[Chapter 4] 4.11 Boolean Operators

4.11 Boolean Operators

The Boolean operators in Java are used for conditional AND (&&) and conditional OR (||) operations. These operators have different precedence; the && operator has the higher precedence and || the lower precedence. Both of the operators are evaluated from left to right.

The unary operator ! provides a Boolean negation operation.

References Boolean Negation Operator !; Order of Operations

Boolean AND Operator &&

The conditional AND operator && produces a pure boolean value that is the conditional AND of its operands. The && operator may appear in a conditional AND expression:

[Graphic: Figure from the text]

The conditional AND operator is evaluated from left to right. The operator never throws an exception.

Here is a code example that shows the use of the conditional AND operator:

public final short readShort() throws IOException {
    int ch1, ch2;
    if ((ch1 = in.read()) >= 0 && (ch2 = in.read()) >= 0)
        return (short)((ch1 << 8) + ch2);
    throw new EOFException();
}

The operands of the conditional AND operator must both be of type boolean, or a compile-time error occurs.

The operands of the conditional AND operator are evaluated in a different way from the operands for most other operators in Java. Most other operators evaluate all of their operands before performing their operation; the conditional AND operator does not necessarily evaluate both of its operands.

As with all binary operators, the left operand of && is evaluated first. If the left operand evaluates to true, the conditional AND operator evaluates its right operand and produces a pure value that has the same value as its right operand. However, if the left operand evaluates to false, the right operand is not evaluated and the operator produces the pure value false.

In the above example, the expression (ch2 = in.read()) is evaluated only if the expression (ch1 = in.read()) produces a value that is greater than or equal to zero.

References Bitwise/Logical AND Operator &; Boolean Type; Bitwise/Logical Inclusive OR Operator |; Order of Operations

Boolean OR Operator ||

The conditional OR operator || produces a pure boolean value that is the conditional OR of its operands. The || operator may appear in a conditional OR expression:

[Graphic: Figure from the text]

The conditional OR operator is evaluated from left to right. The operator never throws an exception.

Here is a code example that shows the use of the conditional OR operator:

public final short readShort() throws IOException {
    int ch1, ch2;
    if ((ch1 = in.read()) < 0 || (ch2 = in.read()) < 0)
        throw new EOFException();
    return (short)((ch1 << 8) + ch2);
}

The operands of the conditional OR operator must both be of type boolean, or a compile-time error occurs.

The operands of the conditional OR operator are evaluated in a different way from the operands for most other operators in Java. Most other operators evaluate all of their operands before performing their operation; the conditional OR operator does not necessarily evaluate both of its operands.

As with all binary operators, the left operand of || is evaluated first. If the left operand evaluates to false, the conditional OR operator evaluates its right operand and produces a pure value that has the same value as its right operand. However, if the left operand evaluates to true, the right operand is not evaluated and the operator produces the pure value true.

References Bitwise/Logical Inclusive OR Operator |; Boolean Type; Boolean AND Operator &&; Order of Operations