In Java, nested classes are categorized as either static member classes or inner classes. Inner classes are non-static member classes, local classes, or anonymous classes.

The compiler will report illegal forward reference when it encounters static int x = y;. This is because source code is compiled from the top down, and the compiler hasn’t yet seen y.

Difference between int and Integer The key difference between the Java int and Integer types is that an int simply represents a whole number, while an Integer has additional properties and methods.