Java Hashtable clear() Method

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Description

The Java Hashtable clear() method is used to clear this hashtable so that it contains no keys.

Declaration

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

public void clear()

Parameters

NA

Return Value

NA

Exception

NA

Clearing a HashTable of Integer, Integer Pair Example

The following example shows the usage of Java Hashtable clear() method to clear a Hashtable. We've created a Hashtable object of Integer,Integer pairs. Then few entries are added, table is printed. Using clear() method, table is cleared and printed again.

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);

      // clear hash table
      hashtable.clear();

      System.out.println("Hashtable elements after clear: " + hashtable);
   }    
}

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 elements after clear: {}

Clearing a HashTable of Integer, String Pair Example

The following example shows the usage of Java Hashtable clear() method to clear a Hashtable. We've created a Hashtable object of Integer,String pairs. Then few entries are added, table is printed. Using clear() method, table is cleared and printed again.

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);

      // clear hash table
      hashtable.clear();

      System.out.println("Hashtable elements after clear: " + hashtable);
   }    
}

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 elements after clear: {}

Clearing a HashTable of Integer, Object Pair Example

The following example shows the usage of Java Hashtable clear() method to clear a Hashtable. We've created a Hashtable object of Integer,Student pairs. Then few entries are added, table is printed.

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);

      // clear hash table
      hashtable.clear();

      System.out.println("Hashtable elements after clear: " + hashtable);
   }    
}
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 + " ]";
   }
}

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 elements after clear: {}