Structuring Data with Java - Java - page 242

Solution

Define a class using < TypeName > where the container type is declared, and TypeName where
it is used.

Discussion

Consider the very simple Stack class in Example 7-2 . (We discuss the nature and uses of
stack classes in Stack ) .

This version has been parameterized to take a type whose local name is T . This type T will be
the type of the argument of the push() method, the return type of the pop() method, and so
on. Because of this return type—more specific than the Object return type of the original
Collections—the return value from pop() does not need to be downcasted. All containers in
the Collections Framework ( java.util ) are parameterized similarly.

Example 7-2. MyStack.java
public public class class MyStack MyStack < T > implements implements SimpleStack < T > {

private private int int depth = 0 ;

public public static static final final int int DEFAULT_INITIAL = 10 ;

private private T [] stack ;

public public MyStack () {

this

this ( DEFAULT_INITIAL );

}

public public MyStack ( int int howBig ) {

iif ( howBig <= 0 ) {
throw new IllegalArgumentException (

howBig + " must be positive, but was " + howBig );

throw new

}
stack = ( T []) new new Object [ howBig ];

}

@Override
public public boolean boolean empty () {

return

return depth == 0 ;

}

/** push - add an element onto the stack */
@Override
public public void void push ( T obj ) {