JAVA学习第三十九课（常用对象API）- 集合框架（七）— Map集合及其子类对象

一、Map集合常见子类

HashTable：内部结构是哈希表，同步，此实现提供所有可选的映射操作，不允许使用 null 值和 null 键

（HashTable下有子类Properties，使用频率非常高，用来存储键值对型的配置文件信息和IO技术相结合）

HashMap：内部结构是哈希表，不同步，此实现提供所有可选的映射操作，并允许使用 null 值和 null 键。

TreeMap：内部结构是二叉树，不同步，可以对Map集合中的键进行排序。

二、HashMap演示

import java.util.Collection;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
class Man
{
	private String name;
	private int age;
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public int getAge() {
		return age;
	}
	public void setAge(int age) {
		this.age = age;
	}
	public Man(String name, int age) {
		super();
		this.name = name;
		this.age = age;
	}
	public Man() {
		super();
		// TODO Auto-generated constructor stub
	}
	@Override
	public int hashCode() {
		final int prime = 31;
		int result = 1;
		result = prime * result + age;
		result = prime * result + ((name == null) ? 0 : name.hashCode());
		return result;
	}
	@Override
	public boolean equals(Object obj) {
		if (this == obj)
			return true;
		if (obj == null)
			return false;
		if (getClass() != obj.getClass())
			return false;
		Man other = (Man) obj;
		if (age != other.age)
			return false;
		if (name == null) {
			if (other.name != null)
				return false;
		} else if (!name.equals(other.name))
			return false;
		return true;
	}
}
public class Main
{
	public static void main(String[] args) {
		HashMapDemo();
	}
	public static void HashMapDemo(){
		//人和籍贯 通过键值对存储在HashMap中
		HashMap<Man, String> hm = new HashMap<Man,String>();
		hm.put(new Man("周",1),"上海");
		hm.put(new Man("周",1),"东北");//要保证哈希表，所以Man中的HashCode和equals方法要复写
		hm.put(new Man("王",4),"北京");
		hm.put(new Man("孙",2),"广州");
		hm.put(new Man("赵",6),"山东");

		Iterator<Man> it =  hm.keySet().iterator();
		while(it.hasNext()){
			Man man = it.next();
			String bir = hm.get(man);
			System.out.println("man - bir :"+man.getName()+","+man.getAge()+" - "+bir);
		}
	}
}

三、TreeMap演示

import java.util.Collection;
import java.util.Comparator;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
import java.util.TreeMap;
class Man extends Object
{
	private String name;
	private int age;
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public int getAge() {
		return age;
	}
	public void setAge(int age) {
		this.age = age;
	}
	public Man(String name, int age) {
		super();
		this.name = name;
		this.age = age;
	}
	public Man() {
		super();
		// TODO Auto-generated constructor stub
	}
	@Override
	public int hashCode() {
		final int prime = 31;
		int result = 1;
		result = prime * result + age;
		result = prime * result + ((name == null) ? 0 : name.hashCode());
		return result;
	}
	@Override
	public boolean equals(Object obj) {
		if (this == obj)
			return true;
		if (obj == null)
			return false;
		if (getClass() != obj.getClass())
			return false;
		Man other = (Man) obj;
		if (age != other.age)
			return false;
		if (name == null) {
			if (other.name != null)
				return false;
		} else if (!name.equals(other.name))
			return false;
		return true;
	}
}
class Compararule implements Comparator<Object>
{
	 public int compare(Object arg0, Object arg1) {
		 if(!(arg0 instanceof Man))
	            throw new ClassCastException();  

	            Man man = (Man)arg0;
	            Man man2 = (Man)arg1;
	        int te = man.getAge() - man2.getAge();
	        return te==0?man.getName().compareTo(man2.getName()):te;
	    }
}
public class Main
{
	public static void main(String[] args) {
		TreeMapDemo();
	}
	public static void TreeMapDemo(){
		TreeMap<Man, String> tm = new TreeMap<Man,String>(new Compararule());
		tm.put(new Man("zhou",1),"上海");
		tm.put(new Man("zhou",1),"东北");//要保证哈希表，所以Man中的HashCode和equals方法要复写
		tm.put(new Man("wang",4),"北京");
		tm.put(new Man("sun",2),"广州");
		tm.put(new Man("zhao",6),"山东");

		Iterator<Map.Entry<Man,String>> it =  tm.entrySet().iterator();
		while(it.hasNext()){
			Map.Entry<Man, String> mEntry = it.next();
			Man man = mEntry.getKey();
			String bir = mEntry.getValue();
			System.out.println("man - bir :"+man.getName()+","+man.getAge()+" - "+bir);
		}
	}
}

集合框架的三大集合：List、Set、Map，到此就结束了

看到tree，二叉树，排序，两大接口Comparator，Comparable

而Map自身没有迭代器，但是可以通过keySet，entry返回Set映射，再通过Set的迭代器，访问键值对

明天就是泛型的学习。要重点掌握，加油！！！