Adding a class instance of different swing components to a JPanel

Question

I am trying to create a grid of different items that are displayed on a JPanel as shown here:

        JPanel secondPanel = new JPanel();

        secondPanel.setBounds(345,40,640,700);
        secondPanel.setBackground(new java.awt.Color(90,90,100));
        // Here secondPanel is given a gridlayout.  So the items appear in a gridded look.
        secondPanel.setLayout(new GridLayout(3,3,50,50));
        frame.add(secondPanel);

// The following are used as an example of different JPanels.  I am using this to give a demonstration of how the item layout would sort of look like.

        secondPanel.add(new JPanel());
        secondPanel.add(new JPanel());
        secondPanel.add(new JPanel());
        secondPanel.add(new JPanel());
        secondPanel.add(new JPanel());
        secondPanel.add(new JPanel());
        secondPanel.add(new JPanel());
        secondPanel.add(new JPanel());
        secondPanel.add(new JPanel());

Each item has the same properties, however. They all have a select box. They all have a JPanel, they all have a piece of text etc. I thought it would be easier to just create a class that has all these values, and then add those to the JPanel, each one being a separate instance.

Class:

import javax.swing.JPanel;
import javax.swing.JCheckBox;
import javax.swing.JLabel;

public class itemClass {

    itemClass(String name, double cost){

        JPanel box = new JPanel();
        JLabel nameLabel = new JLabel();
        nameLabel.setText(name);
        JCheckBox selectBox = new JCheckBox("$ "+cost);
        box.setForeground(new java.awt.Color(80,80,90));
        box.setSize(50, 50);
        box.add(selectBox);

    }
}

And here I try and create class instances and add them to that panel using the add method:

for (int i = 0; i < 9; i ++) {
            secondPanel.add(new itemClass("T-Shirt",20));
        }

The problem here is that the add method doesn't take in instances of the itemClass . So, I'm looking for a way I can have a class of different swing components and then add them to the secondPanel panel.

Answer 1

You could write it something like this:

import javax.swing.JPanel;
import javax.swing.JCheckBox;
import javax.swing.JLabel;

public class ItemPanel extends JPanel {

    ItemPanel(String name, double cost){
        JLabel nameLabel = new JLabel();
        nameLabel.setText(name);
        this.add(nameLabel);  // added this!
        JCheckBox selectBox = new JCheckBox("$ " + cost);
        this.setForeground(new java.awt.Color(80, 80, 90));
        this.setSize(50, 50);
        this.add(selectBox);
    }
}

The key thing is that your ItemPanel class needs to extend some class that extends JComponent . Extending JPanel is the obvious choice because in this case you need "panel" behavior.

The other way to do this would be to turn your class + constructor into a simple method that creates a JPanel , populates it, and then returns it.

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Other points:

1. Class names should always start with an uppercase letter. No exceptions.

2. Class names should be chosen carefully:

   • They should be describe (or at least hint at) the purpose of the class; eg ItemPanel is a panel that displays an "item".
   • Adding Class at the end of the name is not idiomatic. You don't call your dog "Fido Dog"... and you don't see names like that in the Java SE libraries ¹ .
   • Indeed, the Class suffix is actually misleading, since it suggests that an instance of (say) ItemClass is a representation of a Java class. (It isn't. It is a representation of a component of a user interface!)

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^{1 - There are one or two exceptions, but that's beside the point.}