Use the containsAll() method of the HashSet class to determine whether one set contains all elements in another set

Use the containsAll() method of the HashSet class to determine whether a collection contains all elements in another collection

HashSet is an unordered, non-duplicate collection class provided by the Java collection framework. It is implemented based on a hash table and can quickly insert, delete, and search elements. In many scenarios, we need to determine whether a set contains all elements in another set. Java provides the containsAll() method to meet this requirement.

The code example is as follows:

import java.util.HashSet;

public class HashSetContainsAllExample {
    public static void main(String[] args) {
        // 创建两个HashSet集合
        HashSet<Integer> set1 = new HashSet<Integer>();
        HashSet<Integer> set2 = new HashSet<Integer>();

        // 向set1中添加元素
        set1.add(1);
        set1.add(2);
        set1.add(3);
        set1.add(4);

        // 向set2中添加元素
        set2.add(2);
        set2.add(4);

        // 使用containsAll()方法判断set1是否包含set2中的所有元素
        boolean result = set1.containsAll(set2);

        if (result) {
            System.out.println("set1包含set2中的所有元素");
        } else {
            System.out.println("set1不包含set2中的所有元素");
        }
    }
}

In the above code, we created two HashSet sets (set1 and set2) and added elements 1, 2, 3 and 4 to set1 , elements 2 and 4 are added to set2. Then, we use the containsAll() method to determine whether set1 contains all elements in set2. Finally, the corresponding information is printed based on the returned results.

Run the above code, you will get the following output:

set1不包含set2中的所有元素

Explanation that set1 does not contain all elements in set2. This is because element 2 is missing from set1, so the containsAll() method returns false.

Using the containsAll() method can very conveniently determine whether a collection contains all elements in another collection. This method is not only applicable to HashSet, but other collection classes that implement the Set interface (such as TreeSet).

It should be noted that the judgment of the containsAll() method is based on the equals() method of the element, not based on the memory address. This means that when we determine whether two sets are equal, we only need to compare whether the elements in them are equal, and do not need to compare whether their reference addresses are equal.

To summarize, using the containsAll() method of the HashSet class can easily and efficiently determine whether a set contains all elements in another set. This method is very useful in actual development and can help us quickly solve related problems.

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