Java中的 CopyOnWriteArrayList contains() 方法

CopyOnWriteArrayList的contains(E e)方法检查给定元素是否存在于列表中。如果元素至少出现一次，则函数返回 true，否则返回 false。

句法：

public boolean contains(Object o)

参数：该函数接受一个强制参数o ，它指定要在列表中检查其外观的元素。

返回值：如果元素在列表中至少出现一次，则该函数返回true ，否则返回 false。

下面的程序说明了上述函数：

方案一：

// Java Program to illustrate the CopyOnWriteArrayList
// contains() method in Java
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.*;
  
public class GFG {
    public static void main(String[] args)
    {
  
        // create object of CopyOnWriteArrayList
        CopyOnWriteArrayList ArrLis
            = new CopyOnWriteArrayList();
  
        // Add elements
        ArrLis.add(32);
        ArrLis.add(67);
        ArrLis.add(98);
        ArrLis.add(100);
  
        // print CopyOnWriteArrayList
        System.out.println("CopyOnWriteArrayList: " + ArrLis);
  
        // check using function
        if (ArrLis.contains(100))
            System.out.println("100 is present in the list");
        else
            System.out.println("100 is not present in the list");
  
        // check using function
        if (ArrLis.contains(20))
            System.out.println("20 is present in the list");
        else
            System.out.println("20 is not present in the list");
    }
}

输出：

CopyOnWriteArrayList: [32, 67, 98, 100]
100 is present in the list
20 is not present in the list

方案二：

// Java Program to illustrate the CopyOnWriteArrayList
// contains() method in Java
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.*;
  
public class GFG {
    public static void main(String[] args)
    {
  
        // create object of CopyOnWriteArrayList
        CopyOnWriteArrayList ArrLis
            = new CopyOnWriteArrayList();
  
        // Add elements
        ArrLis.add("gopal");
        ArrLis.add("gfg");
        ArrLis.add("jgec");
        ArrLis.add("sudo");
  
        // print CopyOnWriteArrayList
        System.out.println("CopyOnWriteArrayList: " + ArrLis);
  
        // check using function
        if (ArrLis.contains("gfg"))
            System.out.println("'gfg' is present in the list");
        else
            System.out.println("'gfg' is not present in the list");
  
        // check using function
        if (ArrLis.contains("best"))
            System.out.println("'best' is present in the list");
        else
            System.out.println("'best' is not present in the list");
    }
}

输出：

CopyOnWriteArrayList: [gopal, gfg, jgec, sudo]
'gfg' is present in the list
'best' is not present in the list

参考： https: Java/util/concurrent/CopyOnWriteArrayList.html#contains-E-