Java 中的 copy onwriterarraylist addallbsent()方法，带示例
原文:https://www . geeksforgeeks . org/copy onwriterarraylist-addallabsent-method-in-Java-with-examples/
copy onwriterarraylist的addallbsent(E E)方法按照指定集合的迭代器返回元素的顺序，将指定集合中尚未包含在该列表中的所有元素追加到该列表的末尾。
语法:
public int addAllAbsent(Collection<E> collection)
参数:该函数接受单个强制参数集合，该集合指定了列表中不存在的集合。
返回值:该函数返回一个整数值，如果列表中添加了元素，则该值为数字。
异常:如果指定的集合为空，该方法抛出空指针异常。
下面的程序说明了 addAllAbsent()函数:
程序 1:
// Java Program to illustrate the CopyOnWriteArrayList
// addAllAbsent() 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.add(2);
ArrLis.add(3);
ArrLis.add(4);
ArrLis.add(7);
// print CopyOnWriteArrayList
System.out.println("CopyOnWriteArrayList: "
+ ArrLis);
// creating an Empty Integer ArrayList
ArrayList<Integer> arr = new ArrayList<Integer>(4);
// using add() to initialize values
// [1, 2, 3, 4]
arr.add(1);
arr.add(2);
arr.add(3);
arr.add(4);
// list initially
System.out.println("The collection to be appended: "
+ arr);
// Append the list arr in the list ArrLis
// using addAllAbsent() method
System.out.println("\nNumber of elements appended"
+ " using addAllAbsent() method: "
+ ArrLis.addAllAbsent(arr));
// print CopyOnWriteArrayList
System.out.println("Modified CopyOnWriteArrayList: "
+ ArrLis);
}
}
输出:
CopyOnWriteArrayList: [2, 3, 4, 7]
The collection to be appended: [1, 2, 3, 4]
Number of elements appended using addAllAbsent() method: 1
Modified CopyOnWriteArrayList: [2, 3, 4, 7, 1]
程序 2: 演示 NullPointerException
// Java Program to illustrate the CopyOnWriteArrayList
// addAllAbsent() 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.add(2);
ArrLis.add(3);
ArrLis.add(4);
ArrLis.add(7);
// print CopyOnWriteArrayList
System.out.println("CopyOnWriteArrayList: "
+ ArrLis);
// creating a null Integer ArrayList
ArrayList<Integer> arr = null;
// list initially
System.out.println("The collection to be appended: "
+ arr);
try {
// Append the list arr in the list ArrLis
// using addAllAbsent() method
System.out.println("\nTrying to append null collection\n");
ArrLis.addAllAbsent(arr);
}
catch (Exception e) {
System.out.println(e);
}
}
}
输出:
CopyOnWriteArrayList: [2, 3, 4, 7]
The collection to be appended: null
Trying to append null collection
java.lang.NullPointerException
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