Java study notes-some usage of Map

Traverse key and value according to Map.Entry()

Set<Map.Entry<String, String>> entryseSet=map.entrySet();
 
for (Map.Entry<String, String> entry:entryseSet) {
 
    System.out.println(entry.getKey()+","+entry.getValue());
 
}

 

Traverse according to KeySet to get key and value

Set<String> set = map.keySet();
 
for (String s:set) {
 
    System.out.println(s+","+map.get(s));
 
}

 

Traverse according to Values, only value can be obtained

Set<String> set = map.values();

        for (String s:set) {

            System.out.println(s);

        }

 

Map.getOrDefault()

Usage: Map.getOrDefault(key, default value);

One-to-one correspondence of key and value will be stored in the Map.
If there is a key in the Map, the value corresponding to the key is returned.
If the key does not exist in the Map, the default value is returned.

public class Demo {
    public static void main(String[] args) {
        Map<String, Integer> map = new HashMap<>();
        map.put("张三", 23);
        map.put("赵四", 24);
        map.put("王五", 25);
        String age= map.getOrDefault("赵四", 30);
        System.out.println(age);// 24，map中存在"赵四",使用其对应值24
        String age = map.getOrDefault("刘能", 30);
        System.out.println(age);// 30，map中不存在"刘能",使用默认值30
    }
}