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JAVA EXAMPLE PROGRAMS

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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
<< Previous Program | Next Program >>

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
doPost Vs doGet methods
doGet() method is used to get information, while doPost() method is used for posting information. doGet() requests can't send large amount of information and is limited to 240-255 characters. However, doPost()requests passes all of its data, of unlimited length. A doGet() request is appended to the request URL in a query string and this allows the exchange is visible to the client, whereas a doPost() request passes directly over the socket connection as part of its HTTP request body and the exchange are invisible to the client.
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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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