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📜  Java中的 AbstractSet retainAll() 方法与示例

📅  最后修改于: 2022-05-13 01:54:50.695000             🧑  作者: Mango

Java中的 AbstractSet retainAll() 方法与示例

Java.util.AbstractSet类的retainAll()方法用于从该集合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,其中包含要从该集合中保留的元素。

返回值:如果此集合因调用而更改,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

下面是说明retainAll()方法的示例。

示例 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 AbstractSet
            AbstractSet
                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("AbstractSet before "
                               + "retainAll() operation : "
                               + arrset1);
  
            // Creating another object of  AbstractSet
            AbstractSet
                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("AbstractSet after "
                               + "retainAll() operation : "
                               + arrset1);
        }
  
        catch (NullPointerException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}
输出:
AbstractSet before retainAll() operation : [1, 2, 3, 4, 5]
Collection Elements to be retained : [1, 2, 3]
AbstractSet after retainAll() operation : [1, 2, 3]

示例 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 AbstractSet
            AbstractSet
                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("AbstractSet before "
                               + "retainAll() operation : "
                               + arrset1);
  
            // Creating another object of  AbstractSet
            AbstractSet
                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("AbstractSet after "
                               + "retainAll() operation : "
                               + arrset1);
        }
  
        catch (NullPointerException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}
输出:
AbstractSet 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