Java Hashtable contains()用法及代码示例

Java中的java.util.Hashtable.contains(Object value)方法用于检查Hashtable中存在的任何键是否正在映射特定值。

用法:

Hash_table.contains(Object value)

参数：该方法接受对象类型的一个参数值，表示要验证其映射的哈希表的值。

返回值：如果传递的值由Hashtable中的任何键映射，则该方法返回布尔值true。

异常：如果传递的值为Null，则该方法将引发NullPointerException。

以下示例程序旨在说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")); 
    } 
}

输出：

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)); 
    } 
}

输出：

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

相关用法

注：本文由纯净天空筛选整理自Chinmoy Lenka大神的英文原创作品 Hashtable contains() Method in Java。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。