JAVA EXAMPLE PROGRAMS

JAVA EXAMPLE PROGRAMS

Publish Your Article Here

Program: Write a program to implement hashcode and equals.


Description:

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 know that hash code is an unique id number allocated to an object by JVM. But actually speaking, Hash code is not an unique number for an object. If two objects are equals then these two objects should return same hash code. So 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. If you are overriding hashCode you need to override equals method also.

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.


Code:
package com.java2novice.algos;

import java.util.HashMap;

public class MyHashcodeImpl {

	public static void main(String a[]){
		
		HashMap<Price, String> hm = new HashMap<Price, String>();
		hm.put(new Price("Banana", 20), "Banana");
		hm.put(new Price("Apple", 40), "Apple");
		hm.put(new Price("Orange", 30), "Orange");
		//creating new object to use as key to get value
		Price key = new Price("Banana", 20);
		System.out.println("Hashcode of the key: "+key.hashCode());
		System.out.println("Value from map: "+hm.get(key));
	}
}

class Price{
	
	private String item;
	private int price;
	
	public Price(String itm, int pr){
		this.item = itm;
		this.price = pr;
	}
	
	public int hashCode(){
		System.out.println("In hashcode");
		int hashcode = 0;
		hashcode = price*20;
		hashcode += item.hashCode();
		return hashcode;
	}
	
	public boolean equals(Object obj){
		System.out.println("In equals");
		if (obj instanceof Price) {
			Price pp = (Price) obj;
			return (pp.item.equals(this.item) && pp.price == this.price);
		} else {
			return false;
		}
	}
	
	public String getItem() {
		return item;
	}
	public void setItem(String item) {
		this.item = item;
	}
	public int getPrice() {
		return price;
	}
	public void setPrice(int price) {
		this.price = price;
	}
	
	public String toString(){
		return "item: "+item+"  price: "+price;
	}
}

Output:
In hashcode
In hashcode
In hashcode
In hashcode
Hashcode of the key: 1982479637
In hashcode
In equals
Value from map: Banana
<< Previous Program | Next Program >>
blog comments powered by Disqus

List Of All Interview Programs:

  1. How to reverse Singly Linked List?
  2. Find out duplicate number between 1 to N numbers.
  3. Find out middle index where sum of both ends are equal.
  4. Write a singleton class.
  5. Write a program to create deadlock between two threads.
  6. Write a program to reverse a string using recursive algorithm.
  7. Write a program to reverse a number.
  8. Write a program to convert decimal number to binary format.
  9. Write a program to find perfect number or not.
  10. Write a program to implement ArrayList.
  11. Write a program to find maximum repeated words from a file.
  12. Wrie a program to find out duplicate characters in a string.
  13. Write a program to find top two maximum numbers in a array.
  14. Write a program to sort a map by value.
  15. Write a program to find common elements between two arrays.
  16. How to swap two numbers without using temporary variable?
  17. Write a program to print fibonacci series.
  18. Write a program to find sum of each digit in the given number using recursion.
  19. Write a program to check the given number is a prime number or not?
  20. Write a program to find the given number is Armstrong number or not?
  21. Write a program to convert binary to decimal number.
  22. Write a program to check the given number is binary number or not?
  23. Write a program for Bubble Sort in java.
  24. Write a program for Insertion Sort in java.
  25. Write a program to implement hashcode and equals.
  26. How to get distinct elements from an array by avoiding duplicate elements?
  27. Write a program to get distinct word list from the given file.
  28. Write a program to get a line with max word count from the given file.
  29. Write a program to convert string to number without using Integer.parseInt() method.
  30. Write a program to find two lines with max characters in descending order.
  31. Write a program to find the sum of the first 1000 prime numbers.
  32. Find longest substring without repeating characters.
  33. Write a program to remove duplicates from sorted array.
  34. How to sort a Stack using a temporary Stack?
Knowledge Centre
Inner class and Anonymous class
Inner class: classes defined in other classes, including those defined in methods are called inner classes. An inner class can have any accessibility including private.

Anonymous class: Anonymous class is a class defined inside a method without a name and is instantiated and declared in the same place and cannot have explicit constructors.
Famous Quotations
Tomorrow is often the busiest day of the week.
-- Spanish Proverb

About Author

Most Visited Pages

Other Interesting Sites

Reference: Java™ Platform Standard Ed. 7 - API Specification | Java is registered trademark of Oracle.
Privacy Policy | Copyright © 2017 by Nataraja Gootooru. All Rights Reserved.