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）：

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);
       
       }
	}
   
}