Java 中的抽象顺序列表 retainAll()方法，示例
原文:https://www . geeksforgeeks . org/abstractsequentialist-retainnal-method-in-Java-with-example/
Java . util . abstractsequentialist类的retainnal()方法用于从该列表中保留指定集合中包含的所有元素。
语法:
public boolean retainAll(Collection c)
参数:该方法将集合 c 作为包含要从该列表中保留的元素的参数。
返回值:如果该列表因调用而改变，则该方法返回真。
异常:如果此列表包含空元素，并且指定的集合不允许空元素(可选)，或者指定的集合为空，则此方法抛出空指针异常。
以下是说明retainal()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 retaind : "
+ 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);
}
}
}
Output:
AbstractSequentialList before retainAll() operation : [1, 2, 3, 4, 5]
Collection Elements to be retaind : [1, 2, 3]
AbstractSequentialList after retainAll() operation : [1, 2, 3]
示例 2: 适用于空指针异常
// 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 retaind : "
+ 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);
}
}
}
Output:
AbstractSequentialList before retainAll() operation : [1, 2, 3, 4, 5]
Collection Elements to be retaind : null
Trying to pass null as a specified element
Exception thrown : java.lang.NullPointerException
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