用示例收集 Java 中的 isEmpty()方法
原文:https://www . geesforgeks . org/collection-isempty-method-in-Java-with-examples/
java.util.Collection 接口的 isEmpty() 用于检查调用它的 Collection 是否为空。此方法不接受任何参数，也不返回任何值。
语法:
Collection.isEmpty()
参数:此方法不接受任何参数
返回值:此方法不返回值。
以下示例说明了集合 isEmpty()方法:
示例 1: 使用链接列表类
// 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());
}
}
输出:
The list is: [Geeks, for, Geeks]
Is the LinkedList empty: false
The new List is: []
Is the LinkedList empty: true
例 2: 使用 ArrayDeque 类
// 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());
}
}
输出:
ArrayDeque: [Welcome, To, Geeks, 4, Geeks]
Is the ArrayDeque empty: false
The new ArrayDeque is: []
Is the ArrayDeque empty: true
示例 3: 使用数组列表类
// 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());
}
}
输出:
ArrayList: [15, 20, 25]
Is the ArrayList empty: false
The new ArrayList is: []
Is the ArrayList empty: true
参考:https://docs . Oracle . com/javase/9/docs/API/Java/util/collection . html # isEmpty–
版权属于：月萌API www.moonapi.com，转载请注明出处
