Java Stack retainAll()用法及代码示例

java.util.Stack类的retainAll()方法用于从此堆栈中保留指定集合中包含的所有元素。

用法:

public boolean retainAll(Collection c)

参数：此方法将集合c作为包含要从此堆栈保留的元素的参数。

返回值：如果此堆栈由于调用而更改，则此方法返回true。

异常：如果此堆栈包含null元素并且指定的集合不允许null元素(可选)，或者指定的collection为null，则此方法引发NullPointerException。

以下示例说明了retainAll()方法。

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 Stack<Integer> 
            Stack<Integer> 
                stack1 = new Stack<Integer>(); 
  
            // Populating stack1 
            stack1.add(1); 
            stack1.add(2); 
            stack1.add(3); 
            stack1.add(4); 
            stack1.add(5); 
  
            // print stack1 
            System.out.println("Stack before "
                               + "retainAll() operation : "
                               + stack1); 
  
            // Creating another object of  Stack<Integer> 
            Stack<Integer> 
                stack2 = new Stack<Integer>(); 
            stack2.add(1); 
            stack2.add(2); 
            stack2.add(3); 
  
            // print stack2 
            System.out.println("Collection Elements"
                               + " to be retained : "
                               + stack2); 
  
            // Removing elements from stack 
            // specified in stack2 
            // using retainAll() method 
            stack1.retainAll(stack2); 
  
            // print stack1 
            System.out.println("Stack after "
                               + "retainAll() operation : "
                               + stack1); 
        } 
  
        catch (NullPointerException e) { 
            System.out.println("Exception thrown : " + e); 
        } 
    } 
}

输出：

Stack before retainAll() operation : [1, 2, 3, 4, 5]
Collection Elements to be retained : [1, 2, 3]
Stack 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 Stack<Integer> 
            Stack<Integer> 
                stack1 = new Stack<Integer>(); 
  
            // Populating stack1 
            stack1.add(1); 
            stack1.add(2); 
            stack1.add(3); 
            stack1.add(4); 
            stack1.add(5); 
  
            // print stack1 
            System.out.println("Stack before "
                               + "retainAll() operation : "
                               + stack1); 
  
            // Creating another object of  Stack<Integer> 
            Stack<Integer> 
                stack2 = null; 
  
            // print stack2 
            System.out.println("Collection Elements"
                               + " to be retained : "
                               + stack2); 
  
            System.out.println("\nTrying to pass "
                               + "null as a specified element\n"); 
  
            // Removing elements from stack 
            // specified in stack2 
            // using retainAll() method 
            stack1.retainAll(stack2); 
  
            // print stack1 
            System.out.println("Stack after "
                               + "retainAll() operation : "
                               + stack1); 
        } 
  
        catch (NullPointerException e) { 
            System.out.println("Exception thrown : " + e); 
        } 
    } 
}

输出：

Stack 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

相关用法

注：本文由纯净天空筛选整理自Code_r大神的英文原创作品 Stack retainAll() method in Java with Example。非经特殊声明，原始代码版权归原作者所有，本译文未经允许或授权，请勿转载或复制。