Inheritance - Data Structures and Problem Solving Using Java - page 153

1 public static <AnyType>
2 boolean contains( AnyType [ ] arr, AnyType x )
3 {
4 for( AnyType val : arr )
5 if( x.equals( val ) )
6 return true;
7
8 return false;
9 }

figure 4.34
Generic static method
to search an array

The generic method looks much like the generic class in that the type
parameter list uses the same syntax. The type parameters in a generic method
precede the return type.

4.7.4 type bounds

Suppose we want to write a findMax routine. Consider the code in Figure 4.35.
This code cannot work because the compiler cannot prove that the call to
compareTo at line 6 is valid; compareTo is guaranteed to exist only if AnyType is
Comparable . We can solve this problem by using a type bound . The type bound
is specified inside the angle brackets <> , and it specifies properties that the
parameter types must have. A naive attempt is to rewrite the signature as

The type bound is
specified inside the
angle brackets <> .

public static <AnyType extends Comparable> ...

This is naive because as we know, the Comparable interface is now generic.
Although this code would compile, a better attempt would be

public static <AnyType extends Comparable<AnyType>> ...

However, this attempt is not satisfactory. To see the problem, suppose
Shape implements Comparable<Shape> . Suppose Square extends Shape . Then all

figure 4.35
Generic static method
to find largest element
in an array that does
not work

1 public static <AnyType> AnyType findMax( AnyType [ ] a )
2 {
3 int maxIndex = 0;
4
5 for( int i = 1; i < a.length; i++ )
6 if( a[ i ].compareTo( a[ maxIndex ] ) > 0 )
7 maxIndex = i;
8
9 return a[ maxIndex ];
10 }