JAVA EXAMPLE PROGRAMS

JAVA EXAMPLE PROGRAMS

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


Description:

Below example shows how to search 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 MyObjectKeySearch {

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("Does key available? "+hm.containsKey(key));
	}
	
	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(){
		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:
item: Apple  price: 40==>Apple
item: Orange  price: 30==>Orange
item: Banana  price: 20==>Banana
Does key available? true
<< 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
When to use LinkedList or ArrayList?
Accessing elements are faster with ArrayList, because it is index based. But accessing is difficult with LinkedList. It is slow access. This is to access any element, you need to navigate through the elements one by one. But insertion and deletion is much faster with LinkedList, because if you know the node, just change the pointers before or after nodes. Insertion and deletion is slow with ArrayList, this is because, during these operations ArrayList need to adjust the indexes according to deletion or insetion if you are performing on middle indexes. Means, an ArrayList having 10 elements, if you are inserting at index 5, then you need to shift the indexes above 5 to one more.
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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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