Generate auto increment id in java

Question

I have already asked this before how to generate auto increment ID Generate auto increment number by using Java.

I have used below code:

private static final AtomicInteger count = new AtomicInteger(0);   
uniqueID = count.incrementAndGet();

The previous code working fine but the problem is count static variable. For this static its never start to 0 again, its always start with the last increment id. That is the issue.

Is there any alternative way except AtomicInteger?

Another issue is that I am working on GWT so AtomicInteger is not available in GWT.

So I have to find another way to do that.

`its never start to 0 again, its always start with the last increment id` - isn't that the subject of an auto-increment? Or are you asking how you can restart at `0`? — Andreas Fester, Feb 02 '16 at 06:24
Did you try `count.set(0)`? https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/atomic/AtomicInteger.html#set-int- — Andreas Fester, Feb 02 '16 at 06:28
How do you know that this time it is supposed to be 0 and not incrememented by 1? — Limit, Feb 02 '16 at 06:28
Why? You should be doing this sort of thing with a database. — user207421, Feb 02 '16 at 07:34
@EJP I want to do this programmatically . Another thing is that I am not using any database. — Shiladittya Chakraborty, Feb 02 '16 at 07:40
You want a **uniqueId**. So why do you want to restart from 0? Then, if you do the id is not **unique** anymore! — Olivier Grégoire, Feb 02 '16 at 10:03

Kostas Kryptos · Answer 1 · 2016-02-02T07:07:53.297

AtomicInteger is a "signed" integer. It will increase till Integer.MAX_VALUE; then, due to integer overflow, you expect to get Integer.MIN_VALUE.

Unfortunately, most of the thread safe methods in AtomicInteger are final, including incrementAndGet(), so you cannot override them.

But you could create a custom class that wraps an AtomicInteger and you just create synchronized methods according to your needs. For instance:

public class PositiveAtomicInteger {

    private AtomicInteger value;

    //plz add additional checks if you always want to start from value>=0
    public PositiveAtomicInteger(int value) {
        this.value = new AtomicInteger(value);
    }

    public synchronized int incrementAndGet() {
        int result = value.incrementAndGet();
        //in case of integer overflow
        if (result < 0) {
            value.set(0);
            return 0;
        }
        return result;  
    }
}

score 0 · Answer 2 · answered Feb 02 '16 at 06:57

0

private static AtomicInteger count = new AtomicInteger(0);    
count.set(0);    
uniqueID = count.incrementAndGet();

answered Feb 02 '16 at 06:57

Rey

7
2

I don't know if you saw OP's edit: *"Is there any alternative way except `AtomicInteger`?"* Also, code only answers with no explanations are usually frowned upon. – Jonny Henly Feb 02 '16 at 07:00

Generate auto increment id in java

2 Answers2