This shouldn't be...

Please observe the following code

Code:

---

                        Scanner input=new Scanner(System.in);

                        System.out.println();
                        System.out.println("Welcome to Breadth First Search TSP Solver");
                        System.out.println("==========================================");
                        System.out.println();

                        System.out.println("Please select preferred distance table:");
                        System.out.println("\t (1) Default distance table");
                        System.out.println("\t (2) User defined distance table");

                        int selectTable=input.nextInt();
                        System.out.println();

                        if(selectTable==1){
                                DistanceTable dt = DistanceTable.getDefault();
                        }else if(selectTable==2){
                                DistanceTable dt = DistanceTable.userTable("test.txt");
                        }else{
                                System.out.println("Invalid input. Program terminated.");
                        }

                        System.out.println("Please select preferred output destination:");
                        System.out.println("\t (1) Monitor screen");
                        System.out.println("\t (2) User defined .txt file");
                        System.out.print("Select 1 or 2: ");

                        int selectOutput=input.nextInt();
                        System.out.println();

                        BfsTSPSolver solver = new BfsTSPSolver();

                        TspIO io=new TspIO(selectOutput);
                        io.execute(dt, solver);

---

Observe the last line io.execute(dt, solver);
When i tried to compile it says that line can't find the symbol for dt...

But isn't dt already defined in the middle with selectTable input??

What am i missing here?

Here the scope of the two dt variables is inside the brackets.
So, generally, you cannot code a conditional variable declaration and
then use that variable outside the scope of the condition....

Code:

---

if(selectTable==1){
  DistanceTable dt = DistanceTable.getDefault(); // <-- "exists" only here
}else if(selectTable==2){
  DistanceTable dt = DistanceTable.userTable("test.txt"); // <-- "exists" only here
}else{
  System.out.println("Invalid input. Program terminated.");
}

---

Try this

Code:

---

DistanceTable dt=null;
if(selectTable==1){
  dt = DistanceTable.getDefault();
}else if(selectTable==2){
  dt = DistanceTable.userTable("test.txt");
}else{
  System.out.println("Invalid input. Program terminated.");
}

---

And, just to be style-picky, the if statement should have been coded as a
switch statement with two cases and a default.

Thx sjalle...

1 more thing, would DistanceTable dt; instead of DistanceTable dt=null;

both the same right? since dt would b initialized later ...

Yes, dt will be null so the initialization in the declaration is redundant.
I'm not sure if the declaration DistanceTable dt; gives initialization at compile
time or during load though (and what would I do with that info ?)

It's just an old habit of mine, it makes visual scanning of code easier, for me at least. :)