Understanding Java String Length Limits and JVM Specification

In this article, the author shares an interview question about whether Java's String has a length limit and, if so, what that limit is, referencing both Java language specifications and JVM compilation rules.

Strings in Java are backed by a char[] array, and the length() method returns an int . Since Java arrays are indexed by integers, the theoretical maximum size of a String is the maximum value of an int (2^31‑1), which corresponds to roughly 4 GB of characters.

However, when a String literal is compiled, it is stored in the class file's constant pool. The constant‑pool entry for a String uses a CONSTANT_Utf8_info structure whose length field is a 2‑byte unsigned value (u2). This limits the literal to 2^16‑1 = 65535 bytes, and because the JVM needs one extra byte for the terminating instruction, the effective compile‑time limit is 65534 characters.

The article includes a small code example showing how to declare arrays in Java:

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

To verify the constant‑pool limit, the author built a String of exactly 65 534 characters using a loop, confirmed its length with an online tool, and successfully compiled it as a literal, demonstrating that the compile‑time limit holds.

In summary, a Java String can hold up to about 2^31‑1 characters at runtime (limited by memory), but a String literal cannot exceed 65 534 characters due to the JVM class‑file constant‑pool specification.