Interpretation of Java documentation: Detailed explanation of usage of containsAll() method of HashSet class

Interpretation of Java documentation: Detailed explanation of usage of containsAll() method of HashSet class, specific code examples are required

1. Introduction

HashSet class in Java It is an unordered, non-duplicate collection, which is implemented based on a hash table. When using the HashSet class, we may often use the containsAll() method to determine whether the set contains all elements of another set. This article will explain in detail the usage of the containsAll() method of the HashSet class and provide specific code examples for demonstration.

2. Definition and description of containsAll() method

In Java’s HashSet class, the containsAll() method is defined as follows:

public boolean containsAll(Collection > c)

This method is used to determine whether the current HashSet contains all elements of another Collection object, and returns a Boolean value indicating whether all elements are included.

3. Example of using the ContainsAll() method

Below we demonstrate the use of the containsAll() method through a specific code example.

import java.util.HashSet;
import java.util.Arrays;

public class HashSetDemo {
    public static void main(String[] args) {
        HashSet<String> hashSet1 = new HashSet<>(Arrays.asList("A", "B", "C", "D"));
        HashSet<String> hashSet2 = new HashSet<>(Arrays.asList("A", "C"));

        System.out.println("HashSet1：" + hashSet1);
        System.out.println("HashSet2：" + hashSet2);

        // 判断hashSet1是否包含hashSet2中的所有元素
        boolean result = hashSet1.containsAll(hashSet2);

        System.out.println("HashSet1是否包含HashSet2的所有元素？" + result);
    }
}

In this example, we created two HashSet objects hashSet1 and hashSet2. We use the Arrays.asList() method to add elements to the HashSet, which is convenient and fast. Then, we use the containsAll() method to determine whether hashSet1 contains all elements of hashSet2. Finally, print the results.

4. Running results

Running the above code, we can get the following output:

HashSet1：[A, B, C, D]
HashSet2：[A, C]
HashSet1是否包含HashSet2的所有元素？true

As can be seen from the results, HashSet1 contains all elements of HashSet2, so the result is true.

5. Summary

In this article, we introduced in detail the usage of the containsAll() method of the HashSet class in Java. The containsAll() method can be used to determine whether a HashSet object contains all elements of another collection. We demonstrate the steps of using the containsAll() method through a specific code example, as well as the output results.

By using the containsAll() method, we can easily judge the inclusion relationship of the elements in the HashSet. This is very useful for processing set operations, set intersection, etc. I hope this article can help readers better understand and use the containsAll() method of the HashSet class.

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