HashSet in Java with Example

Java Tutorial for Beginners
Java Tutorial for Beginners

HashSets and hash tables 

  • Lists allow for ordered elements, but searching them is very slow.
  • Can speed up search tremendously if you dont care about ordering.
  • Hash tables let you do this. Drawback is that you have no control over how elements are ordered.
  • hashCode() computes integer (quickly) which corresponds to position in hash table.
  • Independent of other objects in table.

HashSet  Class 

  • Hashing can be used to implement several important data structures.
  • Simplest of these is HashSet
    • add elements with add(Object) method
    • contains(Object) is redefined to first look for duplicates.
    • if duplicate exists, Object is not added
  • What determines a duplicate?
    • careful here, must redefine both hashCode() and equals(Object)!


  • Look HashSet Example
  • Play around with some additional methods.
 * HashSet in Java Example

import java.util.*;
public class app {
    public static void main(String[] args) {
        HashSet<String> name = new HashSet<String>();
        Iterator<String> itr = name.iterator();




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1 Comment

  1. :::java is a programming language and computing platform first released by Sun Microsystems in 1995. There are lots of applications and websites that will not work unless you have java installed, and more are created every day.
    java was developed by Sun microsystem as an Object oriented language for general purpose business applications. The target of java is to write a program once and then run this program on multiple operating systems.The first publicly available version of java ( java 1.0) was released in ‘95. Sun Microsystems was acquired by the Oracle Corporation in 2k10. Oracle has now the steermanship for java . In 2k06 Sun started to make java accessible under the GNU General Public License (GPL). Oracle continued this plan called Open JDK.

    Over time new improved versions of java have been released. The present version of java is java 1.9 which is also known as java 9.
    java is defined by a specification and consists of a programming language, a compiler, core libraries and a runtime ( java virtual machine) The java runtime permit software developers to write program code in other languages than the java programming language which still runs on the java virtual machine. The java platform is usually associated with the java virtual machine and the java core libraries.
    The java syntax is similar to C++. java is case-sensitive, e.g., variables called myValue andmyvalue are treated as different variables.

    Basic topics Covered in java is
    Introduction of java

    JDK vs JVM vs JVM

    Java Data Types

    Java Operators

    Java Loop Control

    Java Decision Making

    Java Array

    Java String

    Class And Object

    This Keyword in Java

    Static Keyword in Java

    Constructor in Java

    Overloading in Java

    Overriding in Java

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