Java HashSet clear() Method

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Description

The Java HashSet clear() method is used to remove all of the elements from this set. The set will be empty after this call returns.

Declaration

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

public void clear()

Parameters

NA

Return Value

NA

Exception

NA

Clearing a HashSet of Integers Example

The following example shows the usage of Java HashSet clear() method to remove entries from the HashSet. We've created a HashSet object of Integer. Then few entries are added using add() method and then set is printed. Now set is cleared using clear() method and printed again.

package com.tutorialspoint;

import java.util.HashSet;

public class HashSetDemo {
   public static void main(String args[]) {
      
      // create hash set
      HashSet <Integer> newset = new HashSet <>();      

      // populate hash set
      newset.add(1); 
      newset.add(2);
      newset.add(3);  

      // checking elements in hash set
      System.out.println("Hash set values: "+ newset);

      // clear the set
      newset.clear();

      // print the set
      System.out.println("Hash set values after clearing: "+ newset);
   }    
}

Output

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

Hash set values: [1, 2, 3]
Hash set values after clearing: []

Clearing a HashSet of Strings Example

The following example shows the usage of Java HashSet clear() method to remove entries from the HashSet. We've created a HashSet object of Strings. Then few entries are added using add() method and then set is printed. Now set is cleared using clear() method and printed again.

package com.tutorialspoint;

import java.util.HashSet;

public class HashSetDemo {
   public static void main(String args[]) {
      
      // create hash set
      HashSet <String> newset = new HashSet <>();      

      // populate hash set
      newset.add("Learning"); 
      newset.add("Easy");
      newset.add("Simply");  

      // checking elements in hash set
      System.out.println("Hash set values: "+ newset);

      // clear the set
      newset.clear();

      // print the set
      System.out.println("Hash set values after clearing: "+ newset);
   }    
}

Output

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

Hash set values: [Learning, Easy, Simply]
Hash set values after clearing: []

Clearing a HashSet of Objects Example

The following example shows the usage of Java HashSet clear() method to remove entries from the HashSet. We've created a HashSet object of Student objects. Then few entries are added using add() method and then set is printed. Now set is cleared using clear() method and printed again.

package com.tutorialspoint;

import java.util.HashSet;

public class HashSetDemo {
   public static void main(String args[]) {
      
      // create hash set
      HashSet <Student> newset = new HashSet <>();      

      // populate hash set
      newset.add(new Student(1, "Julie")); 
      newset.add(new Student(2, "Robert"));
      newset.add(new Student(3, "Adam"));	  

      // checking elements in hash set
      System.out.println("Hash set values: "+ newset);

      // clear the set
      newset.clear();

      // print the set
      System.out.println("Hash set values after clearing: "+ newset);
   }    
}
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.

Hash set values: [[ 1, Julie ], [ 2, Robert ], [ 3, Adam ]]
Hash set values after clearing: []