Commons Collections 简明教程

Apache Commons Collections - Union

Apache Commons Collections 库的 CollectionUtils 类提供各种实用方法，用于涵盖广泛使用场景的常见操作。它有助于避免编写样板代码。在 jdk 8 之前，该库非常有用，因为 Java 8 的 Stream API 中现在提供了类似的功能。

CollectionUtils class of Apache Commons Collections library provides various utility methods for common operations covering wide range of use cases. It helps avoid writing boilerplate code. This library is very useful prior to jdk 8 as similar functionalities are now provided in Java 8’s Stream API.

Checking union

CollectionUtils 的 union() 方法可用于获取两个集合的并集。

union() method of CollectionUtils can be used to get the union of two collections.

Declaration

以下是 org.apache.commons.collections4.CollectionUtils.union() 方法的声明 -

Following is the declaration for org.apache.commons.collections4.CollectionUtils.union() method −

public static <O> Collection<O> union(Iterable<? extends O> a, Iterable<? extends O> b)

Parameters

  1. a − The first collection, must not be null.

  2. b − The second collection, must not be null.

Return Value

两个集合的并集。

The union of the two collections.

Example

以下示例显示了 org.apache.commons.collections4.CollectionUtils.union() 方法的用法。我们将获得两个列表的并集。

The following example shows the usage of org.apache.commons.collections4.CollectionUtils.union() method. We’ll get the union of two lists.

import java.util.Arrays;
import java.util.List;
import org.apache.commons.collections4.CollectionUtils;

public class CollectionUtilsTester {
   public static void main(String[] args) {
      //checking inclusion
      List<String> list1 = Arrays.asList("A","A","A","C","B","B");
      List<String> list2 = Arrays.asList("A","A","B","B");

      System.out.println("List 1: " + list1);
      System.out.println("List 2: " + list2);
      System.out.println("Union of List 1 and List 2: "+ CollectionUtils.union(list1, list2));
   }
}

Output

生成以下输出：

This produces the following output −

List 1: [A, A, A, C, B, B]
List 2: [A, A, B, B]
Union of List 1 and List 2: [A, A, A, B, B, C]