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Program: How to eliminate duplicate user defined objects as a key from LinkedHashMap?


Description:

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


Code:
package com.java2novice.linkedhashmap;

import java.util.LinkedHashMap;
import java.util.Set;

public class MyDuplicateKeyEx {

	public static void main(String a[]){
		
		LinkedHashMap<Price, String> hm = new LinkedHashMap<Price, String>();
		hm.put(new Price("Banana", 20), "Banana");
		hm.put(new Price("Apple", 40), "Apple");
		hm.put(new Price("Orange", 30), "Orange");
		printMap(hm);
		Price key = new Price("Banana", 20);
		System.out.println("Adding duplicate key...");
		hm.put(key, "Grape");
		System.out.println("After adding dulicate key:");
		printMap(hm);
	}
	
	public static void printMap(LinkedHashMap<Price, String> map){
		
		Set<Price> keys = map.keySet();
		for(Price p:keys){
			System.out.println(p+"==>"+map.get(p));
		}
	}
}

class Price{
	
	private String item;
	private int price;
	
	public Price(String itm, int pr){
		this.item = itm;
		this.price = pr;
	}
	
	public int hashCode(){
		int hashcode = 0;
		hashcode = price*20;
		hashcode += item.hashCode();
		return hashcode;
	}
	
	public boolean equals(Object obj){
		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:
item: Apple  price: 40==>Apple
item: Orange  price: 30==>Orange
item: Banana  price: 20==>Banana
Adding duplicate key...
After adding dulicate key:
item: Apple  price: 40==>Apple
item: Orange  price: 30==>Orange
item: Banana  price: 20==>Grape
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List Of All LinkedHashMap Sample Programs:

  1. LinkedHashMap basic operations
  2. How to iterate through LinkedHashMap?
  3. How to check whether the value exists or not in a LinkedHashMap?
  4. How to delete all entries from LinkedHashMap object?
  5. How to eliminate duplicate user defined objects as a key from LinkedHashMap?
  6. How to find user defined objects as a key from LinkedHashMap?
  7. How to delete user defined objects as a key from LinkedHashMap?
Knowledge Centre
Domain Naming Service(DNS)
It is very difficult to remember a set of numbers (IP address) to connect to the Internet. The Domain Naming Service(DNS) is used to overcome this problem. It maps one particular IP address to a string of characters. For example, www.java2novice.com implies com is the domain name reserved for US commercial sites, java2novice is the name of the company and www is the name of the specific computer, which is java2novice's server.
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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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