Program: How to sort keys in TreeMap by using Comparator with user define objects?

Below example shows how to sort user defined objects by using comparator object. You can include you own custom sorting logic with compare method. By passing comparator object to the TreeMap, you can sort the keys based on the logic provided inside the compare method.

package com.java2novice.treemap;

import java.util.Comparator;
import java.util.Set;
import java.util.TreeMap;

public class MyTMCompUserDefine {

	public static void main(String a[]){
		//By using name comparator (String comparison)
		TreeMap<Empl,String> tm = new TreeMap<Empl, String>(new MyNameComp());
		tm.put(new Empl("Ram",3000), "RAM");
		tm.put(new Empl("John",6000), "JOHN");
		tm.put(new Empl("Crish",2000), "CRISH");
		tm.put(new Empl("Tom",2400), "TOM");
		Set<Empl> keys = tm.keySet();
		for(Empl key:keys){
			System.out.println(key+" ==> "+tm.get(key));
		}
		System.out.println("===================================");
		//By using salary comparator (int comparison)
		TreeMap<Empl,String> trmap = new TreeMap<Empl, String>(new MySalaryComp());
		trmap.put(new Empl("Ram",3000), "RAM");
		trmap.put(new Empl("John",6000), "JOHN");
		trmap.put(new Empl("Crish",2000), "CRISH");
		trmap.put(new Empl("Tom",2400), "TOM");
		Set<Empl> ks = trmap.keySet();
		for(Empl key:ks){
			System.out.println(key+" ==> "+trmap.get(key));
		}
	}
}

class MyNameComp implements Comparator<Empl>{

	@Override
	public int compare(Empl e1, Empl e2) {
		return e1.getName().compareTo(e2.getName());
	}
}

class MySalaryComp implements Comparator<Empl>{

	@Override
	public int compare(Empl e1, Empl e2) {
		if(e1.getSalary() > e2.getSalary()){
			return 1;
		} else {
			return -1;
		}
	}
}

class Empl{
	
	private String name;
	private int salary;
	
	public Empl(String n, int s){
		this.name = n;
		this.salary = s;
	}
	
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public int getSalary() {
		return salary;
	}
	public void setSalary(int salary) {
		this.salary = salary;
	}
	public String toString(){
		return "Name: "+this.name+"-- Salary: "+this.salary;
	}
}

Name: Crish-- Salary: 2000 ==> CRISH
Name: John-- Salary: 6000 ==> JOHN
Name: Ram-- Salary: 3000 ==> RAM
Name: Tom-- Salary: 2400 ==> TOM
===================================
Name: Crish-- Salary: 2000 ==> CRISH
Name: Tom-- Salary: 2400 ==> TOM
Name: Ram-- Salary: 3000 ==> RAM
Name: John-- Salary: 6000 ==> JOHN