Java重载构造函数和方法

Question

My homework involves a writing a GUI. I am not looking for someone to do my homework for me, but I am only trying to help get a better understanding for it. We are going to code the following classes: Since we need separate classes and separate driver programs to test the classes, I am going to divide up the work. Use the MATH class as needed. Be sure to use the float or double primitive data type as well. Additional students are to have a default constructor (set the default values to 2.0f or 2.0 for a double), as well as overloaded methods to accept the data s either floats or doubles.

Additionally, students are to use Graphical User Interface programming techniques as the interface to the classes. Students can use labels, buttons, radio buttons, menus as well as sliders.

Square Class (Perimeter and Area)

Mainly what I need help with:

Where should the constructors go? How would I implement them to be overloaded in this code? How could I overload methods in this code?

    import javax.swing.*;
    import java.awt.event.*; // Needed for ActionListener Interface

    /**
     * The BugayTestSquare 3 class displays a JFrame that lets the user enter in the
     * sides of the of a square. When the calculate button is pressed, a dialog box
     * will be displayed with the area and perimeter shown. 
     */

    public class FirstGUI extends JFrame
    {
        /*
         * Acording to good class design princples, the fields are private.
         */
        private JPanel panel;
        private JLabel messageLabel, messageLabel2;
        private JTextField lengthTextField;
        private JButton calcButton;
        private final int WINDOW_WIDTH = 310;
        private final int WINDOW_HEIGHT = 150;

        /**
         * Constructor
     */

    public FirstGUI()
    {
        // Set the window title
        setTitle("Area and Perimiter Calculator");

        // Set the size of the window.
        setSize(WINDOW_WIDTH, WINDOW_HEIGHT);

        // Specify what happens when the close button is clicked.
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        // Build the panel and add it to the frame.
        buildPanel();

        // Add the panel to the frames content pane.
        add(panel);

        //diplay the window.
        setVisible(true);
    }

    /** The buildPanel method adds a label, 
     * text field, and a button to a panel.
     **/

    private void buildPanel()
    {
        // Create a label to display instructions.
        messageLabel = new JLabel("Please enter in the length " +
                                  "of the square.");

        messageLabel2 = new JLabel("Please enter in the width " +
                                 "of the square.");

        // Create a text field 10 characters wide.
        lengthTextField = new JTextField(10);

        //Create a button with the caption "Calculate."
        calcButton = new JButton("Calculate");

        // Add an action listener to the button.

        calcButton.addActionListener(new FirstGUI.CalcButtonListener());

        //Create a JPanel object and let the
        // panel field reference it.
        panel =new JPanel();

        // Add the label, text field, and button.
        // components to the panel.

        panel.add(messageLabel);
        panel.add(messageLabel2);
        panel.add(lengthTextField);
        panel.add(calcButton);
    }

    /**
     * CalcButtonListener is an action listener 
     * class for the Calculate button.
     */

    private class CalcButtonListener implements ActionListener
    {
        /**
         * The actionPerformed method executes when the user
         * clicks on the Calculate Button.
         * @param e The Event Object.
         */

        public void actionPerformed(ActionEvent e)
        {
            String input; // To hold the user's input
            double area; // The area
            double perimeter; // the perimter

            // Get the text entered by the user into the
            // text field

            input = lengthTextField.getText();

            //Perform Calculations
            area = Double.parseDouble(input)*2; 
            perimeter = Double.parseDouble(input)*4;

            //Display the result.

            JOptionPane.showMessageDialog(null, "Your area is " +area +
                "\nYour perimter is " + perimeter);

        }
    }
}

Answer 1

This should help:

public class FirstGUI extends JFrame
    {

    public FirstGUI {

        // Constructers go here

     }

}

As for overloading. Picture it like this, you have a debit card, it can be used as a debit card, or a credit card. It has two uses. You can create two methods with the same name, but have different meanings.

Example:

public void functionOne(int num1, int num1) {

// do some stuff

}

public void functionOne(int num1, int num1, String str) {

// do some stuff but has different input

}

public void functionOne(int num1) {

// do some stuff but has different input

}

You can make a call to the method as either:

functionOne(1, 2);

functionOne(1, 2, "hello world");

public void functionOne(59);

And all of the calls will be to a method that has the same name, but with different input. All calls would be correct. You can now call functionOne overloaded.