How to Accurately Retrieve JPanel Width and Height from an External Class?

Retrieving JPanel Width and Height from an External Class

In your application, you encounter an issue where you need to access the width and height of a JPanel from a separate class (Rect). JPanel provides methods to retrieve its dimensions, but they return 0 when called outside the class.

Passing JPanel Instance to Rect Class

One solution is to pass the JPanel instance as a parameter to the move() method in the Rect class. This provides access to the JPanel's dimensions:

public class Rect {
    //... properties

    public void move(JPanel panel) {
        int jpWidth = panel.getWidth();
        int jpHeight = panel.getHeight();

        // rest of the movement logic using jpWidth and jpHeight
    }
}

Passing Dimension Object

Another approach is to obtain the Dimension object of the JPanel and pass it to the move() method:

public void move(Dimension dimension) {
    int jpWidth = dimension.width;
    int jpHeight = dimension.height;

    // rest of the movement logic using jpWidth and jpHeight
}

Inside the GamePanel class, you can calculate the Dimension object in the paint() method:

public class GamePanel extends JPanel implements Runnable {
    
    private Dimension dimension;

    // rest of the class

    public void paint(Graphics g) {
        super.paint(g);

        dimension = new Dimension(getWidth(), getHeight());

        // ...
    }
}

Then, pass the dimension object to the Rect class:

for(Rect rect:rect){
    rect.move(dimension);
}

Considerations

• The first method is more convenient if you need to access JPanel's width and height directly.
• The second method is more flexible as it provides access to the Dimension object, which can be used for calculations or storage.
• For optimal performance, avoid calculating the Dimension object repeatedly. Use a private variable to cache the latest value.

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