How to auto increment an alpha numeric id in Java

Question

I want to implement a functionality that auto increment an alpha numeric id in a Java program.

The ids types are Strings, have only digits and lower case latin letters, and is case insensitive.

Basically, I want a function called static String next(String id) that gives what should be the next id.

The id should increase from right to left, and new characters should be added on the left.

For example

assertEquals("1", IdUtils.next("0"));
assertEquals("a", IdUtils.next("9"));
assertEquals("10", IdUtils.next("z"));
assertEquals("10", IdUtils.next("0z"));
assertEquals("100", IdUtils.next("zz"));
assertEquals("zz1", IdUtils.next("zz0"));
assertEquals("zza", IdUtils.next("zz9"));

Thanks in advance.

it would be helpful to show us an example of the data, no? – OldProgrammer May 18 '20 at 13:09 — OldProgrammer, May 18 '20 at 13:09
Could you provide examples of inputs/outputs? – sp00m May 18 '20 at 13:09 — sp00m, May 18 '20 at 13:09

score 2 · Accepted Answer · answered May 18 '20 at 13:39

A number with digits and lower case latin letters is a base-36 number, which is an extension of base-16, also known as hex.

So to increment the base-36 number, parse it, increment it, and convert back to text.

static String next(String id) {
    return Long.toString(Math.incrementExact(Long.parseLong(id, 36)), 36);
}

Test

System.out.println(next("0"));
System.out.println(next("9"));
System.out.println(next("z"));
System.out.println(next("zzzzzz"));
System.out.println(next("dif5613ug"));
System.out.println(next("1y2p0ij32e8e6"));
System.out.println(next("1y2p0ij32e8e7")); // Long.MAX_VALUE, so will overflow

Output

1
a
10
1000000
dif5613uh
1y2p0ij32e8e7
Exception in thread "main" java.lang.ArithmeticException: long overflow

score 1 · Answer 2 · answered May 18 '20 at 13:32

1

If you're going to have an "current ID" variable that you increment, then it's better to keep that state in an AtomicLong instead of a String. It's faster, and much easier to make thread-safe:

... 
AtomicLong m_nextId = new AtomicLong();

static String next() {
    long idnum = m_nextId.getAndIncrement();
    return Long.toString(idnum,36);
}

answered May 18 '20 at 13:32

Matt Timmermans

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1

And it should be faster to compare. A long is 8 bytes, which is a lot of ids. – NomadMaker May 18 '20 at 13:43
Thank you, I will search about AtomicLong – vinicius de novaes May 18 '20 at 14:40

How to auto increment an alpha numeric id in Java

2 Answers2