Java Collection clear()用法及代码示例

java.util.Collection接口的clear()用于清除调用它的Collection。此方法不带任何参数，也不返回任何值。

用法:

Collection.clear()

参数：此方法不接受任何参数

返回值：此方法不返回任何值。

异常：此方法引发以下异常：

UnsupportedOperationException：如果此集合不支持添加操作

以下示例说明了Collection clear()方法：

示例1:使用LinkedList类

// Java code to illustrate boolean clear() method 
  
import java.io.*; 
import java.util.*; 
  
public class GFG { 
    public static void main(String args[]) 
    { 
  
        // creating an empty LinkedList 
        Collection<String> list = new LinkedList<String>(); 
  
        // use add() method to add elements in the list 
        list.add("Geeks"); 
        list.add("for"); 
        list.add("Geeks"); 
  
        // Output the present list 
        System.out.println("The list is: " + list); 
  
        // Clearing the LinkedList 
        list.clear(); 
  
        // printing the new list 
        System.out.println("The new List is: " + list); 
    } 
}

输出：

The list is: [Geeks, for, Geeks]
The new List is: []

示例2:使用ArrayDeque类

// Java code to illustrate clear() method 
  
import java.util.*; 
  
public class ArrayDequeDemo { 
    public static void main(String args[]) 
    { 
        // Creating an empty ArrayDeque 
        Collection<String> de_que = new ArrayDeque<String>(); 
  
        // Use add() method to add elements into the Deque 
        de_que.add("Welcome"); 
        de_que.add("To"); 
        de_que.add("Geeks"); 
        de_que.add("4"); 
        de_que.add("Geeks"); 
  
        // Displaying the ArrayDeque 
        System.out.println("ArrayDeque: " + de_que); 
  
        // Clearing the ArrayDeque 
        de_que.clear(); 
  
        // printing the new ArrayDeque 
        System.out.println("The new ArrayDeque is: "
                           + de_que); 
    } 
}

输出：

ArrayDeque: [Welcome, To, Geeks, 4, Geeks]
The new ArrayDeque is: []

示例3:使用ArrayList类

// Java code to illustrate clear() method 
  
import java.io.*; 
import java.util.*; 
  
public class ArrayListDemo { 
    public static void main(String[] args) 
    { 
  
        // create an empty array list with an initial capacity 
        Collection<Integer> arrlist = new ArrayList<Integer>(5); 
  
        // use add() method to add elements in the list 
        arrlist.add(15); 
        arrlist.add(20); 
        arrlist.add(25); 
  
        // prints all the elements available in list 
        System.out.println("ArrayList: " + arrlist); 
  
        // Clearing the ArrayList 
        arrlist.clear(); 
  
        // printing the new ArrayList 
        System.out.println("The new ArrayList is: "
                           + arrlist); 
    } 
}

输出：

ArrayList: [15, 20, 25]
The new ArrayList is: []

参考： https://docs.oracle.com/javase/9/docs/api/java/util/Collection.html#clear–

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注：本文由纯净天空筛选整理自RishabhPrabhu大神的英文原创作品 Collection clear() method in Java with Examples。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。