TreeMap vs HashMap

CompareTreeMapHashMap.java

package com.codinko.sample;

import java.util.HashMap;
import java.util.Map.Entry;
import java.util.TreeMap;

public class CompareTreeMapHashMap {
	public static void main(String[] args) {
		Employee emp1 = new Employee("Harley", 100);
		Employee emp2 = new Employee("Peter", 100);
		Employee emp3 = new Employee("John", 200);
		Employee emp4 = new Employee("Harley", 200);
		// mapping employee and number of badges
		TreeMap<Employee, Integer> treeMap = new TreeMap<Employee, Integer>();
		treeMap.put(emp1, 1);
		treeMap.put(emp2, 2);
		treeMap.put(emp3, 3);
		treeMap.put(emp4, 4);
		
		HashMap<Employee, Integer> hashMap = new HashMap<Employee, Integer>();
		hashMap.put(emp1, 1);
		hashMap.put(emp2, 2);
		hashMap.put(emp3, 3);
		hashMap.put(emp4, 4);

		System.out.println("TreeMap auto Sorts by the batchNumber of the  Employee (key of map)");
		System.out.println("TreeMap uses compareTo() method to compare keys!!");
		System.out
				.println("--------------------------------------------------------");
		for (Entry<Employee, Integer> entry : treeMap.entrySet()) {
			System.out.println(entry.getKey() + " has " + entry.getValue()
					+ " badges ");
		}
		
		System.out.println("*********************************************************");
		System.out.println("*********************************************************");
		
		System.out.println("HashMap is driven by implementation of hashcode and equals method");
		System.out.println("--------------------------------------------------------");
		for (Entry<Employee, Integer> entry : hashMap.entrySet()) {
			System.out.println(entry.getKey() + " has " + entry.getValue()
					+ " badges ");
		}
	}
}

class Employee implements Comparable<Employee> {
	String name;
	int batchNumber;

	@Override
	public String toString() {
		return "Employee [name=" + name + ", batchNumber=" + batchNumber + "]";
	}

	Employee(String name, int batchNumber) {
		this.name = name;
		this.batchNumber = batchNumber;
	}

	@Override
	public int compareTo(Employee employee) {
		return this.batchNumber - employee.batchNumber;
	}
	
	@Override
	public int hashCode() {
		final int prime = 31;
		int result = 1;
		result = prime * result + ((name == null) ? 0 : name.hashCode());
		return result;
	}

	@Override
	public boolean equals(Object obj) {
		if (this == obj)
			return true;
		if (obj == null)
			return false;
		if (getClass() != obj.getClass())
			return false;
		Employee other = (Employee) obj;
		if (name == null) {
			if (other.name != null)
				return false;
		} else if (!name.equals(other.name))
			return false;
		return true;
	}
}

/*
Output:

TreeMap auto Sorts by the batchNumber of the  Employee (key of map)
TreeMap uses compareTo() method to compare keys!!
--------------------------------------------------------
Employee [name=Harley, batchNumber=100] has 2 badges 
Employee [name=John, batchNumber=200] has 4 badges 
*********************************************************
*********************************************************
HashMap is driven by implementation of hashcode and equals method
--------------------------------------------------------
Employee [name=Harley, batchNumber=100] has 4 badges 
Employee [name=Peter, batchNumber=100] has 2 badges 
Employee [name=John, batchNumber=200] has 3 badges 

*/