Java 8: how to derive a ZoneId from ZoneOffset

Question

I was reading the API for the ZoneId class. It states that there are three tipes of ID:

1. derived from ZoneOffset

2. offset-style IDs with some form of prefix. Examples:

   ZoneId.of("GMT+2");
   ZoneId.of("UTC");
   ZoneId.of("UT+01:00");
   

3. region-based. Examples:

   ZoneId.of("Asia/Aden");
   ZoneId.of("Etc/GMT+9");
   ZoneId.of("Asia/Aqtau");
   

But what is the right syntax for the first kind? Documentation says that

[ID from ZoneOffset] consists of 'Z' and IDs starting with '+' or '-'.

What's the combination of String and ZoneOffset object I'm supposed to use to create a ZoneId of the first kind?

Answer 1

There are actually two question to be answered here

1) What is the right syntax for the first kind?

This is it:

    ZoneId z;
    z = ZoneId.of("Z"); //for UTC
    z = ZoneId.of("+02:00"); 
    z = ZoneId.of("-02:00"); 

here you can find the complete list

• Z - for UTC
• +h
• +hh
• +hh:mm
• -hh:mm
• +hhmm
• -hhmm
• +hh:mm:ss
• -hh:mm:ss
• +hhmmss
• -hhmmss

I wrongly thougt that

'Z' AND IDs starting with '+' or '-'

meant that you always needed a Z prefix (to compose something like Z+02:00). I think OR would be more appropriate.

2) What's the [needed] combination of String and ZoneOffset object?

No combination needed, you can either use a string or a ZoneOffset object:

    ZoneId z;
    z = ZoneId.of("+02:00"); 
    z = ZoneId.of(ZoneOffset.of("+02:00").getId());