Java Hashtable contains()用法及代碼示例

Java中的java.util.Hashtable.contains(Object value)方法用於檢查Hashtable中存在的任何鍵是否正在映射特定值。

用法:

Hash_table.contains(Object value)

參數：該方法接受對象類型的一個參數值，表示要驗證其映射的哈希表的值。

返回值：如果傳遞的值由Hashtable中的任何鍵映射，則該方法返回布爾值true。

異常：如果傳遞的值為Null，則該方法將引發NullPointerException。

以下示例程序旨在說明上述方法的用法方式：
示例1:

// Java code to illustrate the contains() method 
import java.util.*; 
  
public class Hash_Table_Demo { 
    public static void main(String[] args) 
    { 
  
        // Creating an empty Hashtable 
        Hashtable<Integer, String> hash_table =  
        new Hashtable<Integer, String>(); 
  
        // Mapping string values to int keys 
        hash_table.put(10, "Geeks"); 
        hash_table.put(15, "4"); 
        hash_table.put(20, "Geeks"); 
        hash_table.put(25, "Welcomes"); 
        hash_table.put(30, "You"); 
  
        // Displaying the HashMap 
        System.out.println("Initial Table is: " + hash_table); 
  
        // Checking for the Value 'Geeks' 
        System.out.println("Is the value 'Geeks' present? " +  
        hash_table.contains("Geeks")); 
  
        // Checking for the Value 'World' 
        System.out.println("Is the value 'World' present? " +  
        hash_table.contains("World")); 
    } 
}

輸出：

Initial Table is: {10=Geeks, 20=Geeks, 30=You, 15=4, 25=Welcomes}
Is the value 'Geeks' present? true
Is the value 'World' present? false

示例2:

// Java code to illustrate the contains() method 
import java.util.*; 
  
public class Hash_Table_Demo { 
    public static void main(String[] args) 
    { 
  
        // Creating an empty Hashtable 
        Hashtable<String, Integer> hash_table =  
        new Hashtable<String, Integer>(); 
  
        // Mapping int values to string keys 
        hash_table.put("Geeks", 10); 
        hash_table.put("4", 15); 
        hash_table.put("Geeks", 20); 
        hash_table.put("Welcomes", 25); 
        hash_table.put("You", 30); 
  
        // Displaying the Hashtable 
        System.out.println("Initial Mappings are: " + hash_table); 
  
        // Checking for the Value '10' 
        System.out.println("Is the value '10' present? " +  
        hash_table.containsValue(10)); 
  
        // Checking for the Value '30' 
        System.out.println("Is the value '30' present? " +  
        hash_table.containsValue(30)); 
  
        // Checking for the Value '40' 
        System.out.println("Is the value '40' present? " +  
        hash_table.containsValue(40)); 
    } 
}

輸出：

Initial Mappings are: {You=30, Welcomes=25, 4=15, Geeks=20}
Is the value '10' present? false
Is the value '30' present? true
Is the value '40' present? false

相關用法

注：本文由純淨天空篩選整理自Chinmoy Lenka大神的英文原創作品 Hashtable contains() Method in Java。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。