如果列表中不存在该参数,则CopyOnWriteArrayList的addIfAbsent(E e)方法会将在参数中传递的元素附加到列表的末尾。向列表中添加新元素时,该函数返回true。
用法:
public boolean addIfAbsent(E e)
参数:该函数接受单个强制性参数element ,该元素指定要添加到列表的元素(如果不存在)。
返回值:如果将其添加到列表,则该函数返回true。
以下示例程序旨在说明上述函数:
示例1:
// Java Program to illustrate the CopyOnWriteArrayList
// addIfAbsent(element) 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<Integer> ArrLis
= new CopyOnWriteArrayList<Integer>();
// Add elements
ArrLis.addIfAbsent(2);
ArrLis.addIfAbsent(3);
ArrLis.addIfAbsent(4);
ArrLis.addIfAbsent(7);
// print CopyOnWriteArrayList
System.out.println("CopyOnWriteArrayList: "
+ ArrLis);
System.out.println("On adding 4 it returns "
+ ArrLis.addIfAbsent(4) + " as it is present");
}
}
输出:
CopyOnWriteArrayList: [2, 3, 4, 7] On adding 4 it returns false as it is present
示例2:
// Java Program to illustrate the CopyOnWriteArrayList
// addIfAbsent(element) 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<String> ArrLis
= new CopyOnWriteArrayList<String>();
// Add elements
ArrLis.addIfAbsent("gopal");
ArrLis.addIfAbsent("gfg");
ArrLis.addIfAbsent("jgec");
ArrLis.addIfAbsent("sudo");
// print CopyOnWriteArrayList
System.out.println("CopyOnWriteArrayList: " + ArrLis);
System.out.println("On adding 'sudo' it returns "
+ ArrLis.addIfAbsent("sudo") + " as it is present");
}
}
输出:
CopyOnWriteArrayList: [gopal, gfg, jgec, sudo] On adding 'sudo' it returns false as it is present
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注:本文由纯净天空筛选整理自gopaldave大神的英文原创作品 CopyOnWriteArrayList addIfAbsent() method in Java。非经特殊声明,原始代码版权归原作者所有,本译文未经允许或授权,请勿转载或复制。