How to add key-value pairs to a map using HashMap.put() method in Java?

Use the HashMap.put() method in Java to add key-value pairs to the map

HashMap is a class in the Java collection framework, used to store key-value pairs . It implements the Map interface and stores data according to the hash value of the key, so data can be quickly found and retrieved. This article will introduce how to use the put() method of HashMap to add key-value pairs to the map.

The put() method of HashMap is a method used to add key-value pairs to the map. It is defined as follows:

V put(K key, V value)

where K represents the type of key and V represents the value. type. The parameter key represents the key to be added, and the parameter value represents the value to be added. The put() method will add the specified key-value pair to the HashMap. If the key already exists, it will overwrite the old value with the new value and return the replaced value; if the key does not exist, the key value will be directly The pair is added to the HashMap and returns null.

The following is a simple sample code showing how to use the put() method of HashMap to add key-value pairs to the map:

import java.util.HashMap;

public class HashMapExample {
    public static void main(String[] args) {
        // 创建一个HashMap对象
        HashMap<String, Integer> map = new HashMap<>();

        // 添加键值对到HashMap中
        map.put("apple", 1);
        map.put("banana", 2);
        map.put("cherry", 3);

        // 打印HashMap中的键值对
        for (String key : map.keySet()) {
            Integer value = map.get(key);
            System.out.println(key + " : " + value);
        }
    }
}

The above code first creates a HashMap object, and then uses The put() method adds three key-value pairs to the map. Finally, use a for loop to traverse the HashMap key collection, obtain the value corresponding to each key, and print it out.

Run the above code, the output result is as follows:

cherry : 3
apple : 1
banana : 2

You can see that the key-value pairs are successfully added to the HashMap through the put() method, and sorted according to the order of insertion.

Summary:

This article introduces the use of the put() method of HashMap in Java, which is used to add key-value pairs to the map. The sample code shows how to use the put() method to add key-value pairs to a HashMap, and how to traverse the HashMap to obtain the key-value pairs. I hope this article will help you understand the use of HashMap.

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