Handwritten code Precautions - HashMap

1. Definitions

HashMap<String,String> hashMap = new HashMap<>();

<String, String> just write it again

 

2. Obtain key and value

        //get a key/value set
        hashMap.keySet();
        hashMap.values();

        //judge whether contains key/value
        hashMap.containsKey("key");
        hashMap.containsValue("value");    

 

3. traversal

        //loop
        for(Map.Entry<String, String> item: hashMap.entrySet()) {
            item.getKey();
            item.getValue();
        }