I wrote some stress-test cases for a Java library recently which involved 1-GB and 2-GB strings. On the surface, a java.lang.String should be a wrapper around

I wrote some stress-test cases for a Java library recently which involved 1-GB and 2-GB strings. On the surface, a java.lang.String should be a wrapper around a char[], whose maximum length is Integer.MAX_VALUE = 2 147 483 647. This is roughly how older implementations of JDK did things. But as of JDK 9 and JEP 254, String's private field has type byte[], and each character uses either 1 byte if it's encodable in ISO 8859-1 or 2 bytes if it requires UTF-16. This means that strings containing only ASCII characters can be up to about 2 billion in length, whereas strings with real Unicode content can only be up to about 1 billion in length. This is a bit of an unfortunate regression in functionality.