Java ArrayList removeAll()方法及示例

java.util.ArrayList 类的 removeAll() 方法用于从该列表中移除包含在指定集合中的所有元素。

语法

public boolean removeAll(Collection c)

参数： 该方法接受集合c作为参数，其中包含要从这个列表中删除的元素。

返回值： 如果这个列表因调用而改变，该方法返回 true。

异常： 如果这个列表包含一个空元素，而指定的集合不允许空元素（可选），或者指定的集合是空的，这个方法会抛出 NullPointerException 。

下面是说明 removeAll() 方法的例子。

例子 1:

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

输出。

ArrayList before removeAll() operation : [1, 2, 3, 4, 5]
Collection Elements to be removed : [1, 2, 3]
ArrayList 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[] argv) throws Exception
    {
  
        try {
  
            // Creating object of ArrayList<Integer>
            ArrayList<Integer>
                arrlist1 = new ArrayList<Integer>();
  
            // Populating arrlist1
            arrlist1.add(1);
            arrlist1.add(2);
            arrlist1.add(3);
            arrlist1.add(4);
            arrlist1.add(5);
  
            // print arrlist1
            System.out.println("ArrayList before "
                               + "removeAll() operation : "
                               + arrlist1);
  
            // Creating another object of  ArrayList<Integer>
            ArrayList<Integer>
                arrlist2 = null;
  
            // print arrlist2
            System.out.println("Collection Elements"
                               + " to be removed : "
                               + arrlist2);
  
            System.out.println("\nTrying to pass "
                               + "null as a specified element\n");
  
            // Removing elements from arrlist
            // specified in arrlist2
            // using removeAll() method
            arrlist1.removeAll(arrlist2);
  
            // print arrlist1
            System.out.println("ArrayList after "
                               + "removeAll() operation : "
                               + arrlist1);
        }
  
        catch (NullPointerException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}

输出。

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

Trying to pass null as a specified element

Exception thrown : java.lang.NullPointerException