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Relational and Conditional Operators

A relational operator compares two values and determines the relationship between them. For example, != returns true if the two operands are unequal. This table summarizes Java's relational operators:

Operator	Use	Returns true if
>	op1 > op2	op1 is greater than op2
>=	op1 >= op2	op1 is greater than or equal to op2
<	op1 < op2	op1 is less than op2
<=	op1 <= op2	op1 is less than or equal to op2
==	op1 == op2	op1 and op2 are equal
!=	op1 != op2	op1 and op2 are not equal

Relational operators often are used with the conditional operators to construct more complex decision-making expressions. One such operator is &&, which performs the boolean and operation. For example, you can use two different relational operators along with && to determine if both relationships are true. The following line of code uses this technique to determine if an array index is between two boundaries. It determines if the index is both greater than 0 and less than NUM_ENTRIES (which is a previously defined constant value):

0 < index && index < NUM_ENTRIES

Note that in some instances, the second operand to a conditional operator may not be evaluated. Consider this code segment:

(numChars < LIMIT) && (...)

The && operator will return true only if both operands are true. So, if numChars is greater than LIMIT, the left-hand operand for && is false and the return value of && can be determined without evaluating the right-hand operand. In such a case, Java will not evaluate the right-hand operand. This has important implications if the right-hand operand has side effects such as reading from a stream, updating a value, or making a calculation.

The operator & is similar to && if both of its operands are of boolean type. However, & always evaluates both of its operands and returns true if both are true. Likewise, | is similar to || if both of its operands are boolean. This operator always evalutes both of its operands and returns false if they are both false.

Java supports five binary and one unary conditional operators, shown in the following table:

Operator	Use	Returns true if
&&	op1 && op2	op1 and op2 are both true, conditionally evaluates op2
||	op1 || op2	either op1 or op2 is true, conditionally evaluates op2
!	! op	op is false
&	op1 & op2	op1 and op2 are both true, always evaluates op1 and op2
|	op1 | op2	either op1 or op2 is true, always evaluates op1 and op2
^	op1 ^ op2	if op1 and op2 are different--that is if one or the other of the operands is true but not both

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