wildcardbound.java

Java面向对象编程(随书配套源代码) 阐述了面向对象编程的思想

package chapter11;
import java.util.*;
import chapter7.*;
public class WildcardBound 
{
	public static boolean isEmpty( Stack<? extends List> s  )
	{
		return s.isEmpty();
	}
	public static boolean isEmpty2(Stack2<? super Duck> s)
	{
		return s.isEmpty();
	}
	public static void main(String args[])
	{
		Stack<List> lsStack = new  Stack<List>(10);
		Stack<String> strStack = new Stack<String>(10);
		Stack2<Animal> animalStack = new Stack2<Animal>(10); 
		Stack2<Duck> duckStack = new Stack2<Duck>(10); 
		Stack2<Wolf> wolfStack = new Stack2<Wolf>(10); 
		
		//WildcardBound.isEmpty(strStack); //WildcardBound类型中的方法isEmpty( Stack<? extends List> s  )对于参数Stack<String>不适用
		WildcardBound.isEmpty(lsStack); 
		WildcardBound.isEmpty2(animalStack);
		WildcardBound.isEmpty2(duckStack);
		//WildcardBound.isEmpty2(wolfStack);
	}
}