Java: Why am I required to initialize a primitive local variable?

Question

public class Foo {
    public static void main(String[] args) {
        float f;
        System.out.println(f);
    }
}

The print statement causes

Answer 1

Class fields (non-final ones anyway) are initialized to default values. Local variables are not.

It's not always necessary to assign a value when a field is declared. Fields that are declared but not initialized will be set to a reasonable default by the compiler.

So a (non-final) field like f in

class C {
  float f;
}

will be initialized to 0f but the local variable f in

void myMethod() {
  float f;
}

will not be.

Local variables are treated differently from fields by the language. Local variables have a well-scoped lifetime, so any use before initialization is probably an error. Fields do not so the default initialization is often convenient.