Sort a String array by specific String value

Question

I have a project where the main functionality is to read a .txt file into a String array and sort it by specific String value in each line. My .txt file is a list of employees with their name, salary ,and experience. Below is my examplary list:

Name: Thomas Green | Gross salary: 10 000 | Experience: 30 months
Name: Anna Lang | Gross salary: 6 000 | Experience: 12 months
Name: Micheal Holse | Gross salary: 8 000 | Experience: 27 months

Now what I want is to sort this list through first name, salary value or experience value, after using a Scanner to change this list into an array. I have read about Comparator, but couldn't find a right example. As you see, what this program has to do is to skip "Name:" value and sort it alphabetically by first name. Or skip other Strings and sort a list by the lowest salary value. The same for experience it should sort by a number of months from the lowest to the highest.

Here is what I could do until now:

import java.io.File;
import java.io.IOException;
import java.util.*;

public class SortList { 
    public static int loadInt() {
        Scanner s = new Scanner(System.in);

        if(!s.hasNextInt()) {
            s.next();
            s.nextLine();   
            return loadInt();
        }
        return s.nextInt();
    }


    public static void main (String[] args) throws IOException{
        //show the list
        String token1 = "";
        Scanner inFile1 = new Scanner (new File ("list.txt")).useDelimiter(",\\s*");

        List<String> temps = new ArrayList<String>();

        while(inFile1.hasNext()) {
            token1 = inFile1.next();
            temps.add(token1);
        }
        inFile1.close();

        String[] tempsArray = temps.toArray(new String[0]);         
        for(String s : tempsArray) {
            System.out.println(s);
        }

        //Sort the list

        System.out.println("How do you want to sort?" + "\n" + "1. By name" + "\n" + "2. By salary" + "\n" + "3. By experience");
        int b;
        b = loadInt();
        if (b == 1){
            ArrayList<String> namesList = new ArrayList<>();

            for(int i = 0; i<tempsArray.length; i++){
                namesList.add(tempsArray[i]);
            }

            Collections.sort(namesList, (name1, name5) -> name1.split(" ")[1].compareTo(name5.split(" ")[1]));

            for(String name : namesList){
                System.out.println(name);
            }

        }
        if (b == 2){
            ArrayList<String> salaryList = new ArrayList<>();

            for(int i = 0; i<tempsArray.length; i++){
                salaryList.add(tempsArray[i]);
            }

            Collections.sort(salaryList, (salary1, salary2) -> salary1.split(" ")[10].compareTo(salary2.split(" ")[10]));

            for(String salary : salaryList){
                System.out.println(salary);
            }

        }
        if (b == 3){
            ArrayList<String> experienceList = new ArrayList<>();

            for(int i = 0; i<tempsArray.length; i++){
                experienceList.add(tempsArray[i]);
            }

            Collections.sort(experienceList, (experience1, experience2) -> experience1.split(" ")[14].compareTo(experience2.split(" ")[14]));

            for(String experience : experienceList){
                System.out.println(experience);
            }
        }
    } 
}

For now my code doesn't sort the list when I enter a integer value. Is the way I'm doing that is correct? I found example of Collection through internet, but it doesn't work for me.

The real thing here is that you need a reasonable "object" model before doing anything about those various sorting things. In that sense, the answer from dimo is an absolute must for you to look into. — GhostCat
– GhostCat, Commented Dec 28, 2016 at 19:31
Thanks for explanation. But if I create object called Employee, how am I going to load the list from txt file? I'm a beginner in Java, as such I cannot imagine how to load the object from txt file. — Thomas_Bui
– Thomas_Bui, Commented Dec 29, 2016 at 5:23
Wow, spent some time to write up a answer for you. Hope that helps, as I got the vague feeling that I wont even see much upvotes for that ... — GhostCat
– GhostCat, Commented Dec 29, 2016 at 8:23

dimo414 · Accepted Answer · 2016-12-28 19:12:11Z

4

The correct thing to do is define an Employee object with firstName, lastName, salary, and experience fields. Then you can define multiple Comparator<Employee> instances which support your different sorting options. Then you can create a List<Employee> and call Collections.sort() which will sort the elements based on the ordering defined by the Comparator.

