Question

I have a created a class that inherits from the Manager class that will act as a holder for four other abstract classes called AbstractColumn.

Imagine a table with 4 columns, the table itself is the main class, and each column is AbstractColumn.

I don’t understand why I would get this error.

Here are my classes.

The Main ColumnHolder.java class

package tec.expenses;
import net.rim.device.api.system.Bitmap;
import net.rim.device.api.ui.Manager;
import net.rim.device.api.ui.component.BitmapField;
import net.rim.device.api.ui.component.LabelField;
import net.rim.device.api.ui.container.VerticalFieldManager;
import net.rim.device.api.ui.decor.Background;
import net.rim.device.api.ui.decor.BackgroundFactory;




public class ColumnHolderManager extends Manager{

    private AbstractColumn Entry;
    private AbstractColumn Category;
    private AbstractColumn Date;
    private AbstractColumn Amount;

    protected ColumnHolderManager(long style){
        super(style);

        Background mainBackground = BackgroundFactory.createSolidBackground(0xEEEEEE);
        setBackground(mainBackground);

        AbstractColumn Entry = new AbstractColumn("Entry", NO_HORIZONTAL_SCROLL);
        AbstractColumn Category = new AbstractColumn("Category", NO_HORIZONTAL_SCROLL);
        AbstractColumn Date = new AbstractColumn("Date", NO_HORIZONTAL_SCROLL);
        AbstractColumn Amount = new AbstractColumn("Amount", NO_HORIZONTAL_SCROLL);

        add(Entry);
        add(Category);
        add(Date);
        add(Amount);        
    }

    protected void sublayout(int width, int height) {

        /*layoutChild(this.Entry, 85, 50);
        setPositionChild(this.Entry, 10, 10 );

        layoutChild(this.Category, 85, 50);
        setPositionChild(this.Category, 40, 0 );

        layoutChild(this.Date, 85, 50);
        setPositionChild(this.Date, 70, 0 );

        layoutChild(this.Amount, 85, 50);
        setPositionChild(this.Amount, 100, 0 );*/

        setExtent(360, 203);
    }

}

The abstract AbstractColumn class

package tec.expenses;
import net.rim.device.api.system.Bitmap;
import net.rim.device.api.ui.Manager;
import net.rim.device.api.ui.component.BitmapField;
import net.rim.device.api.ui.component.LabelField;
import net.rim.device.api.ui.decor.Background;
import net.rim.device.api.ui.decor.BackgroundFactory;


public class AbstractColumn extends Manager {
    LabelField labelHeader;

    protected AbstractColumn(String header, long style){
        super(style);

        Background mainBackground = BackgroundFactory.createSolidBackground(0xCACACA);
        setBackground(mainBackground);

        this.labelHeader = new LabelField(header);

        add(labelHeader);       
    }

    protected void sublayout(int width, int height) {

        layoutChild(labelHeader, 80, 30);
        setPositionChild(labelHeader, 5, 5);        

        setExtent(90, 50);
    }
}

As you can see the classes are very simple yet I cannot understand why I would get this error.

I’m making this application for Blackberry using Eclipse as the IDE.

When I comment out the Sublayout methods’ setPositionChild methods I no longer get the exception which means that in the constructor of the ColumnHolderManager class, creating the new AbstractColumn objects aren’t really getting created.

Any help?

Answer 1

In these lines:

AbstractColumn Entry = new AbstractColumn("Entry", NO_HORIZONTAL_SCROLL);
AbstractColumn Category = new AbstractColumn("Category", NO_HORIZONTAL_SCROLL);
AbstractColumn Date = new AbstractColumn("Date", NO_HORIZONTAL_SCROLL);
AbstractColumn Amount = new AbstractColumn("Amount", NO_HORIZONTAL_SCROLL);

you are creating and initializing local variables.

You want to be initializing your instance members. Like this:

Entry = new AbstractColumn("Entry", NO_HORIZONTAL_SCROLL);
Category = new AbstractColumn("Category", NO_HORIZONTAL_SCROLL);
Date = new AbstractColumn("Date", NO_HORIZONTAL_SCROLL);
Amount = new AbstractColumn("Amount", NO_HORIZONTAL_SCROLL);

Also, normal Java code style rules indicate that your members should start with a lower case letter: entry, category, date, amount.