JPanel在JApplet上运行

Question

I am designing a JApplet, and basically this applet will allow a user to draw a quadratic equation graph and it inserts the ranges of both x-axis and y-axis. But there is much more to do to reach that point.

I am still in the phase of designing the interface.

Here is my code:

import java.awt.Dimension;

import javax.swing.BoxLayout;
import javax.swing.JApplet;
import javax.swing.JButton;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;


public class Applet extends JApplet {
    JPanel p1;
    JPanel p2;
    JPanel p3;

    JScrollPane s1;

    public Applet() {

    p1 = new JPanel();
    p2 = new JPanel();
    p3 = new JPanel();

    s1 = new JScrollPane(p3,s1.VERTICAL_SCROLLBAR_ALWAYS,s1.HORIZONTAL_SCROLLBAR_ALWAYS);
    }

    @Override
    public void init() {
    super.init();

    for(int i=0;i<100;i++)
    {
        p3.add(new JButton("Hello"));
        p3.add(new JLabel("blah"));
        p3.add(new JButton("Sup"));
    }

    p1.setPreferredSize(new Dimension(this.getWidth(), this.getHeight()));
    p2.setPreferredSize(new Dimension(this.getWidth(),(int) (this.getHeight()*0.6667)));

    p3.setLayout(new BoxLayout(p3,BoxLayout.PAGE_AXIS));
    s1.setPreferredSize(new Dimension(this.getWidth(),(int)(this.getHeight()*0.33333)));

    p1.add(p2);
    p1.add(s1);

    this.add(p1);
    }

}

Answer 1

1. to have the x-axis and y-axis controls on top of each other, you should have two panels, one including the labels and text fields for the x-axis in one and those for the y-axis in the other. You would then add those to a panel that is aligned vertically. ( Box.createVerticalBox() , for example)

2. You can make your graph.java an ActionListener of the 'Plot' and 'Refine' buttons. In the actionPerformed method of graph.java, you can initiate a repaint, gathering the ranges from the 'ControlsB' instance.

EDIT: responding to your comments...

'how to add another panel in order for me to place the x-axis above the y-axis'

this can be as simple as (in ControlsB.java):

b = Box.createHorizontalBox();
b.add(new JLabel("Please enter range:  "));

Box b0 = Box.createVerticalBox();//create a vertical box to stack the controls

Box b1 = Box.createHorizontalBox(); // create a horizontal box for the x-axis

b1.add(new JLabel(" x-axis "));
b1.add(new JLabel("from"));
JTextField f1 = new JTextField("-5");
f1.setMaximumSize(new Dimension(100,30));
b1.add(f1);
b1.add(new JLabel(" to "));
JTextField f2 = new JTextField("5");
f2.setMaximumSize(new Dimension(100,30));
b1.add(f2);
b1.add(new JLabel(".   "));

Box b2 = Box.createHorizontalBox(); // create a second horizontal box for the y-axis
b2.add(new JLabel("y-axis "));
b2.add(new JLabel("from"));
JTextField f3 = new JTextField("5");
f3.setMaximumSize(new Dimension(100,30));
b2.add(f3);
b2.add(new JLabel("to"));
JTextField f4 = new JTextField("-5");
f4.setMaximumSize(new Dimension(100,30));
b2.add(f4);

b0.add(b1); // add the x-axis to the vertical box
b0.add(b2); // add the y-axis to the vertical box
b.add(b0);  // add the vertical box to the parent

b.add(new JButton("Plot"));
b.add(new JButton("Refine"));
add(b); //is this necessary?
}

' and how to gather the ranges from the ControlsB instance...'

You should look into ActionListener s in this tutorial to understand how to make the button click events trigger action in a separate class.

Also, two critiques:

1. in your main class, GraphApplet , you are creating a Box before passing it into each of ControlsA and ControlsB 's constructor. In the constructor, you then reassign the Box that you've passed in. I don't think that you need to do that. Either create the correctly aligned box in GraphApplet , pass that in and don't reassign, or don't pass anything in at all.

2. Your ControlsA and ControlsB classes both extend JPanel . Although you go to the trouble of adding your Box containers to each of these at the end of their constructors, you don't ever add those Controls+ objects to any parent container. In your current implementation, i would suggest that extending JPanel is not necessary.

Answer 2

Recommendations:

• As for having one component on top of another, use a layout manager that would facilitate this such as a vertical BoxLayout.
• For having your display respond to a change in numeric data, I recommend that you design your program in a way to make this easy to implement, by using a Model-View-Controller type application design. Pressing a "plot" or "refine" button would trigger the controller which would update the model's data. The view or GUI would listen for model changes and when they occur would re-plot the graph based on the model's latest data.