Understanding Java String Length Limits and JVM Constant‑Pool Restrictions

Java developers often wonder whether the String class has a length limit; the answer is yes, both at runtime and at compile time, and the limits differ because of how strings are stored.

At runtime a String is backed by a char[] array, and the length() method returns an int . Since an int in Java can hold values up to 2^31‑1, the theoretical maximum number of characters is about 2 147 483 647 (roughly 4 GB of memory).

When a string literal is compiled, the JVM places it in the class file’s constant pool. The constant‑pool entry for a string is a CONSTANT_String that references a CONSTANT_Utf8_info structure whose length field is a 2‑byte unsigned value (u2). A u2 can represent at most 2^16‑1 = 65 535, but one byte is needed for the terminating instruction, so the effective limit for a literal is 65 534 characters.

Example code illustrating array creation:

int[] arr1 = new int[10]; // array of length 10
int[] arr2 = {1,2,3,4,5}; // array length is 5

The article also shows a small experiment: a string of exactly 65 534 characters is built with a loop, printed, and then assigned to a literal; both compile and run successfully, confirming the compile‑time limit.

In summary, Java strings can be up to 2^31‑1 characters when created at runtime, but source‑code literals are constrained to 65 534 characters because of the JVM constant‑pool’s u2 length field.