Map collection of three kinds of traversal

Map collection of three kinds of traversal

1. iterates over

package lession02;

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

public class Demo2 {
    public static void main(String[] args) {
        Map<String,String> map = new HashMap<>();
        
        map.put("杨过", "男");
        map.put("小龙女", "女");
        map.put("蛮子", "男");
        map.put("艾希","女");
        
        System.out.println(map);
        // 遍历map集合
        // 1.迭代器遍历
        Set<String> keySets = map.keySet(); 
        Iterator<String> ki = keySets.iterator();
        
        while(ki.hasNext()){
            String k = ki.next();
            String v = map.get(k);
            
            System.out.println(k+"-->"+v);
        }
    
    }
}

operation result

2. Enhance for traversing (internal principle: iterator traversal)

package lession02;

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

public class Demo3 {
    public static void main(String[] args) {
        Map<String,String> map = new HashMap<>();
        
        map.put("杨过", "男");
        map.put("小龙女", "女");
        map.put("蛮子", "男");
        map.put("艾希","女");
        
        System.out.println(map);
        Set<String> keySets = map.keySet(); 
        // 2.增强for循环遍历
        for(String key:keySets){
            String value = map.get(key);
            System.out.println(key+"---->"+value);
        }
        
    }
}

operation result

3.entrySet traversal

package lession02;

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

public class Demo4 {
    public static void main(String[] args) {
        Map<String,String> map = new HashMap<>();
        
        map.put("杨过", "男");
        map.put("小龙女", "女");
        map.put("蛮子", "男");
        map.put("艾希","女");  
        
        System.out.println(map);
        // 3.entrySet遍历
        Set<Entry<String, String>> entry =  map.entrySet();
        for(Entry<String, String> en:entry){
            System.out.println(en.getKey()+"--->"+en.getValue());
        }
    }
}

operation result

Entry方式遍历过程模拟