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Hi: Can someone give some detail explanations about the following code, which is compiled and run fine. the outputs are ME followed by RUN. I also confuse the purpose on "return null" in the code. If I change to another or move it etc, and get a err.
Thanks.

public class N {

public static void main(String [] arg){
me().run();
}
public static N me(){
System.out.println("ME");
return null;
}
public static void run(){
System.out.println("RUN");
}
}//ME, RUN
 
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I read the following (I don�t remember where):
When you have a reference to an object that has a null value and you call a static method or make a reference to a static member of that class, there �s no NullPointerException thrown.
 
Anonymous
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I also get confuse. What is the meaning about the line in comment//, N is a object?
Thank you.

public class N {
public static void main(String [] arg){

me().run();
}
public static N me(){///
System.out.println("ME");
return null;
}
public static void run(){
System.out.println("RUN");
}
}//ME, RUN
 
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Actually Marcela is right. Because me is declared to return a static reference, call to run is resolved at compile time. That means,
me().run()
gets translated ( at compile time ) to
me();
N.run();
Note that the actual return type of me(), which is null, will not affect the subsequent call to run!!.
Hope this helps.
Ajith
 
Ajith Kallambella
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Here is the byte-code dump of the class file. Note the lines in bold face which substantiate the argument the call to run() is resolved using a static reference.
Method void main(java.lang.String[])
0 invokestatic #8 <Method N me()> --> same as N.me();
3 pop
4 invokestatic #11 <Method void run()> --> same as N.run()
7 return

Method N me()
0 getstatic #9 <Field java.io.PrintStream out>
3 ldc #1 <String "ME">
5 invokevirtual #10 <Method void println(java.lang.String)>
8 aconst_null
9 areturn

Method void run()
0 getstatic #9 <Field java.io.PrintStream out>
3 ldc #2 <String "RUN">
5 invokevirtual #10 <Method void println(java.lang.String)>
8 return
The proof is in the pudding
Ajith
[This message has been edited by Ajith Kallambella (edited August 15, 2000).]
 
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Originally posted by Learner:
Hi: Can someone give some detail explanations about the following code, which is compiled and run fine. the outputs are ME followed by RUN. I also confuse the purpose on "return null" in the code. If I change to another or move it etc, and get a err.
Thanks.
public class N {

public static void main(String [] arg){
me().run();
}
public static N me(){
System.out.println("ME");
return null;
}
public static void run(){
System.out.println("RUN");
}
}//ME, RUN



Static Methods don't need an instance of the class to get invoked. So, you can change your code in main() as
me();
run();
It will still produce the same output. Null is a valid Object/Class reference.
HTH,
Savithri
 
Anonymous
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Thanks. all of you. Now I am clear.
 
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