The four traversal methods of the map set can be seen at a glance

Traverse Map And traversal List There's a big difference , Beginners have never touched map You may not understand the code , I'd like to make a brief statement here .

Map The element stored in is in the form of “ Key value pair ” The way , That is to say key-value Yes .
Map.Entry yes Map One of the interfaces in , Its purpose is to represent a mapping item （ There are Key and Value）, As shown in the figure below ：

So we can traverse through Map Of entrySet() Method , It returns an implementation Map.Entry Object collection of interface , Every entry Object to store the pair K-V Yes . We can call... Through this object getKey() and getValue() Get what you need easily key and value

The second and third traversal methods in the following code are used entrySet() Method

//Map Four ways to traverse a set 
public class MapDemo {
    
    public static void main(String[] args) {
    
        Map<String, Integer> map = new HashMap<>();
        map.put("tom",11);
        map.put("cindy",22);
        map.put("marry",42);
        //1、 The first traversal method , obtain key--> to value
        for(String key : map.keySet()){
      //keySet() Returns the... Of the key contained in this map Set View 
            System.out.print(key+"="+ map.get(key)+" ");
        }

        //2、 The second traversal method , adopt Map.entrySet Use iterator Traverse key and value
        Set<Map.Entry<String, Integer>> entries = map.entrySet(); //entrySet() Returns the... Contained in this map entry Of Set View 
        Iterator<Map.Entry<String, Integer>> iterator = entries.iterator();
        while (iterator.hasNext()){
    
            Map.Entry<String, Integer> next = iterator.next();
            System.out.print(next.getKey()+"="+next.getValue()+" ");
        }

        //3、 The third way of traversal , adopt Map.entrySet Traverse key and value
        for (Map.Entry<String,Integer> entry : map.entrySet()){
    
            System.out.print(entry.getKey()+"="+entry.getValue()+" ");
        }

        //4、 The fourth way of traversal , adopt Map.values() Traverse all value, But you can't traverse key
        for (Integer integer: map.values()){
    
            System.out.print("value="+integer+" ");
        }
    }
}