This class might look something like this:

public class Employee {
  private final String firstName;
  private final String lastName;
  private final int salary;
  private final int experience;

  // constructor, getters
}

And your Comparator might look something like this:

public class FirstNameComparator implements Comparator<Employee> {
  @Override
  public int compare(Employee e1, Employee e2) {
    return e1.getFirstName().compareTo(e2.getFirstName());
  }
}

Or in Java 8 you can use a method reference, and just pass Comparator.comparing(Employee::getFirstName) to the Comparator parameter of Collections.sort().

Then it's just a matter of reading the file and extracting the fields from each line and constructing a Employee from each one. There are many questions on this site discussing parsing data from text files if you're unsure about that part.

edited Dec 28, 2016 at 19:12

answered Dec 28, 2016 at 19:06

dimo414

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4 Comments

ifly6 Over a year ago

+1 for mentioning the Java 8 solution with Comparator.comparing. Most people don't know where to even start with implementing Comparator, so a ready-made solution is extremely helpful.

Thomas_Bui Over a year ago

Thanks for explanation, however should I create a file with a constructor or have this part implemented in my program. So the best option is to parse data into comparable fields?

dimo414 Over a year ago

I'm afraid I don't understand your questions. Classes have constructors, not files; you can define your comparators wherever you'd like - separate files, nested classes inside SortList, or even as anonymous classes / lambdas. The key point is to separate the parsing step from the sorting step. Parse the text file into a structured object, then sort those objects.

dimo414 Over a year ago

@ifly6 yep, Java 8 introduced some great improvements for Comparator. In Pre-Java-8-land Guava's Ordering and ComparisonChain classes serve a similar purpose.

Sebastian Motavita · Accepted Answer · 2016-12-28 19:09:03Z

0

The problem of your algorithm is that when you are reading from the file, the Scanner object is reading everything at once, and the ArrayList temps is getting loaded with just 1 element. Change token1 = inFile1.next(); to token1 = inFile1.nextLine();, everything else is ok.

answered Dec 28, 2016 at 19:09

Sebastian Motavita

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Comments

GhostCat · Accepted Answer · 2016-12-29 08:22:25Z

0

Further enhancing the suggestion from dimo414. As said, you create a class that contains the relevant pieces for an employee.

That class could have a constructor like

public Employee(String firstName, String lastName, int salary, int experienceInMonths)

and you would then create employees like

List<Employee> employees = new ArrayList<>();
employees.add( new Employee ("Bilbo", "Beutlin", 5, 10) );

But of course, your date is coming from a file, which you say has lines like

Name: Thomas Green | Gross salary: 10 000 | Experience: 30 months

So, what you do know:

You write code that reads that file line by line
You create a helper method that takes one such line ... and returns an Employee object for that

Like:

public Employee createEmployeeFrom(String line) {

And within that method, you simply have to parse that string and extract the relevant information. Given your format, you could do:

use String.split("\|") ... that should slice your line into three substrings
First substring would be "Name: Thomas Green" then. Here you would use String.substring() to acquire everything after ": "; giving you "Thomas Green". Then you could assume that anything after the last space is the last name; and anything before goes as first name
Then you do similar things for the parts of your input (using methods such as Integer.valueOf() to turn String numbers into int)
Finally, you make a call `return new Employee(firstNameParsedFromInput, ....

Things is: you have to separate concerns. One concern is modeling your data using an Employee class; the other concern is to parse a string to retrieve the elements that make up an Employee. And only when all of that works nicely, you then start looking into Collections.sort() and writing your own Comparator class.

answered Dec 29, 2016 at 8:22

GhostCat

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2 Comments

Thomas_Bui Over a year ago

Thanks for the input I will consider this approach when writing the Employee class.

GhostCat Over a year ago

You are very welcome. And kindly remember my answer once you reach 15 rep and upvote privileges :-)

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