How to insert key-value pairs into HashMap using put() method of HashMap class

How to use the put() method of the HashMap class to insert key-value pairs into a HashMap

HashMap is a very important class in the Java collection framework. It provides a way to store key-value pairs. . In actual development, we often need to insert key-value pairs into HashMap, which can be easily achieved by using the put() method of the HashMap class.

The signature of the put() method of HashMap is as follows:

V put(K key, V value)

where K represents the type of key and V represents the type of value . The put() method accepts two parameters, one is the key and the other is the value. It inserts the specified key-value pair into the HashMap and replaces the old value (if it exists) with the new value. If multiple values ​​are inserted using the same key, each value is inserted into a HashMap and the last inserted value is always returned.

The following is a sample code that uses the put() method of the HashMap class to insert key-value pairs into a HashMap:

import java.util.HashMap;

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

        // 使用put()方法将键值对插入到HashMap中
        hashMap.put("apple", 1);
        hashMap.put("banana", 2);
        hashMap.put("orange", 3);

        // 打印HashMap中的键值对
        System.out.println("HashMap: " + hashMap);
    }
}

The above code first imports java.util.HashMapClass, and then create a HashMap object hashMap in the main() method. Then use the put() method to insert the three key-value pairs into the HashMap in sequence. The keys are "apple", "banana" and " orange", the corresponding values ​​are 1, 2 and 3 respectively. Finally, print the key-value pairs in the HashMap by calling the System.out.println() method.

Run the above code, the following results will be output:

HashMap: {orange=3, banana=2, apple=1}

You can see that the key-value pairs in the HashMap are correctly inserted and sorted according to the order of insertion.

It should be noted that the keys in HashMap must be unique. If the same key is inserted, the new value will overwrite the old value. The value can be of any type, either a primitive type or a reference type.

Another thing to note is that when inserting a key-value pair into a HashMap, if the key already exists, the put() method will return the old value corresponding to the key. If the key does not exist, the put() method will return null.

To summarize, you can easily insert key-value pairs into a HashMap using the put() method of the HashMap class. By passing key and value as parameters, key-value pairs can be saved into a HashMap and the corresponding value can be retrieved by key. At the same time, if the same key is inserted, the new value will replace the old value. I hope the above example will help you understand how to use the put() method of HashMap.

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