Java CopyOnWriteArrayList .retainAll()方法及示例

Java中的 Java.util.concurrent.CopyOnArrayList .retainAll() 方法用于仅保留列表中包含在特定集合中的元素。

语法

 public boolean retainAll(Collection col) 

参数： 该方法接受一个强制性参数 col ，其类型为集合。这是要保留在这个向量中的元素集合。

返回类型： 如果调用的结果是改变了列表，该方法返回一个 布尔值 true，否则返回false。

异常： 如果指定的集合是空的，该方法会抛出一个NullPointerException。

下面的程序说明了Java中CopyOnArrayList的retainAll()方法。

程序1： 该程序涉及整数类型的CopyOnArraylist retainAll()方法。

// Java Program to illustrate CopyOnArrayList
// retainAll() method
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.*;
  
public class GFG {
    public static void main(String[] args)
    {
        // create object of CopyOnWriteArrayList
        CopyOnWriteArrayList<Integer> ArrLis1
            = new CopyOnWriteArrayList<Integer>();
  
        // Add elements
        ArrLis1.add(34);
        ArrLis1.add(66);
        ArrLis1.add(72);
        ArrLis1.add(10);
  
        // print CopyOnWriteArrayList
        System.out.println("CopyOnWriteArrayList1: "
                           + ArrLis1);
  
        // create object of CopyOnWriteArrayList
        CopyOnWriteArrayList<Integer> ArrLis2
            = new CopyOnWriteArrayList<Integer>();
  
        // Add elements
        ArrLis2.add(10);
        ArrLis2.add(66);
        ArrLis2.add(97);
  
        // print CopyOnWriteArrayList
        System.out.println("CopyOnWriteArrayList2: "
                           + ArrLis2);
  
        // Applying the function
        ArrLis2.retainAll(ArrLis1);
  
        // print CopyOnWriteArrayLists
  
        System.out.println("After applying retainAll()"
                           + " method on ArrLis2");
        System.out.println("CopyOnWriteArrayList1: "
                           + ArrLis1);
        System.out.println("CopyOnWriteArrayList2: "
                           + ArrLis2);
    }
}

输出。

CopyOnWriteArrayList1: [34, 66, 72, 10]
CopyOnWriteArrayList2: [10, 66, 97]
After applying retainAll() method on ArrLis2
CopyOnWriteArrayList1: [34, 66, 72, 10]
CopyOnWriteArrayList2: [10, 66]

程序2： 该程序涉及到字符串类型的CopyOnArraylist retainAll（）方法。

// Java Program to illustrate CopyOnArrayList
// retainAll() method
  
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.*;
  
public class GFG {
    public static void main(String[] args)
    {
        CopyOnWriteArrayList<String> ArrLis1
            = new CopyOnWriteArrayList<String>();
  
        // Add elements
        ArrLis1.add("geeks");
        ArrLis1.add("shaan");
        ArrLis1.add("gfg");
        ArrLis1.add("programming");
  
        // print CopyOnWriteArrayList
        System.out.println("CopyOnWriteArrayList1: "
                           + ArrLis1);
  
        // create object of CopyOnWriteArrayList
        CopyOnWriteArrayList<String> ArrLis2
            = new CopyOnWriteArrayList<String>();
  
        // Add elements
        ArrLis2.add("geeks");
        ArrLis2.add("gfg");
        ArrLis2.add("qwe");
  
        // print CopyOnWriteArrayList
        System.out.println("CopyOnWriteArrayList2: "
                           + ArrLis2);
  
        // Applying the function
        ArrLis2.retainAll(ArrLis1);
  
        // print CopyOnWriteArrayLists
  
        System.out.println("After applying retainAll()"
                           + " method on ArrLis2");
        System.out.println("CopyOnWriteArrayList1: "
                           + ArrLis1);
        System.out.println("CopyOnWriteArrayList2: "
                           + ArrLis2);
    }
}

输出。

CopyOnWriteArrayList1: [geeks, shaan, gfg, programming]
CopyOnWriteArrayList2: [geeks, gfg, qwe]
After applying retainAll() method on ArrLis2
CopyOnWriteArrayList1: [geeks, shaan, gfg, programming]
CopyOnWriteArrayList2: [geeks, gfg]