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Program: How to eliminate duplicate user defined objects from HashSet?


Description:

Below example shows how to avoid duplicate user defined objects from HashSet. You can achieve this by implementing equals and hashcode methods at the user defined objects.


Code:
package com.java2novice.hashset;

import java.util.HashSet;

public class MyDistElementEx {

	public static void main(String a[]){
		
		HashSet<Price> lhm = new HashSet<Price>();
		lhm.add(new Price("Banana", 20));
		lhm.add(new Price("Apple", 40));
		lhm.add(new Price("Orange", 30));
		for(Price pr:lhm){
			System.out.println(pr);
		}
		Price duplicate = new Price("Banana", 20);
		System.out.println("inserting duplicate object...");
		lhm.add(duplicate);
		System.out.println("After insertion:");
		for(Price pr:lhm){
			System.out.println(pr);
		}
	}
}

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
item: Apple  price: 40
item: Orange  price: 30
item: Banana  price: 20
inserting duplicate object...
In hashcode
In equals
After insertion:
item: Apple  price: 40
item: Orange  price: 30
item: Banana  price: 20
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List Of All HashSet Sample Programs:

  1. Basic HashSet Operations.
  2. How to iterate through HashSet?
  3. How to copy Set content to another HashSet?
  4. How to delete all elements from HashSet?
  5. How to copy all elements from HashSet to an array?
  6. How to compare two sets and retain elements which are same on both sets?
  7. How to eliminate duplicate user defined objects from HashSet?
  8. How to find user defined objects from HashSet?
  9. How to delete user defined objects from HashSet?
Knowledge Centre
Interface and its usage
Interface is similar to a class which may contain method's signature only but not bodies and it is a formal set of method and constant declarations that must be defined by the class that implements it. Interfaces are useful for declaring methods that one or more classes are expected to implement, capturing similarities between unrelated classes without forcing a class relationship and determining an object's programming interface without revealing the actual body of the class.
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About Author

I'm Nataraja Gootooru, programmer by profession and passionate about technologies. All examples given here are as simple as possible to help beginners. The source code is compiled and tested in my dev environment.

If you come across any mistakes or bugs, please email me to [email protected].

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Reference: Java™ Platform Standard Ed. 7 - API Specification | Java™ Platform Standard Ed. 8 - API Specification | Java is registered trademark of Oracle.
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