HashMap

/*
 *此处以HashMap为例，罗列了一些映射的基本操作。
 */

package classfile;

import java.util.*;

public class HashMapDemo
{
	public static void main(String[] args)
	{
		method_create();
		method_delete();
		method_update();
		method_read();
	}

	public static void method_create()
	{
		HashMap<String,Integer> hmOne = new HashMap<String,Integer>();
		HashMap<String,Integer> hmTwo = new HashMap<String,Integer>();

		//添加单个元素
		hmOne.put("java01",11);
		hmOne.put("java02",12);
		hmOne.put("java03",13);
		System.out.println(hmOne);

		hmTwo.put("java001",111);
		hmTwo.put("java002",112);
		System.out.println(hmTwo);

		//添加一个Map集合
		hmOne.putAll(hmTwo);
		System.out.println(hmOne);
	}

	public static void method_delete()
	{
		HashMap<String,Integer> hmOne = new HashMap<String,Integer>();

		hmOne.put("java01",11);
		hmOne.put("java02",12);
		hmOne.put("java03",13);
		System.out.println(hmOne);

		//移除指定键的映射项
		hmOne.remove("java01");
		System.out.println("移除指定键的映射项后的集合:"+hmOne);

		//清空Map集合
		hmOne.clear();
		System.out.println("被清空后的集合:"+hmOne);
	}

	public static void method_update()
	{
		HashMap<String,Integer> hmOne = new HashMap<String,Integer>();

		hmOne.put("java01",11);
		hmOne.put("java02",12);
		hmOne.put("java03",13);
		System.out.println("被修改前的集合:"+hmOne);

		//修改值是通过添加来实现的
		hmOne.put("java01",22);
		System.out.println("被修改后的集合:"+hmOne);

		//修改键要先删除再添加
		hmOne.remove("java01");
		hmOne.put("java04",14);
		System.out.println("被修改后的集合:"+hmOne);
	}

	public static void method_read()
	{
		HashMap<String,Integer> hmOne = new HashMap<String,Integer>();

		hmOne.put("java01",11);
		hmOne.put("java02",12);
		hmOne.put("java03",13);
		System.out.println(hmOne);

		//判断Map集合中是否包含指定的键
		System.out.println("Map集合中是否包含指定的键:"+hmOne.containsKey("java01"));

		//判断Map集合中是否包含指定的值
		System.out.println("Map集合中是否包含指定的值:"+hmOne.containsValue(11));

		//获取Map集合映射项的Set视图
		Set<Map.Entry<String,Integer>> setOne = hmOne.entrySet();
		for(Iterator<Map.Entry<String,Integer>> iterator = setOne.iterator();iterator.hasNext();)
		{
			Map.Entry<String,Integer> me = iterator.next();

			System.out.println("Map集合中的键和值:"+me.getKey()+"..."+me.getValue());
		}

		//根据指定的键获取相应的值
		System.out.println("根据指定的键获取相应的值:"+hmOne.get("java01"));

		//判断Map集合是否为空
		System.out.println("判断集合是否为空:"+hmOne.isEmpty());

		//获取Map集合键的Set视图
		Set<String> setTwo = hmOne.keySet();
		for(Iterator<String> iterator = setTwo.iterator();iterator.hasNext();)
		{
			String str = iterator.next();

			System.out.println("Map集合中的键和值:"+str+"..."+hmOne.get(str));
		}

		//获取Map集合的大小
		System.out.println("Map集合的大小:"+hmOne.size());

		//获取Map集合值的Collection视图
		Collection<Integer> collection = hmOne.values();
		for(Iterator<Integer> iterator = collection.iterator();iterator.hasNext();)
		{
			System.out.println("Map集合的值为:"+iterator.next());
		}
	}
}