Why Does Java’s String Have a Length Limit? Uncovering JVM Constraints

Preface

In Java, the String class has a length limit, which many developers encounter during interviews or when storing large data such as Base64‑encoded files.

String

String stores characters in a char[] array, so its length is ultimately bounded by the maximum size of an array.

The length() method returns an int, and the maximum value of an int (2^31‑1) implies a theoretical maximum array size of about 2 GB of characters (≈4 GB of memory).

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

However, the JVM stores literal strings in the constant pool, where the index is a u2 (unsigned 2‑byte) value, limiting the length to 65 535 bytes. Because the JVM also needs one byte for the terminating instruction, the practical compile‑time limit for a literal string is 65 534 characters.

At runtime, strings built dynamically can be as large as the array limit (≈2^31‑1 characters), but literals exceeding 65 534 characters cause a compilation error.

Note: The array index range is 0‑65535, but the JVM requires an extra byte for the end instruction, so the effective compile‑time range is 0‑65534. Runtime concatenated strings are not subject to this limit.

Experiments constructing a 65 534‑character literal confirm that it compiles successfully, while longer literals fail.