Java中的 CopyOnWriteArrayList retainAll() 方法及示例

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

句法：

public boolean retainAll(Collection col) 

参数：此方法接受一个强制参数col ，该参数属于集合类型。这是要保留在此向量中的元素的集合。

返回类型：如果由于调用 else false 导致列表完全更改，则此方法返回布尔值true。

异常：如果指定的集合为 NULL，此方法将引发 NullPointerException。

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

方案一：本方案涉及Integer类型的CopyOnArraylist的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 ArrLis1
            = new CopyOnWriteArrayList();
  
        // 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 ArrLis2
            = new CopyOnWriteArrayList();
  
        // 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]

方案二：本方案涉及String类型的CopyOnArraylist的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 ArrLis1
            = new CopyOnWriteArrayList();
  
        // 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 ArrLis2
            = new CopyOnWriteArrayList();
  
        // 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]