Using TreeMap to sort User-defined Objects in Java

Given example shows how to sort user defined objects TreeMap, you can sort the keys based on the logic provided inside the method.
Given a record of employees name and salary as positive integer, it is required to sort the records on the basis of employee salary, using TreeMap in Java. If salary is same, then use employee name for comparison.

Examples:

Input : xbnnskd 100 geek 50
Output : geek 50 xbnnskd 100

Input : shyam 50 ram 50
Output : ram 50 shyam 50
Explanation : 
As both the employees have equal pay, 
sorting is done on the basis of employee's name.

Approach:

1. Traverse through the string 
   and map the employee's salary(S)
   with the list of employee names having salary S.
2. Use a TreeMap to have 
   keys(Employee's Salary) in a sorted manner.
3. Now, Traverse through the map 
   and print the sorted records.

Below is the implementation of above approach:

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// Java program to print employees
// records in a sorted manner
  
import java.io.*;
import java.util.*;
  
public class GFG {
  
    // Function to sort the records
    static void sortRecords(String records)
    {
  
        // split the string
        // on the basis of delimiter space(" ")
        String[] rec = records.split(" ");
  
        // Create a Treemap to store
        // employee's salary with employee's name
        Map<Integer, ArrayList<String> > map = new TreeMap<>();
  
        // Traverse the records array
        // and store values in map
        for (int i = 1; i < rec.length; i += 2) {
  
            // Converting String to integer
            int sal = Integer.parseInt(rec[i]);
  
            String name = rec[i - 1];
  
            if (map.containsKey(sal)) {
  
                ArrayList<String> al = map.get(sal);
                al.add(name);
  
                // Sorting list of employees having Salary sal
                Collections.sort(al);
                map.remove(sal);
                map.put(sal, al);
            }
            else {
                ArrayList<String> al = new ArrayList<>();
                al.add(name);
                map.put(sal, al);
            }
        }
  
        // Traversing the map
        // to print the sorted records
        for (Map.Entry<Integer,
                       ArrayList<String> >
                 entry : map.entrySet()) {
  
            ArrayList<String> al1 = entry.getValue();
  
            for (int i = 0; i < al1.size(); i++)
                System.out.print(al1.get(i) + " "
                                 + entry.getKey() + " ");
        }
    }
  
    // Driver code
    public static void main(String args[])
    {
       String records = "Harsh 100 Neha 100 Neha 20 Samay 600 Karan 50";
        // Calling function to sort the records
        sortRecords(records);
    }
}

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Output:

Neha 20 Karan 50 Harsh 100 Neha 100 Samay 600


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