Java - For-loop with two conditions does not work as expected

Question

I have coded two for-loops which should fill a GridBagLayout. Somehow the second condition does not come to operation and therefore I get an exception.

So basically what the program does: It gets the data from a MySQL Server and lists it in a GridBagLayout. Therefore I get the lenght of the row by using rs.lenght and rs.getRow(). Than I copy it to lenghtCounter for the inner for-loop(with the x variable). The inner for-loop should be executed after 3 cycles OR if lenghtCounter is equal to 0. I see in the console that the counter works and gets down to 0 as expected but the for-loop does not break. Instead it continues and gives me an exception.

Here is the code:

        try {
            ResultSet rs = MySQL.getStatement().executeQuery(
                    "select * from obj_house");
            rs.last();
            int lenghtCounter = rs.getRow();
            int lenght = lenghtCounter;
            rs.first();
            System.out.println(lenghtCounter + " " + (lenght / 3));

            for (int y = 0; y <= (lenght / 3); y++) {
                for (int x = 0; x < 3 || lenghtCounter==0; x++) {
                    System.out.println("ID " + lenghtCounter);

                    JButton street = new JButton("Strasse: " + rs.getString(5));

                    gbcOut.gridx = x;
                    gbcOut.gridy = y;
                    panelBottom.add(street, gbcOut);

                    System.out.println("X: " + x);
                    System.out.println("Y: " + y);
                    rs.next();
                    lenghtCounter--;
                    System.out.println("lenght: " + lenghtCounter);
                }
            }
        } catch (SQLException e1) {
            // TODO Auto-generated catch block
            e1.printStackTrace();
        }

can you update your question with the error stacktrace?

Debojit Saikia
– Debojit Saikia

2013-10-29 13:55:43 +00:00
Commented Oct 29, 2013 at 13:55 — Debojit Saikia
– Debojit Saikia, Commented Oct 29, 2013 at 13:55
java.sql.SQLException: After end of result set

THE-E
– THE-E

2013-10-29 14:00:08 +00:00
Commented Oct 29, 2013 at 14:00 — THE-E
– THE-E, Commented Oct 29, 2013 at 14:00

Julien · Accepted Answer · 2013-10-29 13:58:28Z

3

Try with the test :

x < 3 && lenghtCounter>0

answered Oct 29, 2013 at 13:58

Julien

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2 Comments

THE-E Over a year ago

Thanks! :) This works perfect. Now I see the mistake. I thought it is the condition to terminate the operation. But it is the condition to continue the operation. Is that right ? A small explaination would be helpful :)

Julien Over a year ago

You're right : the condition in an if statement should be red as a condition in a while. It continues until the condition becomes false.

Radiodef · Accepted Answer · 2013-10-29 14:10:30Z

2

|| won't work as expected here because the for loop condition works the other way. A for loop condition is the same as a while loop condition. The loop breaks when the condition you specify evaluates as false. So the way you've specified it, the loop will run while either x < 3 || lenghtCounter == 0.

I think what you want is:

x < 3 && lenghtCounter != 0

or:

x < 3 && lenghtCounter > 0.

(Also lenghtCounter a typo?)

answered Oct 29, 2013 at 14:10

Radiodef

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Comments

gvlasov · Accepted Answer · 2013-10-29 13:59:09Z

1

You probably don't need || lenghtCounter==0. When lengthCounter reaches 0 you call rs.next() one extra time, and that's why you're possibly getting the exception.

answered Oct 29, 2013 at 13:59

gvlasov

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Comments

jeubank12 · Accepted Answer · 2013-10-29 13:59:14Z

1

If I had to guess you are trying to not have the inner loop run until the outer loop has run three times. However, each time the outer loop runs, x is reset to 0 due to scope. Recheck your scoping - declare x before the loops.

Additionally, your outer loop will do nothing by itself. You may want to switch to a while loop with multiple logic incrementers for x and y.

answered Oct 29, 2013 at 13:59

jeubank12

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