Java中的 SortedSet retainAll() 方法及示例

SortedSet接口的retainAll()方法用于从这个SortedSet 中保留指定集合中包含的所有元素。

句法：

public boolean retainAll(Collection c)

参数：此方法将集合 c作为参数，其中包含要从此 SortedSet 中保留的元素。

返回值：如果此 SortedSet 因调用而更改，则此方法返回true 。

异常：如果此集合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NullPointerException 。

注意：SortedSet 中的 retainAll() 方法继承自Java中的 Set 接口。

下面是说明retainAll()方法的示例。

示例 1：

Java

// Java program to demonstrate
// retainAll() method for Sorted set
 
import java.util.*;
 
public class GFG1 {
    public static void main(String[] args)
        throws Exception
    {
 
        try {
 
            // Creating object of Set
            SortedSet arrset1
                = new TreeSet();
 
            // Populating arrset1
            arrset1.add(1);
            arrset1.add(2);
            arrset1.add(3);
            arrset1.add(4);
            arrset1.add(5);
 
            // print arrset1
            System.out.println(
                "Set before "
                + "retainAll() operation : "
                + arrset1);
 
            // Creating another object of  Set
            SortedSet arrset2
                = new TreeSet();
            arrset2.add(1);
            arrset2.add(2);
            arrset2.add(3);
 
            // print arrset2
            System.out.println(
                "Collection Elements"
                + " to be retained : "
                + arrset2);
 
            // Removing elements from arrset
            // specified in arrset2
            // using retainAll() method
            arrset1.retainAll(arrset2);
 
            // print arrset1
            System.out.println(
                "Set after "
                + "retainAll() operation : "
                + arrset1);
        }
 
        catch (NullPointerException e) {
            System.out.println(e);
        }
    }
}

输出：

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

示例 2：对于NullPointerException 。

Java

// Java program to demonstrate
// retainAll() method for Sorted set
 
import java.util.*;
 
public class GFG1 {
    public static void main(String[] args)
        throws Exception
    {
        try {
 
            // Creating object of SortedSet
            SortedSet arrset1
                = new TreeSet();
 
            // Populating arrset1
            arrset1.add(1);
            arrset1.add(2);
            arrset1.add(3);
            arrset1.add(4);
            arrset1.add(5);
 
            // print arrset1
            System.out.println(
                "Set before "
                + "retainAll() operation : "
                + arrset1);
 
            // Creating another object of Set
            SortedSet arrset2 = null;
 
            // print arrset2
            System.out.println(
                "Collection Elements "
                + "to be retained : "
                + arrset2);
 
            System.out.println(
                "\nTrying to pass "
                + "null as a "
                + "specified element\n");
 
            // Removing elements from arrset
            // specified in arrset2
            // using retainAll() method
            arrset1.retainAll(arrset2);
 
            // print arrset1
            System.out.println(
                "Set after "
                + "retainAll() operation : "
                + arrset1);
        }
 
        catch (NullPointerException e) {
            System.out.println(e);
        }
    }
}

输出：

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

Trying to pass null as a specified element

java.lang.NullPointerException

参考：https: Java Java.util.Collection)