Java 数据结构 - 集合的差集

假设我们通过添加两个（或多个）集合的内容来创建了一个集合对象，当您需要完全从该集合中删除特定集合的内容时，可以使用 removeAll() 方法来实现。

此方法属于 Set 接口，并且继承自 Collection 接口。它接受一个集合对象，并立即从当前 Set（对象）中完全删除其内容。

示例

import java.util.HashSet;
import java.util.Set;

public class SubtractingTwoSets {
   public static void main(String args[]) {      
      Set set1 = new HashSet();      
      set1.add(100);
      set1.add(501);
      set1.add(302);
      set1.add(420);
      System.out.println("Contents of set1 are: ");
      System.out.println(set1); 

      Set set2 = new HashSet();      
      set2.add(200);
      set2.add(630);
      set2.add(987);
      set2.add(665);
      System.out.println("Contents of set2 are: ");
      System.out.println(set2); 
      
      set1.addAll(set2);
      System.out.println("Contents of set1 after addition: ");
      System.out.println(set1);
      
      set1.removeAll(set2);
      System.out.println("Contents of set1 after removal");
      System.out.println(set1);
   }
}

输出

Contents of set1 are: 
[100, 420, 501, 302]
Contents of set2 are: 
[630, 200, 665, 987]
Contents of set1 after addition: 
[100, 420, 501, 630, 200, 665, 987, 302]
Contents of set1 after removal
[100, 420, 501, 302]