Interpretation of Java documentation: Detailed explanation of the usage of the size() method of the HashMap class

Interpretation of Java documentation: Detailed explanation of the usage of the size() method of the HashMap class, specific code examples are required

In Java, HashMap is a commonly used data structure. Provides a way to store key-value pairs. The size() method of the HashMap class is used to return the number of key-value pairs in the HashMap.

The specific code examples are as follows:

import java.util.HashMap;

public class HashMapSizeExample {
    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("orange", 3);

        // 使用size()方法获取HashMap中键值对的数量
        int size = map.size();

        // 打印HashMap中键值对的数量
        System.out.println("HashMap中键值对的数量为：" + size);
    }
}

In the above code example, we first created a HashMap object and added three key-value pairs to the HashMap using the put() method. Then use the size() method to get the number of key-value pairs in the HashMap, and store the result in the variable size. Finally, use System.out.println() to print out the number of key-value pairs in the HashMap.

Run the above code, the output result is:

HashMap中键值对的数量为：3

The above code example shows how to use the size() method of HashMap to obtain the number of key-value pairs in the HashMap. The size() method is an instance method provided by the HashMap class. You only need to call this method to return the number of key-value pairs in the HashMap.

It should be noted that the size() method returns the number of key-value pairs in the HashMap, not the capacity. Capacity refers to the length of the underlying array of HashMap. In HashMap, the capacity changes dynamically. When the number of key-value pairs exceeds the current capacity of HashMap, the capacity will be expanded automatically.

In actual development, we often use HashMap to store data, and use the size() method to obtain the amount of data in the HashMap to perform related business logic processing.

To summarize, the size() method of the HashMap class is used to return the number of key-value pairs in the HashMap. This method can be used to easily obtain the amount of data in the HashMap and help us perform related business logic processing. At the same time, it should be noted that the size() method returns the number of key-value pairs, not the capacity.

Hope the above is helpful to the usage of the size() method of the HashMap class, allowing you to better understand and use the HashMap class.

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