Maximum number of characters in a string in java [duplicate]

Answer 1

In principle, as Antimony has mentioned, the limit on Strings is the number of characters you can fit in an array, i.e. 2^31-1.

The amount of data that you mention is roughly in the order of 100MB: i.e. not a huge problem if you really are sticking within that order of data. If you were thinking of using 10+ times as much, you might need to start re-thinking things.

One thing you could think about doing is to try and declare your code to pass around CharSequences rather than Strings. You can't override String, but you can create your own class that implements CharSequence if you realise later down the line that doing so can buy you some optimisation (e.g. compressing the internal representation in some way).

Apart from that, I would write the code the way you intend and then profile if you actually hit upon a performance problem in practice.

Answer 2

String literals are constrained to 65535 bytes due to being stored in the constant pool. I'm not sure if there is a limit on run time strings, apart from the obvious limit of 2^31-1 due to array addressing.

Edit to clear things up: This is 65535 bytes in Modified Utf8 encoding. It's the same as normal Utf8 except that the null character is two bytes and characters outside the BMP use a surrogate pair (6 bytes instead of 4). If you're just doing ascii, then this is just one byte per character.