在Java中生成自动增量ID

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.

Answer 1

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;  
    }
}

Answer 2

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