Java AbstractSet removeAll()方法及示例

Java AbstractSet类的 removeAll() 方法是用来从这个集合中删除所有包含在指定集合中的元素。

语法

public boolean removeAll(Collection c)

参数： 该方法接受集合c作为参数，包含要从这个集合中移除的元素。

返回值： 如果这个集合在调用后发生了变化，该方法返回true。

异常： 该方法抛出三种类型的异常。

• UnsupportedOperationException – 如果这个集合不支持该操作，就会抛出这个异常。
• ClassCastException – 当这个集合的一个元素的类别与指定的集合不兼容时，会抛出这个异常。
• NullPointerException – 当这个集合包含一个空元素，而指定的集合不允许有空元素，或者集合是空的，就会抛出这个问题。

下面是说明removeAll()方法的例子。

程序1 :

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

输出。

AbstractSet before removeAll() operation : [1, 2, 3, 4, 5]
Collection Elements to be removed : [1, 2, 3]
AbstractSet after removeAll() operation : [4, 5]

例2： 对于NullPointerException

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

输出。

AbstractSet before removeAll() operation : [1, 2, 3, 4, 5]
Collection Elements to be removed : null
Exception thrown : java.lang.NullPointerException