Use java's HashMap.size() function to get the size of a HashMap

Use java's HashMap.size() function to get the size of HashMap

In Java, HashMap is a commonly used collection class that is used to store key-value pairs. HashMap provides a series of convenient methods to operate on the elements in the collection, one of which is the size() function, which is used to obtain the number of elements in the HashMap. In this article, we will introduce how to use the size() function of HashMap to obtain the size of a HashMap, and provide code examples.

First of all, we need to understand the basic concept of HashMap. HashMap is an implementation based on a hash table, which uses key-value pairs to store data. Each key-value pair is an Entry object, which contains the key and value. When we add an element to a HashMap, we first find the corresponding position based on the hash value of the key, and then insert the key-value pair into the hash table. When we need to use a key to obtain a value, HashMap will quickly find the corresponding location based on the hash value of the key, thus improving the efficiency of the search.

The size() function of HashMap is used to obtain the number of elements in HashMap. It returns a value of type int, indicating the number of key-value pairs in the HashMap. We can use this function to determine whether the HashMap is empty or to get the size of the HashMap.

The following is a code example that uses the size() function of HashMap to obtain the size of a HashMap:

import java.util.HashMap;

public class HashMapSizeExample {

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

        // 添加元素到HashMap中
        hashMap.put("key1", "value1");
        hashMap.put("key2", "value2");
        hashMap.put("key3", "value3");

        // 使用size()函数获取HashMap的大小
        int size = hashMap.size();

        // 打印HashMap的大小
        System.out.println("HashMap的大小为：" + size);
        
        // 判断HashMap是否为空
        boolean isEmpty = hashMap.isEmpty();

        // 打印HashMap是否为空
        System.out.println("HashMap是否为空：" + isEmpty);
    }
}

In the above code example, a HashMap object is first created and the put() function is used Three key-value pairs have been added. Then use the size() function to get the size of the HashMap and save the result in the variable size. Finally, use the println() function to print the size of the HashMap. Run the above code, and the output result is as follows:

HashMap的大小为：3
HashMap是否为空：false

As can be seen from the output result, the size of HashMap is 3, and the HashMap is not empty.

To sum up, the size of HashMap can be easily obtained by using the size() function of HashMap in Java. We only need to create a HashMap object, add key-value pairs, and then call the size() function to get the size of the HashMap. By using the size() function, we can operate HashMap more conveniently and perform corresponding business logic processing. Hope this article helps you!

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