Java Reference
In-Depth Information
flags |= f ; // Set a flag f in an integer set of flags
flags &= ~ f ; // Clear a flag f in an integer set of flags
The Conditional Operator
The conditional operator ? : is a somewhat obscure ternary (three-operand) opera‐
tor inherited from C. It allows you to embed a conditional within an expression.
You can think of it as the operator version of the if/else statement. The first and
second operands of the conditional operator are separated by a question mark ( ? )
while the second and third operands are separated by a colon (:). The first operand
must evaluate to a boolean value. The second and third operands can be of any
type, but they must be convertible to the same type.
The conditional operator starts by evaluating its first operand. If it is true , the oper‐
ator evaluates its second operand and uses that as the value of the expression. On
the other hand, if the first operand is false , the conditional operator evaluates and
returns its third operand. The conditional operator never evaluates both its second
and third operand, so be careful when using expressions with side effects with this
operator. Examples of this operator are:
int max = ( x > y ) ? x : y ;
String name = ( name != null ) ? name : "unknown" ;
Note that the ? : operator has lower precedence than all other operators except the
assignment operators, so parentheses are not usually necessary around the operands
of this operator. Many programmers find conditional expressions easier to read if
the first operand is placed within parentheses, however. This is especially true
because the conditional if statement always has its conditional expression written
within parentheses.
The instanceof Operator
The instanceof operator is intimately bound up with objects and the operation of
the Java type system. If this is your first look at Java, it may be preferable to skim
this definition and return to this section after you have a decent grasp of Java's
instanceof requires an object or array value as its left operand and the name of a
reference type as its right operand. It evaluates to true if the object or array is an
instance of the specified type; it returns false otherwise. If the left operand is null ,
instanceof always evaluates to false . If an instanceof expression evaluates to
true , it means that you can safely cast and assign the left operand to a variable of
the type of the right operand.
The instanceof operator can be used only with reference types and objects, not
primitive types and values. Examples of instanceof are:
// True: all strings are instances of String
"string" instanceof String
// True: strings are also instances of Object
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