Java Language Specification, Version Java SE 21 Edition

5.1. Kinds of Conversion

If a variable is at least as big (bit-width) as a value, then no cast is needed to a assign the value to the variable

Smaller types are never automatically converted into bigger ones without an explicit cast

Numeric types can be coerced to boolean

Every reference type can be coerced to boolean

One can cast between references and ints