JAVA EXAMPLE PROGRAMS

JAVA EXAMPLE PROGRAMS

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Program: How to delete user defined objects as a key from HashMap?


Description:

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


Code:
package com.java2novice.hashmap;

import java.util.HashMap;
import java.util.Set;

public class MyDeleteKeyObject {

	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");
		printMap(hm);
		Price key = new Price("Banana", 20);
		System.out.println("Deleting key...");
		hm.remove(key);
		System.out.println("After deleting key:");
		printMap(hm);
	}
	
	public static void printMap(HashMap<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
Deleting key...
After deleting key:
item: Apple  price: 40==>Apple
item: Orange  price: 30==>Orange
<< Previous Program 

List Of All HashMap Sample Programs:

  1. Basic HashMap Operations.
  2. How to iterate through HashMap?
  3. How to copy Map content to another HashMap?
  4. How to search a key in HashMap?
  5. How to search a value in HashMap?
  6. How to get all keys from HashMap?
  7. How to get entry set from HashMap?
  8. How to delete all elements from HashMap?
  9. How to eliminate duplicate user defined objects as a key from HashMap?
  10. How to find user defined objects as a key from HashMap?
  11. How to delete user defined objects as a key from HashMap?
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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