Java 中的 copy onwriterarraylist addifabsend()方法
原文:https://www . geeksforgeeks . org/copy onwriterarraylist-addifabsend-method-in-Java/
copy onwriterarraylist的addifabsend(E E)方法在列表中没有元素的情况下，将参数中传递的元素追加到列表的末尾。向列表中添加新元素时，该函数返回 true。
语法:
public boolean addIfAbsent(E e)
参数:该函数接受单个强制参数元素，该元素指定了列表中不存在的元素。
返回值:如果添加到列表中，该函数返回真。
以下程序说明了上述功能:
程序 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
程序二:
// 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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