Comparing objects inside an Array for Sorting

Question

I have been trying to compare objects in an Array by one if its properties so that I can sort the objects in the Array into a descending order. Here is the sample code: The array is Candidate[][]

    System.out.println("How many positions for this election? > ");
    numberOfPositions = sc.nextInt();
    Candidate Candidate[][] = new Candidate[numberOfPositions][];
    PoliticalParty Parties[][] = new PoliticalParty[numberOfPositions][];
    for(int i=0;i<numberOfPositions;i++){
        String name;
        String politicalParty;
        System.out.println("Enter position name > ");
        position = sc.next();
        System.out.println("How many seats? > ");
        numberOfSeats = sc.nextInt();
        System.out.println("How many candidates? > ");
        numberOfCandidates = sc.nextInt();
        Candidate[i] = new Candidate[numberOfCandidates+1];
        Candidate[i].sort(votes); //<--------------------------This is what im trying//

Wherein (votes) is an int derived from a text file using this code:

System.out.println("Enter file name > ");
    filename = sc.next();
    try {
        filescan = new Scanner(new File(filename));
    } catch (FileNotFoundException ex) {
        //Logger.getLogger(Election.class.getName()).log(Level.SEVERE, null, ex);
    }
    String L = System.lineSeparator();
    filescan.useDelimiter(L);
    while (filescan.hasNext()) {
        numberOfVoters++;
        line = filescan.next();
        for(int x=0,j=0;j<line.length();j++){
            switch(line.charAt(j)){
                case ',':
                    x++;
                    break;
                case ' ':
                    break;
                default:
                    int y = line.charAt(j)-48;
                    //Integer.parseInt(line.charAt(j).toString());
                    Candidate[x][y].addVote();
                    break;
            }
        }

Wherein (vote) is encapsulated in another Class:

public class Candidate{
int votes = 0;
String politicalParty;

public Candidate(String name, String politicalParty) {
    super(name);
    this.politicalParty = politicalParty;
}

public void addVote() {
    this.votes++;
    //return votes;
}

public int getVotes() {
    return votes;
}

@Override
public String getName() {
    return getName();
}

public void displayFields(){
    System.out.println(this.getName() + " (" + getPoliticalParty() + ") - " + votes);
}

public String getPoliticalParty() {
    return politicalParty;
}

public void setPoliticalParty(String politicalParty) {
    this.politicalParty = politicalParty;
}
}

Take a look to Comparable interface docs.oracle.com/javase/7/docs/api/java/lang/Comparable.html — Averroes
– Averroes, Commented Mar 5, 2014 at 15:41

Rainbolt · Accepted Answer · 2014-03-05 16:05:51Z

Arrays have a premade sort method. The Javadoc for Arrays.sort(Object[] a) mentions a "natural ordering". The Comparable interface exists to provide the natural order.

Step 1

Apply the interface to your class.

public class Candidate implements Comparable<Candidate> {

Step 2

Implement the compareTo(Candidate c) {} method in your class.

Read the Javadoc for compareTo() contract. In general, it must return a positive, zero, or negative number if this.property is greater than, equal to, or less than c.property, respectively. property is the field upon which you are comparing.

Tip: If property is a String, you can simply reuse String's compareTo()
- return this.property.compareto(c.property);
Tip: If property is an integer (like votes), you can cleverly create a positive, zero, or negative number by taking the difference.
- return this.votes - c.votes;

Step 3

Sort your array.

Now that your object is comparable, call Collections.sort(list) if you have a Collection or Arrays.sort(list) you have an Array of objects.

Pablo Lozano · Accepted Answer · 2014-03-05 15:41:04Z

0

I recommend you to use an ArrayList to store the elements to be sorted and then you'll have 2 options: make your items Comparable (interface) or create a Comparator (interface):

public class Candidate implements Comparable<Candidate> {
    ...

public int compareTo(Candidate c) {
    ... //compare here the attributes of this and c
}

}

answered Mar 5, 2014 at 15:41

Pablo Lozano

10.4k2 gold badges43 silver badges64 bronze badges

Comments

JimmyB · Accepted Answer · 2014-03-05 15:41:41Z

0

Quick question, short answer: java.util.Arrays.sort()

answered Mar 5, 2014 at 15:41

JimmyB

12.8k2 gold badges33 silver badges47 bronze badges

2 Comments

Luiggi Mendoza Over a year ago

You missed the Comparator or impleementing Comparable.

JimmyB Over a year ago

Thought the OP would figure that one out for himself pretty quickly :)

Pavlo K. · Accepted Answer · 2014-03-05 15:46:45Z

0

Why your variable starts from capital letter? It should be like all variables from small.
You should use collections for storing custom data types, then you can easy sort it using Collections.sort(List<T> list, Comparator<? super T> c) and define your own Comparator whatever you want.

answered Mar 5, 2014 at 15:46

Pavlo K.

3711 silver badge9 bronze badges

Collectives™ on Stack Overflow

Comparing objects inside an Array for Sorting

4 Answers 4

Comments

Comments

2 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

Comments

Comments

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related