While loop doesn't loop in java

Question

My while loop in Java doesn't loop even though the boolean is still false (I think?).

If I remove all the "mysqlStatus = true" it still doesn't want to loop. I don't really understand how that is possible as I never switch the boolean to "true".

It's probably something stupid though so thanks in advance for the help :).

The loop:

    Connection conn;
    Boolean mysqlStatus = false;

    while(mysqlStatus.equals(false)) {

        try {
            Class.forName(driver).newInstance();
            conTest = DriverManager.getConnection(host + dbName, username, password);
            mysqlStatus = true;
        } catch (SQLException e) {
            // server offline

            Alert alert = new Alert(AlertType.CONFIRMATION);
            alert.setTitle("Database offline");
            alert.setHeaderText("De MySQL database server is offline");
            alert.setContentText("Start de server en probeer opnieuw.");

            ButtonType buttonTypeOne = new ButtonType("Opnieuw controleren");
            ButtonType buttonTypeCancel = new ButtonType("Exit", ButtonData.CANCEL_CLOSE);

            alert.getButtonTypes().setAll(buttonTypeOne, buttonTypeCancel);

            Optional<ButtonType> result = alert.showAndWait();
            if (result.get() == buttonTypeOne){
                mysqlStatus = false;
                alert.close();
            } else {
                System.exit(0);
            }
        } catch (Exception e) {
            mysqlStatus = false;
            ExceptionDialog cexD = new ExceptionDialog();
            cexD.setStrError("Er is een onverwachte fout opgetreden.");
            cexD.setException(e);
        } finally {
            try {
                conTest.close();
            } catch (SQLException e) {
                mysqlStatus = false;
                ExceptionDialog cexD = new ExceptionDialog();
                cexD.setStrError("Er is een onverwachte fout opgetreden.");
                cexD.setException(e);
            }
        }

    }

Nabin · Accepted Answer · 2016-03-12 15:49:16Z

3

You don't do

mysqlStatus.equals(false)

in java. Not sure what that will do.

You need to do

(!mysqlStatus)

for checking conditions.

answered Mar 12, 2016 at 15:49

Nabin

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5 Comments

Niell Over a year ago

Changed it and it still doesn't loop.

Yassin Hajaj Over a year ago

@Niell How do you know it does not loop? Do not forget that you put your variable to true within the try clause.

resueman Over a year ago

Did you test that though? It's not normal, but it should still work.

Nabin Over a year ago

That is other problem @Niell

Niell Over a year ago

I removed all the code where I put it to true before I tested it. I'm running this code in a constructor of an object if it matters?

Joop Eggen · Accepted Answer · 2016-03-12 16:00:40Z

0

Any Exception besides an SQLException like ClassNotFoundException will be catched by Exception and loop endlessly. There call break or such.

Boolean is the Object wrapper class for the primitive type boolean.

boolean mysqlStatusVastgesteld = false;

while (!mysqlStatusVastgesteld) {

answered Mar 12, 2016 at 16:00

Joop Eggen

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Comments

Ian · Accepted Answer · 2016-03-12 16:08:05Z

0

From here:

The java.lang.Boolean.equals(Object obj) returns true if and only if the argument is not null and is a Boolean object that represents the same boolean value as this object.

now false is a primitive boolean literal (which is either true or false and not Boolean object. Boolean object can be true, false, or NULL)

So, what happen when you do:

mysqlStatus.equals(false)

is you compare a Boolean object mysqlStatus with boolean primitive literal false (and not Boolean object with false value) and therefore it always returns false (because mysqlStatus is not the same Boolean object as false) and as a result you never enter the while loop.

Do this to compare if mysqlStatus is false with Boolean object:

while(Boolean.FALSE.equals(mysqlStatus)) //also handle NULL

edited Mar 12, 2016 at 16:08

answered Mar 12, 2016 at 15:53

Ian

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Comments

Niell · Accepted Answer · 2016-03-12 16:10:00Z

0

I fixed it by making a function that checks the status.

    public Boolean checkStatus() {

        try {
            Class.forName(driver).newInstance();
            Connection conTest = DriverManager.getConnection(host + dbName, username, password);
            return true;
        } catch (Exception e) {
            // server offline
            return false;
        }

    }

I also made a while loop that runs this function until it returns true. If it returns false a dialog appears and asks to retry or exit.

All works now. This was a weird issue but thanks everyone for trying to help! There were multiple mistakes in my code.

answered Mar 12, 2016 at 16:10

Niell

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