Java中ByteArrayOutputStream的toByteArray()[]语法在哪有文档说明？

Great question! Let's unpack this syntax you found in ByteArrayOutputStream's source code.

Where is this syntax documented officially? #

This is a valid syntax defined in the Java Language Specification (JLS). Specifically, Section 8.4.7 (Method Return Type) clarifies that when declaring a method returning an array type, you can place the square brackets in two equivalent positions:

• After the element type (the more common, widely recommended style: public synchronized byte[] toByteArray())
• Or after the method identifier (the style you encountered: public synchronized byte toByteArray()[])

All standard Java compilers recognize both forms as syntactically identical.

Is this consistent with regular array declaration rules? #

Absolutely! This is just an extension of the same flexibility you see in variable declarations. For example:

• String[] args; (brackets placed after the type)
• String args[]; (brackets placed after the variable name)

These two declarations mean exactly the same thing—args is a reference to a String array. The method return type syntax follows this exact logic: the brackets can be associated with the element type or the method name, with no difference in functionality.

A quick note on your 2018 observation #

You mentioned discovering more such special syntax uses later—this pattern applies to method parameters too! For example:

public void processData(int data[]) { /* ... */ }

is completely equivalent to:

public void processData(int[] data) { /* ... */ }

While the style with brackets after the type is favored for readability in most codebases, the compiler accepts both forms without distinction.

内容的提问来源于stack exchange，提问作者smac89