Java中的 LinkedTransferQueue retainAll() 方法及示例

Java .util.concurrent.LinkedTransferQueue 的retainAll()方法是Java中的一个内置函数，用于保留此队列中的所有元素，即指定集合和此队列共有的元素。所有其他不常见的元素都从此队列中删除。

句法：

public boolean retainAll(Collection C)

参数：此方法采用参数C ，它是包含要保留在队列中的元素的集合。

返回：如果由于调用 else false 导致队列完全改变，则该方法返回布尔值 true。

异常：此方法引发以下异常：

• ClassCastException ：如果此 Queue 的元素的类与 Passed 集合不兼容。
• NullPointerException ：如果指定的集合为 Null。

下面的程序说明了 LinkedTransferQueue 类的 retainAll()函数：

方案一：

// Java code to illustrate
// retainAll() method of LinkedTransferQueue
  
import java.util.concurrent.LinkedTransferQueue;
import java.util.*;
  
public class GFG {
    public static void main(String[] args)
        throws InterruptedException
    {
  
        // create object of LinkedTransferQueue
        LinkedTransferQueue LTQ
            = new LinkedTransferQueue();
  
        // Add numbers to end of LinkedTransferQueue
        // using add() method
        LTQ.add(3);
        LTQ.add(6);
        LTQ.add(10);
        LTQ.add(125);
        LTQ.add(205);
  
        // Print the Queue
        System.out.println("Linked Transfer Queue : "
                           + LTQ);
  
        // Get the ArrayList to be retained
        ArrayList arraylist
            = new ArrayList();
        arraylist.add(10);
        arraylist.add(100);
        arraylist.add(125);
  
        // Print ArrayList
        System.out.println("ArrayList to be retained : "
                           + arraylist);
  
        // Retaining elements from the queue
        // which are common to arraylist
        // using retainAll() method.
        LTQ.retainAll(arraylist);
  
        // Prints the Queue
        System.out.println("Linked Transfer Queue "
                           + "after retaining ArrayList : "
                           + LTQ);
    }
}

输出：

Linked Transfer Queue : [3, 6, 10, 125, 205]
ArrayList to be retained : [10, 100, 125]
Linked Transfer Queue after retaining ArrayList : [10, 125]

方案二：

// Java code to illustrate
// retainAll() method of LinkedTransferQueue
  
import java.util.concurrent.LinkedTransferQueue;
import java.util.*;
  
public class GFG {
    public static void main(String[] args)
        throws InterruptedException
    {
  
        // create object of LinkedTransferQueue
        LinkedTransferQueue LTQ
            = new LinkedTransferQueue();
  
        // Add numbers to end of LinkedTransferQueue
        // using add() method
        LTQ.add("GeeksforGeeks");
        LTQ.add("Geek");
        LTQ.add("Gfg");
        LTQ.add("Computer");
        LTQ.add("Science");
  
        // Print the Queue
        System.out.println("Linked Transfer Queue : "
                           + LTQ);
  
        // Get the ArrayList to be retained
        ArrayList arraylist
            = new ArrayList();
        arraylist.add("Gfg");
        arraylist.add("Science");
        arraylist.add("Computer");
  
        // Print ArrayList
        System.out.println("ArrayList to be retained : "
                           + arraylist);
  
        // Retaining elements from the queue
        // which are common to arraylist
        // using retainAll() method.
        LTQ.retainAll(arraylist);
  
        // Prints the Queue
        System.out.println("Linked Transfer Queue "
                           + "after retaining ArrayList : "
                           + LTQ);
    }
}

输出：

Linked Transfer Queue : [GeeksforGeeks, Geek, Gfg, Computer, Science]
ArrayList to be retained : [Gfg, Science, Computer]
Linked Transfer Queue after retaining ArrayList : [Gfg, Computer, Science]

参考： https://docs.oracle.com/javase/9/docs/api/ Java/util/concurrent/LinkedTransferQueue.html#retainAll-java.util.Collection-