Java Program to Illustrate the Use of HashCode() Method

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This is a Java Program to Illustrate the Use of HashCode() Method. The hashcode of a Java Object is simply a number, it is 32-bit signed int, that allows an object to be managed by a hash-based data structure.

We have to implement hashcode() method of a class in such way that if two objects are equals, ie compared by equal() method of that class, then those two objects must return same hash code. The below example shows how to override equals and hashcode methods. The class Price overrides equals and hashcode. If you notice the hashcode implementation, it always generates unique hashcode for each object based on their state, ie if the object state is same, then you will get same hashcode. A HashMap is used in the example to store Price objects as keys. It shows though we generate different objects, but if state is same, still we can use this as key.

Here is the source code of the Java Program to Illustrate the Use of HashCode() Method. The Java program is successfully compiled and run on a Windows system. The program output is also shown below.

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  1. import java.util.HashMap;
  2. public class HashDemo
  3. {
  4.    public static void main(String a[])
  5.    {
  6.         HashMap<Price, String> hm = new HashMap<Price, String>();
  7.         hm.put(new Price("Banana", 20), "Banana");
  8.         hm.put(new Price("Apple", 40), "Apple");
  9.         hm.put(new Price("Orange", 30), "Orange");   //creating new object to use as key to get value
  10.         Price key = new Price("Banana", 20);
  11.         System.out.println("Hashcode of the key: "+key.hashCode());
  12.         System.out.println("Value from map: "+hm.get(key));
  13.     }
  14. }
  15. class Price
  16. {
  17.     private String item;
  18.     private int price;
  19.     public Price(String itm, int pr)
  20.     {
  21.         this.item = itm;
  22.         this.price = pr;
  23.     }
  24.     public int hashCode()
  25.     {
  26.         System.out.println("In hashcode");
  27.         int hashcode = 0;
  28.         hashcode = price*20;
  29.         hashcode += item.hashCode();
  30.         return hashcode;
  31.     }
  32.     public boolean equals(Object obj)
  33.     {
  34.         System.out.println("In equals");
  35.         if (obj instanceof Price)
  36.         {
  37.             Price pp = (Price) obj;
  38.             return (pp.item.equals(this.item) && pp.price == this.price);
  39.         }
  40.         else
  41.         {
  42.             return false;
  43.         }
  44.     }
  45.     public String getItem()
  46.     {
  47.         return item;
  48.     }
  49.     public void setItem(String item)
  50.     {
  51.         this.item = item;
  52.     }
  53.     public int getPrice()
  54.     {
  55.         return price;
  56.     }
  57.     public void setPrice(int price)
  58.     {
  59.         this.price = price;
  60.     }
  61.     public String toString()
  62.     {
  63.         return "item: "+item+"  price: "+price;
  64.     }
  65. }

Output:

$ javac HashDemo.java
$ java HashDemo
 
In hashcode
In hashcode
In hashcode
In hashcode
Hashcode of the key: 1982479637
In hashcode
In equals
Value from map: Banana

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He is Linux Kernel Developer & SAN Architect and is passionate about competency developments in these areas. He lives in Bangalore and delivers focused training sessions to IT professionals in Linux Kernel, Linux Debugging, Linux Device Drivers, Linux Networking, Linux Storage, Advanced C Programming, SAN Storage Technologies, SCSI Internals & Storage Protocols such as iSCSI & Fiber Channel. Stay connected with him @ LinkedIn