - conditional OR

So, the following statement is true:

    boolean b = true && !false; 
    // true, because !false is evaluated first