遍历HashMap的常用两种方式

最近做一个小项目用到了HashMap，一头雾水，说明自己的基础知识真的很不扎实。从网上查资料整理了两种常用的遍历HashMap的方法：

 

import java.util.ArrayList;import java.util.HashMap;import java.util.Iterator;import java.util.Map.Entry;

 

 

public class HashMapTest { public static void main(String args[]) {  HashMap<String, Object> hash = new HashMap<String, Object>();  Person p1 = new Person("张三", 20);  Person p2 = new Person("李四", 21);  hash.put("p1", p1);  hash.put("p2", p2);  ArrayList<String> a = new ArrayList<String>();  a.add("jia");  a.add("hello");  hash.put("a", a);  

//方法一：遍历key  System.out.println("---------------遍历Key--------------");  Iterator it1 = hash.keySet().iterator();   

  while (it1.hasNext()) {   Object key = it1.next();   Object val = hash.get(key);   System.out.println("key: " + key + "/tval: " + val);  }

 

 

//方法二：遍历key和value封装的实体  System.out.println("----------遍历Key和Value封装的实体--------");  Iterator it2 = hash.entrySet().iterator();

  while (it2.hasNext()) {   Entry entry = (Entry) it2.next();   Object key = entry.getKey();   Object val = entry.getValue();   if (key.equals("p1"))    entry.setValue("bye");   System.out.println("key: " + key + "/tval: " + val);  } }}

 

 //Person类

class Person { String name; int age;

 public Person(String name, int age) {  this.name = name;  this.age = age; }

 public String toString() {  return name + "  " + age; }}

 

运行结果：

---------------遍历Key--------------key: p1 val: 张三  20key: a val: [jia, hello]key: p2 val: 李四  21----------遍历Key和Value封装的实体--------key: p1 val: 张三  20key: a val: [jia, hello]key: p2 val: 李四  21