Why the constructor is default while creating singleton?

Question

Why is the default constructor used in this method?

public static TicketCounterSingle getInstance() {
    if (instance == null) {
        instance = new TicketCounterSingle();
    }
    return instance;
}

This is the full class:

public class TicketCounterSingle {
    private static TicketCounterSingle instance;

    String Name;
    int avail;

    private TicketCounterSingle(String Name, int avail) {
        this.avail = avail;
        this.Name = Name;
    }

    public String getName() {
        return Name;
    }

    public synchronized boolean bookTicket(int ticket) {
        if (avail >= ticket) {
            avail = avail - ticket;
            return true;
        } else {
            return false;
        }
    }

    public static TicketCounterSingle getInstance() {
        if (instance == null) {
            instance = new TicketCounterSingle();
        }
        return instance;
    }
}

Maybe there is just a default constructor? Could you show us the entire class **and** explain in detail what you cannot understand, please? Thanks... — deHaar, Nov 06 '19 at 13:24

score 0 · Answer 1 · edited Feb 14 '21 at 09:50

0

Your code will not compile, because there is no default constructor.

TicketCounterSingle() {}

in your class.

There is a parameterized one:

private TicketCounterSingle(String Name, int avail) {
    this.avail = avail;
    this.Name = Name;
}

That means the default constructor will not be provided automatically, and you either have to provide a default constructor or call the parameterized one in a parameterized getInstance(String name, int avail) method:

public static TicketCounterSingle getInstance(String name, int avail) {
    if (instance == null) {
        instance = new TicketCounterSingle(String name, int avail);
    }
    return instance;
}

edited Feb 14 '21 at 09:50

Mark Rotteveel

100,966
191
140
197

answered Nov 06 '19 at 13:51

deHaar

17,687
10
38
51

The constructor TicketCounterSingle() is undefined compilation error – Nisha Nov 06 '19 at 14:27
@Nisha That's exactly what I tried to answer... Either define one or use the one that has arguments. – deHaar Nov 06 '19 at 14:28

Why the constructor is default while creating singleton?

1 Answers1