Java教程

Java Vector isEmpty()

Java Vector类的 isEmpty()方法用于检查此Vector是否不包含任何组件。如果向量为空，则返回true，否则返回false。

语法

以下是 isEmpty()方法的声明:

Public boolean isEmpty()

参数

此方法不接受任何参数。

isEmpty()方法仅当此向量没有任何分量时返回true，否则返回false。

异常

兼容性版本

Java 1.2及更高版本

示例1

import java.util.*;
public class VectorIsEmptyExample1 {  
  public static void main(String arg[]) { 
      //Create an empty vector
      Vector < String > vec = new Vector < String > ();
      //Add elements in the vector
      vec.add("Java");
      vec.add("Ruby");
      vec.add("Android");
      vec.add("Python");
      //Displaying the Vector
          System.out.println("Vector:  " + vec);
          //Verifying if the Vector is empty or not
          System.out.println("Is the Vector empty? = " +vec.isEmpty());
          //Clear the Vector
          vec.clear(); 
          //Displaying the Vector Again
          System.out.println("Vector after clear(): " +vec); 
          //Verifying if the Vector is empty or not
          System.out.println("Is the Vector empty? = " +vec.isEmpty());
      }            
}

输出:

Vector:  [Java, Ruby, Android, Python]
Is the Vector empty? = false
Vector after clear(): []
Is the Vector empty? = true

示例2

import java.util.*;
public class VectorIsEmptyExample2 {  
  public static void main(String arg[]) { 
    //Create an empty Vector with initial capacity of 5      
    Vector<Integer> vecObject = new Vector<Integer>(5);  
    //Display the Vector
            System.out.println("Vector: " +vecObject);
            //Verifying if the Vector is empty or not
            System.out.println("Is the Vector empty? = " +vecObject.isEmpty());       
        }            
}

输出:

Vector: []
Is the Vector empty? = true

示例3

import java.util.*;
public class VectorIsEmptyExample3 {  
  public static void main(String arg[]) { 
      //Create an empty Vector      
      Vector < String > colors = new Vector < String > ();
      //Add color elements in the vector
          colors.add("Red");
          colors.add("Green");
          colors.add("Blue");
          colors.add("Pink");
          //Test the vector if it has no components
          System.out.println("Vector isEmpty() before? " +colors.isEmpty());
          //Remove all elements from the vector
          colors.removeAllElements();
          //Again test the vector if it has no components
          System.out.println("Vector isEmpty() after ? " +colors.isEmpty());      
      }            
}

输出:

Vector isEmpty() before? false
Vector isEmpty() after ? true

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