Sierra and Bates - Self Test Chapter 2 Question 5

[Ross Walker]

According to the self-test answers, the following is a legal method declaration:
private native void m1();
I don't see how this could be legal. It ends in a semi-colon instead of curly braces, so it can't be a concrete method, it must be abstract. Since abstract isn't one of the explicit modifiers, the method must be in an interface, not a class. But you can't have private methods in an interface! Furthermore, abtract methods can't be native.
Can someone please help me out here?
Thanks,
Ross.

[preeti khane]

'native' is an access modifiers for methods denoting that the code implementation is done in a language other than Java... So the code implementation of the method is done in say C, C++ etc..
Such methods can be defined as
native <return type> <method name>();
this is a legal method declaration

[Ross Walker]

I know what native means, but I don't see how it can be legal in this context, as I explained above.

[Roger Chung-Wee]

Just think of a native method as a kind of abstract method, but without the baggage that comes with abstract methods.
Now, a question: can you declare a native method static and, if yes, why.

[Kathy Sierra]

Howdy
Yes, this one looks confusing. The body of a method must be a semicolon if the method is abstract OR if the method is native. So the semicolon there makes it *appear* to be abstract, but it is not. It is simply a declared native method, so it must have a semicolon as the body. So it's legal, but it isn't abstract.
cheers,
Kathy

[Roger Chung-Wee]

This is from one of Sun's free practice exams for SCJP 1.4. The answer does not complain about this not being a complete listing, instead it refers to a bug in the code.
Given:
1. public static void main( String[] args ) {
2. class T1 extends java.lang.Thread{}
3. class T2 extends T1{}
4. class T3 implements java.lang.Runnable{}
5.
6. new T1().start();
7. new T2().start();
8. new Thread(new T3()).start();
9. System.out.println( "Executing" );
10. }