Java HashSet remove() Method

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Description

The Java HashSet remove(Object o) method is used to remove the specified element from this set if it is present.

Declaration

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

public boolean remove(Object o)

Parameters

o − This is the object to be removed from this set, if present.

Return Value

The method call returns 'true' if the set contained the specified element.

Exception

NA

Removing an Entry from the HashSet of Integers Example

The following example shows the usage of Java HashSet remove() method to remove an entry 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 updated by removing an entry using remove() 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);

      // remove 2 from the set
      newset.remove(2);

      // print the set
      System.out.println("Hash set values after remove operation: "+ 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 remove operation: [1, 3]

Removing an Entry from the HashSet of Strings Example

The following example shows the usage of Java HashSet remove() method to remove an entry from the HashSet. We've created a HashSet object of String. Then few entries are added using add() method and then set is printed. Now set is updated by removing an entry using remove() 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);

      // remove "Easy" from the set
      newset.remove("Easy");

      // print the set
      System.out.println("Hash set values after remove operation: "+ 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 remove operation: [Learning, Simply]

Removing an Entry from the HashSet of Objects Example

The following example shows the usage of Java HashSet remove() method to remove an entry from the HashSet. We've created a HashSet object of Student object. Then few entries are added using add() method and then set is printed. Now set is updated by removing an entry using remove() 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);

      // remove Robert from the set
      newset.remove(new Student(2, "Robert"));

      // print the set
      System.out.println("Hash set values after remove operation: "+ 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 + " ]";
   }
   @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);
   }
   @Override
   public int hashCode() {
      return rollNo + name.hashCode();
   }
}

Output

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

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