CODEWITHSUNDEEP
java
sander
sander

Reputation: 1654

Auto-Increment id in java

Team one and Team two have both id 0? What am I doing wrong? I'm just trying to auto increment the id every time a new object is made.

This is code from Team.java

public class Team{
    private int teamId;

    public Team(){
        this.teamId= teamId++;
    }
    public void printTeamId(){
        System.out.println(this.teamId);
    }
}

This is code from Main.java

public class Main {

    public static void main(String[] args) {

    Team one= new Team();
    Team two= new Team();
        one.printTeamId();
        two.printTeamId();
    }
}

Upvotes: 3

Views: 18488

Answers (3)

Peter B
Peter B

Reputation: 1581

You need an extra static variable to store the amount of teams. static means that all the objects share this variable. Every team has it's own variable teamId, but share the variable teamIdCounter

public class Team{
    private int teamId;
    private static int teamIdCounter = 0;

    public Team(){
        this.teamId= teamIdCounter++;
    }
    public void printTeamId(){
        System.out.println(this.teamId);
    }
}

If you are using multiple threads, check the other answers on how to use AtomicInteger to count your objects threads-safe.

Upvotes: 13

Gatusko
Gatusko

Reputation: 2598

About the static variable is ok but if you want to be thread safe use Atomic Integer.

public class Team{
    private int teamId;
    private static AtomicInteger atomicInteger = new AtomicInteger(0);

    public Team(){
        this.teamId= atomicInteger.incrementAndGet();
    }
    public void printTeamId(){
        System.out.println(this.teamId);
    }
}

This will make a thread safe counter instead a static counter that will not be thread safe.

Upvotes: 6

Shreshth Neema
Shreshth Neema

Reputation: 119

Make your teamId variable static & initialize it with some integer value (recommended is -1).

Using initial value -1 cause first teamId = 0.

Upvotes: -2

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