Program: How to sort a TreeSet with user defined objects?

To implement your own sorting functionality with TreeSet on user defined objects, you have to pass Comparator object along with TreeSet constructor call. The Comparator implementation holds the sorting logic. You have to override compare() method to provide the sorting logic on user defined objects. Below example shows how to sort TreeSet using comparator with user defined objects.

package com.java2novice.treeset;

import java.util.Comparator;
import java.util.TreeSet;

public class MyCompUserDefine {

	public static void main(String a[]){
		//By using name comparator (String comparison)
		TreeSet<Empl> nameComp = new TreeSet<Empl>(new MyNameComp());
		nameComp.add(new Empl("Ram",3000));
		nameComp.add(new Empl("John",6000));
		nameComp.add(new Empl("Crish",2000));
		nameComp.add(new Empl("Tom",2400));
		for(Empl e:nameComp){
			System.out.println(e);
		}
		System.out.println("===========================");
		//By using salary comparator (int comparison)
		TreeSet<Empl> salComp = new TreeSet<Empl>(new MySalaryComp());
		salComp.add(new Empl("Ram",3000));
		salComp.add(new Empl("John",6000));
		salComp.add(new Empl("Crish",2000));
		salComp.add(new Empl("Tom",2400));
		for(Empl e:salComp){
			System.out.println(e);
		}
	}
}

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
Name: John-- Salary: 6000
Name: Ram-- Salary: 3000
Name: Tom-- Salary: 2400
===========================
Name: Crish-- Salary: 2000
Name: Tom-- Salary: 2400
Name: Ram-- Salary: 3000
Name: John-- Salary: 6000