容器類常用方法（4）_适配

1. Iterable接口： 實作這個接口允許對象成為 "foreach" 語句的目标；Collection實作了此接口

2. ArrayList實作了Iterable接口，提供了用foreach正向疊代的能力，現在需要增加一個反向疊代的能力，實作代碼如下：

   a)用到了擴充卡模式

package context;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Iterator;

public class ReverseArrayList<T> extends ArrayList<T> {
	
	private static final long serialVersionUID = 1L;

	public static void main(String[] args) {
		ReverseArrayList<String> list = new ReverseArrayList<String>(Arrays.asList("you are a pig ?".split(" ")));
		//此處将list向上轉型為Iterable
		for(String str : list) {  //(Iterable<String>list)
			System.out.print(str + " ");
		}
		System.out.println();
		
		for(String str : list.reversed()) {
			System.out.print(str + " ");
		}
		System.out.println();
	}
	
	public ReverseArrayList(Collection<T> c) {
		super(c);
	}
		
	public Iterable<T> reversed() {
		return new Iterable<T>() {
			@Override
			public Iterator<T> iterator() {
				return new Iterator<T>() {
					int current = size() -1;
					@Override
					public boolean hasNext() {
						return current > -1;
					}
					@Override
					public T next() {
						return get(current--);
					}
					@Override
					public void remove() {
						throw new RuntimeException();
					}
					
				};
			}
			
		};
	}
	
}
           

//output
you are a pig ? 
? pig a are you