Java中的 ArrayList removeAll() 方法及示例

Java.util.ArrayList类的removeAll()方法用于从此列表中删除指定集合中包含的所有元素。

句法：

public boolean removeAll(Collection c)

参数：此方法将集合 c作为参数，其中包含要从此列表中删除的元素。

返回值：如果此列表因调用而更改，则此方法返回true 。

异常：如果此列表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，则此方法将引发NullPointerException 。

下面是说明removeAll()方法的示例。

示例 1：

Java

// 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
            ArrayList
                arrlist1 = new ArrayList();
  
            // 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
            ArrayList
                arrlist2 = new ArrayList();
            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]

示例 2：对于NullPointerException

Java

// 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
            ArrayList
                arrlist1 = new ArrayList();
  
            // 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
            ArrayList
                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