How to invoke jdb for this simple code

Question

up to now i have been debugging by looking at the code, could someone please tell me how
to invoke jdb for the following example, and how would i look at the local values within x & y
(without having to rely on JOptionPane):
//pg73 ex2.16 The x value input must be larger than the y value
import javax.swing.JOptionPane;
public class ex2_11
public static void main(String args[])
int x =2, y=3;
JOptionPane.showMessageDialog( null,
"a x= " x            "\n " +
"b the value of x+x is " + (x+x) + "\n " +
"c x= " + "\n " +
"d " + (x+y) + "= " + (y+x),
"Results",JOptionPane.PLAIN_MESSAGE);
System.exit(0);

Answer 1

I think I have already answered this question somewhere else, but I will reiterate it here.
If you have compile errors in your source code (i.e. you left the semi-colon off at the end of a statement), a class file will not get generated.
What you have done is the following:
1. created a working java source file
2. compiled that file and generated a class file
3. then changed the working source file and introduced a compiler error (i.e. you left the semi-colon off at the end of a statement)
4. then attempted to compile the file (with javac), but due to the compiler error a new class file did not get generated (therefore the old class file from the previous compile still resides on your machine).
5. Then you ran jdb on the old previously generated class file.
To confirm what I am saying is true. Delete the class file, then try to generate it again after introducing your compiler error. A new class file will not get generated and therefore you won't be able to use jdb (as jdb requires the class files).
Hope this helps (and gets me the duke dollars),
Tim