浅谈关于collection接口及相关容器类（一）

Collection在英文单词的意思是：採集，收集。

而在JAVA API 文档中它是一个收集数据对象的容器。

Collection作为容器类的根接口。例如以下图（部分子接口未写出）：

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文档中说明了Collection接口，有例如以下的方法：

boolean	add(E e) Ensures that this collection contains the specified element (optional operation).
boolean	addAll(Collection<? extendsE> c) Adds all of the elements in the specified collection to this collection (optional operation).
void	clear() Removes all of the elements from this collection (optional operation).
boolean	contains(Object o) Returns true if this collection contains the specified element.
boolean	containsAll(Collection<?> c) Returns true if this collection contains all of the elements in the specified collection.
boolean	equals(Object o) Compares the specified object with this collection for equality.
int	hashCode() Returns the hash code value for this collection.
boolean	isEmpty() Returns true if this collection contains no elements.
Iterator<E>	iterator() Returns an iterator over the elements in this collection.
boolean	remove(Object o) Removes a single instance of the specified element from this collection, if it is present (optional operation).
boolean	removeAll(Collection<?> c) Removes all of this collection's elements that are also contained in the specified collection (optional operation).
boolean	retainAll(Collection<? > c) Retains only the elements in this collection that are contained in the specified collection (optional operation).
int	size() Returns the number of elements in this collection.
Object[]	toArray() Returns an array containing all of the elements in this collection.
<T> T[]	toArray(T[] a) Returns an array containing all of the elements in this collection; the runtime type of the returned array is that of the specified array.

上图中，Set与List、Map都是Collection的子类。

它们的差别在于,Set实现的类仅仅能存放无序、无反复的数据对象。而List仅仅存放的是有序，可反复的数据对象。Map接口定义了存储着"键（key）-值（value）映射对的方法。

以下代码示范List继承collection接口并实现它部分的相关方法：

<pre name="code" class="java">     package CrazyStone;

import java.util.ArrayList;
import java.util.List;
public class DemoList {
   public static void main(String[] args) {
		int value;
	    List list=new  ArrayList();                            //定义List类对象list,并实现父类引用。
	    list.add("CSDN");            //加入数据对象方法；
	    list.add("GB记忆");
        System.out.println(   list.isEmpty());       //推断list容器是否为空
        value=list.size();              //返回容器的大小；
        for(int i=0;i<value;i++)       //遍历容器。
        {  String str =(String) list.get(i);
           System.out.println(str);

        }
        System.out.println("---------------------");
      //跟顺序有关的操作
        list.remove(0);               //在容器中移出CSDN。但并未删除。
        list.set(0, "CSDNGO");  //向容器中插入对象；
       list.add("加油。");
       value=list.size();
       for(int i=0;i<value;i++)       //遍历容器；
       {  String str =(String) list.get(i);
          System.out.println(str);

       }
	}

}