Is a Java int always 32 bits?

Yes, it’s defined in The Java Language Specification.

From Section 4.2: Primitive Types and Values:

The integral types are byte, short,
int, and long, whose values are 8-bit,
16-bit, 32-bit and 64-bit signed
two’s-complement integers,
respectively, and char, whose values
are 16-bit unsigned integers
representing UTF-16 code units (§3.1).

And additionally from Section 4.2.1: Integral Types and Values:

The values of the integral types are
integers in the following ranges:

• For byte, from -128 to 127, inclusive
• For short, from -32768 to 32767, inclusive
• For int, from -2147483648 to 2147483647, inclusive
• For long, from -9223372036854775808 to 9223372036854775807, inclusive
• For char, from ‘\u0000’ to ‘\uffff’ inclusive, that is, from 0 to 65535