Java中的CopyOnWriteArrayList removeAll()方法及示例

CopyOnWriteArrayList类中的removeAll()方法可以从调用对象的CopyOnArrayList中删除指定集合中包含的所有元素。

语法：

public boolean removeAll(Collection collection)

参数：该方法仅接受一个参数collection，即要从调用对象中删除的集合。

返回值：该方法返回一个布尔值。如果此删除操作成功，则返回true。

异常：该方法会抛出以下异常：

• ClassCastException：如果此列表元素的类与指定的集合不兼容。
• NullPointerException： 如果指定的集合为null，或者如果此列表包含空元素且指定的集合不允许空元素。

以下示例说明了removeAll()方法：

示例1：

// Java program to demonstrate removeAll() method
  
import java.util.ArrayList;
import java.util.concurrent.CopyOnWriteArrayList;
  
public class Demo {
  
    public static void main(String args[])
    {
  
        // Get the CopyOnWriteArrayList
        CopyOnWriteArrayList<String> wishlist
            = new CopyOnWriteArrayList<>();
  
        // Add the elements in the CopyOnWriteArrayList
        wishlist.add("TV");
        wishlist.add("computer");
        wishlist.add("play station");
        wishlist.add("mobile");
        wishlist.add("smart watch");
  
        // Print the CopyOnWriteArrayList
        System.out.println("CopyOnWriteArrayList: \n"
                           + wishlist);
  
        // Get the collection to be removed
        ArrayList<String> checkList
            = new ArrayList<>();
  
        checkList.add("play station");
        checkList.add("TV");
        checkList.add("mobile");
  
        System.out.println("\nCollection to be removed:\n"
                           + checkList);
  
        // Remove the collection from CopyOnWriteArrayList
        // using removeAll() method
        wishlist.removeAll(checkList);
  
        // Print the CopyOnWriteArrayList after removal
        System.out.println("\nAfter removal of collection"
                           + " from CopyOnWriteArrayList:\n"
                           + wishlist);
    }
}

CopyOnWriteArrayList: 
[TV, computer, play station, mobile, smart watch]

Collection to be removed:
[play station, TV, mobile]

After removal of collection from CopyOnWriteArrayList:
[computer, smart watch]

示例2：演示NullPointerException

// 展示 removeAll() 方法的 Java 程序
  
import java.util.ArrayList;
import java.util.concurrent.CopyOnWriteArrayList;
  
public class Demo {
  
    public static void main(String args[])
    {
  
        // 获取 CopyOnWriteArrayList
        CopyOnWriteArrayList<String> wishlist
            = new CopyOnWriteArrayList<>();
  
        // 向 CopyOnWriteArrayList 添加元素
        wishlist.add("电视");
        wishlist.add("电脑");
        wishlist.add("PlayStation 游戏机");
        wishlist.add("手机");
        wishlist.add("智能手表");
  
        // 输出 CopyOnWriteArrayList
        System.out.println("CopyOnWriteArrayList: \n"
                           + wishlist);
  
        // 获取要移除的集合
        ArrayList<String> checkList
            = null;
        System.out.println("\n要移除的集合："
                           + checkList);
  
        try {
  
            // 使用 removeAll() 方法从 CopyOnWriteArrayList 移除集合
            wishlist.removeAll(checkList);
        }
        catch (Exception e) {
  
            // 输出 Exception
            System.out.println("\n从 CopyOnWriteArrayList 移除 null "
                               + "时出现异常：\n"
                               + e);
        }
    }
}

CopyOnWriteArrayList: 
[电视, 电脑, PlayStation 游戏机, 手机, 智能手表]

要移除的集合：null

从 CopyOnWriteArrayList 移除 null 时出现异常：
java.lang.NullPointerException