Java AbstractSequentialList retainAll()方法及示例

java.util.AbstractSequentialList 类的 retainAll() 方法用于保留该列表中包含在指定集合中的所有元素。语法

public boolean retainAll(Collection c)

参数： 该方法接受 集合c 作为参数，其中包含要从该列表中保留的元素。

返回值： 如果该列表因调用而发生变化，则该方法返回 true 。

异常： 如果该列表包含一个空元素，而指定的集合不允许空元素（可选），或者指定的集合为空，则该方法抛出 NullPointerException 。下面是说明retainAll()方法的例子。

例 1 :

// Java program to demonstrate
// retainAll() method for Integer value
 
import java.util.*;
 
public class GFG1 {
    public static void main(String[] argv) throws Exception
    {
 
        try {
 
            // Creating object of AbstractSequentialList<Integer>
            AbstractSequentialList<Integer>
                arrlist1 = new LinkedList<Integer>();
 
            // Populating arrlist1
            arrlist1.add(1);
            arrlist1.add(2);
            arrlist1.add(3);
            arrlist1.add(4);
            arrlist1.add(5);
 
            // print arrlist1
            System.out.println("AbstractSequentialList before "
                               + "retainAll() operation : "
                               + arrlist1);
 
            // Creating another object of  AbstractSequentialList<Integer>
            AbstractSequentialList<Integer>
                arrlist2 = new LinkedList<Integer>();
            arrlist2.add(1);
            arrlist2.add(2);
            arrlist2.add(3);
 
            // print arrlist2
            System.out.println("Collection Elements"
                               + " to be retained : "
                               + arrlist2);
 
            // Removing elements from arrlist
            // specified in arrlist2
            // using retainAll() method
            arrlist1.retainAll(arrlist2);
 
            // print arrlist1
            System.out.println("AbstractSequentialList after "
                               + "retainAll() operation : "
                               + arrlist1);
        }
 
        catch (NullPointerException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}

输出

AbstractSequentialList before retainAll() operation : [1, 2, 3, 4, 5]
Collection Elements to be retained : [1, 2, 3]
AbstractSequentialList after retainAll() operation : [1, 2, 3]

例2： 对于NullPointerException

// Java program to demonstrate
// retainAll() method for Integer value
 
import java.util.*;
 
public class GFG1 {
    public static void main(String[] argv) throws Exception
    {
 
        try {
 
            // Creating object of AbstractSequentialList<Integer>
            AbstractSequentialList<Integer>
                arrlist1 = new LinkedList<Integer>();
 
            // Populating arrlist1
            arrlist1.add(1);
            arrlist1.add(2);
            arrlist1.add(3);
            arrlist1.add(4);
            arrlist1.add(5);
 
            // print arrlist1
            System.out.println("AbstractSequentialList before "
                               + "retainAll() operation : "
                               + arrlist1);
 
            // Creating another object of  AbstractSequentialList<Integer>
            AbstractSequentialList<Integer>
                arrlist2 = null;
 
            // print arrlist2
            System.out.println("Collection Elements"
                               + " to be retained : "
                               + arrlist2);
 
            System.out.println("\nTrying to pass "
                               + "null as a specified element\n");
 
            // Removing elements from arrlist
            // specified in arrlist2
            // using retainAll() method
            arrlist1.retainAll(arrlist2);
 
            // print arrlist1
            System.out.println("AbstractSequentialList after "
                               + "retainAll() operation : "
                               + arrlist1);
        }
 
        catch (NullPointerException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}

输出

AbstractSequentialList before retainAll() operation : [1, 2, 3, 4, 5]
Collection Elements to be retained : null

Trying to pass null as a specified element

Exception thrown : java.lang.NullPointerException