## Saturday, September 24, 2016

### How to do customized Sorting byHashMap key or by value using Comparator - Java

This post will explain how to sort by key and sort by value using HashMap and Comparator.

Step 1: First create a Employee class which is having all the details related to Employee

/**
*
* @author rajusiva
*
*/

public class Employee {

Integer empId;
String name;
Float salary;

public Employee(Integer id,String name, Float sal){
this.empId = id;
this.name = name;
this.salary = sal;

}

@Override
public String toString() {
return "Emp Id: "+this.empId+" Name: "+this.name +" salary: " +this.salary;
}

public Integer getEmpId() {
return empId;
}
public void setEmpId(Integer empId) {
this.empId = empId;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Float getSalary() {
return salary;
}
public void setSalary(Float salary) {
this.salary = salary;
}

}

Step 2: Below is the class for sort by key and sort by value using comparator
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.TreeMap;

/** This class is used to custom sort using Comparator interface and overriding compare method.
*
* @author rajusiva
*
*/
public class CustomHashMapSort {

public static void main(String[] args) {
Map map = new HashMap();
map.put("205", new Employee(1, "siva", 75000f));
map.put("202", new Employee(2, "raju", 85000f));
map.put("203", new Employee(3, "kumar", 50000f));
map.put("204", new Employee(4, "arjun", 35000f));
map.put("200", new Employee(5, "neha", 45000f));
map.put("198", new Employee(6, "sneha", 25000f));

Map sortedMap = new TreeMap(map);
for (Iterator iterator = sortedMap.keySet().iterator(); iterator.hasNext();) {
String key = (String) iterator.next();
Employee emp = map.get(key);
System.out.println("Sort By key [" + key  +"]  [" + emp + "]");

}
System.out.println("=============================================");
HashMap sortedMapByValue = sortByValue(map);
for (Iterator iterator = sortedMapByValue.keySet().iterator(); iterator.hasNext();) {
String key = (String) iterator.next();
Employee emp = map.get(key);
System.out.println("Sort By Value by Name  Key-[ "+key  +"]  value [" + emp.getName() +"]");

}

}
/**This method will used to sort custom object value type(either empId,name, salary)
*
* @param empLoyeeMap of type Map values
* @return sorted hashmap values
*/
public static  HashMap sortByValue(Map empLoyeeMap) {

Collections.sort(list, new Comparator>() {
// sort the value using compare method and comparator
@Override
public int compare(Map.Entry value1, Map.Entry value2) {
return (value1.getValue().getName()).compareTo(value2.getValue().getName());
}
});

for (Iterator it = list.iterator(); it.hasNext();) {
Map.Entry entry = (Map.Entry) it.next();
sortedHashMap.put(entry.getKey(), entry.getValue());
}
return sortedHashMap;

}

}

output:

Sort By key [198]  [Emp Id: 6 Name: sneha salary: 25000.0]
Sort By key [200]  [Emp Id: 5 Name: neha salary: 45000.0]
Sort By key [202]  [Emp Id: 2 Name: raju salary: 85000.0]
Sort By key [203]  [Emp Id: 3 Name: kumar salary: 50000.0]
Sort By key [204]  [Emp Id: 4 Name: arjun salary: 35000.0]
Sort By key [205]  [Emp Id: 1 Name: siva salary: 75000.0]
=============================================
Sort By Value by Name  Key-[ 204]  value [arjun]
Sort By Value by Name  Key-[ 203]  value [kumar]
Sort By Value by Name  Key-[ 200]  value [neha]
Sort By Value by Name  Key-[ 202]  value [raju]
Sort By Value by Name  Key-[ 205]  value [siva]
Sort By Value by Name  Key-[ 198]  value [sneha]

Hope this will help you to understand how we can custom object sort by key and value using comparator.

#### 1 comment:

1. Sure, this solution works nicely, as I can see. But why don't you use Comparable in order to do that. It's not a controversy, just don't get it clearly and have some questions. To be frank, I'm pure newbie in Java programming and in backend at all either. I'm learning all the theory by these courses, where I can find the answer for most common topics like difference between comparable and comparator https://explainjava.com/comparable-comparator-java/ and theory here seems so content to me. So I don't understand why don't you use compatator here instead, because it seems to be easier in comparable..?