Java Hashtable contains() Method

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Description

The Java Hashtable contains(Object value) method is used to test if some key maps into the specified value in this hashtable.

Declaration

Following is the declaration for java.util.Hashtable.contains() method.

public boolean contains(Object value)

Parameters

value − This is the a value to be searched.

Return Value

The method call returns true if and only if some key maps to the value argument in this hashtable.

Exception

NullPointerException − This is thrown if the value is null.

Checking if Value Exists in a HashTable of Integer, Integer Pair Example

The following example shows the usage of Java Hashtable contains() method to check if a value is present in a Hashtable or not. We've created a Hashtable object of Integer,Integer pairs. Then few entries are added, table is printed and using contains() we're checking about two values in the table.

package com.tutorialspoint;

import java.util.Hashtable;

public class HashtableDemo {
   public static void main(String args[]) {
      
      // create hash table
      Hashtable<Integer,Integer> hashtable = new Hashtable<>();

      // populate hash table
      hashtable.put(1, 1);
      hashtable.put(2, 2);
      hashtable.put(3, 3); 

      System.out.println("Initial table elements: " + hashtable);
      System.out.println("Hashtable contains 2 as value: " + hashtable.contains(2));
      System.out.println("Hashtable contains 4 as value: " + hashtable.contains(4));
   }    
}

Output

Let us compile and run the above program, this will produce the following result.

Initial table elements: {3=3, 2=2, 1=1}
Hashtable contains 2 as value: true
Hashtable contains 4 as value: false

Checking if Value Exists in a HashTable of Integer, String Pair Example

The following example shows the usage of Java Hashtable contains() method to check if a value is present in a Hashtable or not. We've created a Hashtable object of Integer,String pairs. Then few entries are added, table is printed and using contains() we're checking about two values in the table.

package com.tutorialspoint;

import java.util.Hashtable;

public class HashtableDemo {
   public static void main(String args[]) {
      
      // create hash table
      Hashtable<Integer,String> hashtable = new Hashtable<>();

      // populate hash table
      hashtable.put(1, "tutorials");
      hashtable.put(2, "point");
      hashtable.put(3, "is best"); 

      System.out.println("Initial table elements: " + hashtable);
      System.out.println("Hashtable contains tutorials as value: " + hashtable.contains("tutorials"));
      System.out.println("Hashtable contains java as value: " + hashtable.contains("java"));
   }    
}

Output

Let us compile and run the above program, this will produce the following result.

Initial table elements: {3=is best, 2=point, 1=tutorials}
Hashtable contains tutorials as value: true
Hashtable contains java as value: false

Checking if Value Exists in a HashTable of Integer, Object Pair Example

The following example shows the usage of Java Hashtable contains() method to check if a value is present in a Hashtable or not. We've created a Hashtable object of Integer,Student pairs. Then few entries are added, table is printed and using contains() we're checking about two values in the table.

package com.tutorialspoint;

import java.util.Hashtable;

public class HashtableDemo {
   public static void main(String args[]) {
      
      // create hash table
      Hashtable<Integer,Student> hashtable = new Hashtable<>();

      // populate hash table
      hashtable.put(1, new Student(1, "Julie"));
      hashtable.put(2, new Student(2, "Robert"));
      hashtable.put(3, new Student(3, "Adam"));

      System.out.println("Initial table elements: " + hashtable);
      System.out.println("Hashtable contains Robert as value: " + hashtable.contains(new Student(2, "Robert")));
      System.out.println("Hashtable contains Jene as value: " + hashtable.contains(new Student(4, "Jene")));
   }    
}
class Student {
   int rollNo;
   String name;

   Student(int rollNo, String name){
      this.rollNo = rollNo;
      this.name = name;
   }

   @Override
   public String toString() {
      return "[ " + this.rollNo + ", " + this.name + " ]";
   }
   @Override
   public boolean equals(Object obj) {
      if(obj == null) return false;
      Student s = (Student)obj;
      return this.rollNo == s.rollNo && this.name.equalsIgnoreCase(s.name);
   }
}

Output

Let us compile and run the above program, this will produce the following result.

Initial table elements: {3=[ 3, Adam ], 2=[ 2, Robert ], 1=[ 1, Julie ]}
Hashtable contains Robert as value: true
Hashtable contains Jene as value: false