Why Does Java Limit String Literals to 65,534 Characters?

Introduction

In Java, a String is stored in a char[] array, so its length is bounded by the array size and the return type of String.length(), which is int. Since int ranges up to 2³¹‑1, the theoretical maximum number of characters is about 2 147 483 647 (≈4 GB).

Array Length Limit

Arrays in Java are indexed by int, and the maximum array length is therefore 2³¹‑1. This limit applies to the internal char[] used by String.

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

JVM Constant‑Pool Restriction

When a string literal is compiled, the JVM stores it in the class file’s constant pool as a CONSTANT_String entry. The constant‑pool index is a u2 (unsigned 2‑byte) value, which can represent at most 65 535 entries. One byte is needed for the terminating instruction, so the effective maximum length of a string literal is 65 534 characters.

Practical Experiment

A small program builds a string of length 65 534 using a loop, prints its length, and then assigns it as a literal. The compilation succeeds, confirming the constant‑pool limit.

In the class file format, the u2 index can represent values 0‑65535. Because the JVM needs one byte for the terminating instruction, the effective usable range for a string literal is 0‑65534. This limit applies at compile time; at runtime, strings built dynamically can be as long as the int limit allows.

Conclusion

While a Java String can theoretically hold up to about 2 147 483 647 characters, the JVM imposes a compile‑time limit of 65 534 characters for string literals due to the constant‑pool u2 index size. Runtime‑generated strings are only limited by the int array size.