Java Collection isEmpty()用法及代碼示例

java.util.Collection接口的isEmpty()用於檢查調用它的Collection是否為空。此方法不帶任何參數，也不返回任何值。

用法:

Collection.isEmpty()

參數：此方法不接受任何參數

返回值：此方法不返回任何值。

以下示例說明了Collection isEmpty()方法：

示例1:使用LinkedList類

// Java code to illustrate boolean isEmpty() 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); 
  
        // Check if list is empty 
        // using isEmpty() method 
        System.out.println("Is the LinkedList empty: "
                           + list.isEmpty()); 
  
        // Clearing the LinkedList 
        list.clear(); 
  
        // printing the new list 
        System.out.println("The new List is: " + list); 
  
        // Check if list is empty 
        // using isEmpty() method 
        System.out.println("Is the LinkedList empty: "
                           + list.isEmpty()); 
    } 
}

輸出：

The list is: [Geeks, for, Geeks]
Is the LinkedList empty: false
The new List is: []
Is the LinkedList empty: true

示例2:使用ArrayDeque類

// Java code to illustrate isEmpty() 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); 
  
        // Check if ArrayDeque is empty 
        // using isEmpty() method 
        System.out.println("Is the ArrayDeque empty: "
                           + de_que.isEmpty()); 
  
        // Clearing the ArrayDeque 
        de_que.clear(); 
  
        // printing the new ArrayDeque 
        System.out.println("The new ArrayDeque is: "
                           + de_que); 
  
        // Check if ArrayDeque is empty 
        // using isEmpty() method 
        System.out.println("Is the ArrayDeque empty: "
                           + de_que.isEmpty()); 
    } 
}

輸出：

ArrayDeque: [Welcome, To, Geeks, 4, Geeks]
Is the ArrayDeque empty: false
The new ArrayDeque is: []
Is the ArrayDeque empty: true

示例3:使用ArrayList類

// Java code to illustrate isEmpty() 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); 
  
        // Check if list is empty 
        // using isEmpty() method 
        System.out.println("Is the ArrayList empty: "
                           + arrlist.isEmpty()); 
  
        // Clearing the ArrayList 
        arrlist.clear(); 
  
        // printing the new ArrayList 
        System.out.println("The new ArrayList is: "
                           + arrlist); 
  
        // Check if ArrayList is empty 
        // using isEmpty() method 
        System.out.println("Is the ArrayList empty: "
                           + arrlist.isEmpty()); 
    } 
}

輸出：

ArrayList: [15, 20, 25]
Is the ArrayList empty: false
The new ArrayList is: []
Is the ArrayList empty: true

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

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注：本文由純淨天空篩選整理自RishabhPrabhu大神的英文原創作品 Collection isEmpty() method in Java with Examples。非經特殊聲明，原始代碼版權歸原作者所有，本譯文未經允許或授權，請勿轉載或複製。