Sunday, 7 April 2013

TreeMap using custom object sorting

We know that by default TreeMap will sort the values using key. Suppose if we need to sort the TreeMap using object stored in key part then we need to implement the Comparator interface and we need to @Override compare() method which will sort 2 Objects of key path and will give us the sorted output. 

Below single example will show you how to use custom Object sorting in TreeMap. TreeMap will take "Worker class instance" as key and "String name" as value. Where we need to sort the values using key based on the member variables in the Worker class. 

Class "MyNameComp" which implements the Comparator interface on "Worker" class and used to sort TreeMap based on name or salary. Below example will gives you sort on salary. Suppose if we need output based on name sorted then we need to un-comment "return obj1.getName().compareTo(obj2.getName());"

public class TreeMapUsingObjectSorting {
 public static void main(String a[]){
  TreeMap<Worker,String> map = new TreeMap<Worker, String>(new MyNameComp());
  map.put(new Worker("david",5000), "david");
  map.put(new Worker("joy",2000), "joy");
  map.put(new Worker("abel",7000), "abel");
  map.put(new Worker("ruby",9000), "ruby");
  for (Map.Entry<Worker, String> entry : map.entrySet()) {
   System.out.println("KEY : "+ entry.getKey() +" \t VALUE : "+entry.getValue());

public class Worker{
    private String name;
    private int salary;
    public Worker(String name, int salary){ = name;
        this.salary = salary;
    public String getName() {
        return name;
    public void setName(String name) { = name;
    public int getSalary() {
        return salary;
    public void setSalary(int salary) {
        this.salary = salary;
    /* Called by entry.getKey() 
       Overriding toString() method from super class Object
       Since key is Object we are return our own key value
    public String toString(){
     //return super.toString();
     return "("":"+this.salary+")";

public class MyNameComp implements Comparator<Worker>{

 public int compare(Worker obj1, Worker obj2) {
  // Sort TreeMap based on name
  //return obj1.getName().compareTo(obj2.getName());
  // Sort TreeMap based on salary
  if(obj1.getSalary() > obj2.getSalary()) return 1;
  else if(obj1.getSalary() < obj2.getSalary()) return -1;
  else return 0;


KEY : (joy:2000)   VALUE : joy
KEY : (david:5000)   VALUE : david
KEY : (abel:7000)   VALUE : abel
KEY : (ruby:9000)   VALUE : ruby

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