Map接口的遍历实现

Map接口的四种遍历方式

1. 使用Set集合迭代器方法
   1）先使用keySet方法获取关键字集合的Set集合
   2）再根据Set集合的iterator方法得到相应的迭代器
   3）根据Set的迭代器进行遍历
   4）关键代码如下

方式一：迭代器while循环

System.out.println("==========遍历方式一==========");
		Set keySet = map.keySet();
		Iterator iterator = keySet.iterator();
		while(iterator.hasNext()){
			Object key = iterator.next();
			System.out.println(key+"---"+map.get(key));
		}

方式二：增强for循环

System.out.println("==========遍历方式二==========");
		for (Object key1 : keySet) {
			System.out.println(key1+"---"+map.get(key1));
		}

2. 使用entrySet迭代器方法
   1）先使用Map接口的entrySet方法得到一个Set集合
   2）根据得到的Set集合得到新的iterator迭代器
   3）根据迭代器进行遍历

方式三

System.out.println("==========遍历方式三==========");
		Set entrySet = map.entrySet();
		Iterator iterator2 = entrySet.iterator();
		while(iterator2.hasNext()){
			Map.Entry node = (Map.Entry)iterator2.next();
			System.out.println(node.getKey()+"---"+node.getValue());
		}

方式四

System.out.println("==========遍历方式四==========");
		for (Object object : entrySet) {
			Map.Entry node2 = (Map.Entry)object;
			System.out.println(node2.getKey()+"---"+node2.getValue());
		}

3. 最后附上完整的代码

代码

package Test;

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;

public class MapForeach {
	@SuppressWarnings({ "unchecked", "rawtypes" })
	public static void main(String[] args) {
		HashMap map = new HashMap();
		Student student1 = new Student("001","汤小强");
		Student student2 = new Student("002","汤大强");
		Student student3 = new Student("003","汤很强");
		Student student4 = new Student("004","汤最强");
		map.put(student1.getID(), student1);
		map.put(student2.getID(), student2);
		map.put(student3.getID(), student3);
		map.put(student4.getID(), student4);
		
		System.out.println("==========遍历方式一==========");
		Set keySet = map.keySet();
		Iterator iterator = keySet.iterator();
		while(iterator.hasNext()){
			Object key = iterator.next();
			System.out.println(key+"---"+map.get(key));
		}
		
		
		System.out.println("==========遍历方式二==========");
		for (Object key1 : keySet) {
			System.out.println(key1+"---"+map.get(key1));
		}
		
		System.out.println("==========遍历方式三==========");
		Set entrySet = map.entrySet();
		Iterator iterator2 = entrySet.iterator();
		while(iterator2.hasNext()){
			Map.Entry node = (Map.Entry)iterator2.next();
			System.out.println(node.getKey()+"---"+node.getValue());
		}
		
		System.out.println("==========遍历方式四==========");
		for (Object object : entrySet) {
			Map.Entry node2 = (Map.Entry)object;
			System.out.println(node2.getKey()+"---"+node2.getValue());
		}
	}
}


class Student{
	private String name;
	private String ID;
	public Student(String iD, String name ) {
		super();
		this.name = name;
		ID = iD;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public String getID() {
		return ID;
	}
	public void setID(String iD) {
		ID = iD;
	}
	@Override
	public String toString() {
		// TODO Auto-generated method stub
		return "ID ="+ID+" name="+name;
	}
}