嗨，我对 java 很陌生，但是我需要在 JApplet 中绘制图表。我已经设法声明了所有变量和类，方程正在工作（当它自己编译时）。但我得到的只是一条海峡！谁能告诉我我做错了什么？！在这个小程序中，将要求用户插入 abcd 的值以及 x 轴的最小值和最大值
这是我的代码.......任何帮助将不胜感激:)
package CubicEquationSolver;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.*;
import javax.swing.event.*;
public class graphApplet extends JApplet implements ActionListener {
private static class g {
public g() {
}
}
int a;
int b;
int c;
int d;
int minimumX;
int maximumX;
int minimumY;
int maximumY;
int xCoOrdinates[];
int yCoOrdinates[];
int y;
// Setting labels
JLabel labelA = new JLabel("Enter value of A");
JLabel labelB = new JLabel("Enter value of B");
JLabel labelC = new JLabel("Enter value of C");
JLabel labelD = new JLabel("Enter value of D");
JLabel labelMinX = new JLabel("Minimum X value");
JLabel labelMaxX = new JLabel("Maximum X value");
JLabel message = new JLabel("Please insert your values");
// Values will be entered here using JTextField
JTextField textA = new JTextField();
JTextField textB = new JTextField();
JTextField textC = new JTextField();
JTextField textD = new JTextField();
JTextField minX = new JTextField();
JTextField maxX = new JTextField();
JTextField ref = new JTextField("Enter value 0-1");
// declaring the layout for layout manager
JPanel north = new JPanel();
JPanel south = new JPanel();
JPanel west = new JPanel();
JPanel east = new JPanel();
JPanel center = new JPanel();
// declaring buttons using JButtons
JButton calculate = new JButton("Calculate");
JButton delete = new JButton("Delete");
JButton refine = new JButton("Refine");
// Calling from equation class
// equation eq = new equation();
private JPanel panel;
private int width = center.getWidth();
private int height = center.getHeight();
@Override
public void init() {
// setDefaultCloseOperation(EXIT_ON_CLOSE);
Container c = this.getContentPane();
this.setSize(900, 480);
this.setVisible(true);
// listener to buttons
calculate.addActionListener(this);
delete.addActionListener(this);
refine.addActionListener(this);
// listeer to user's input
textA.addActionListener(this);
textB.addActionListener(this);
textC.addActionListener(this);
textD.addActionListener(this);
minX.addActionListener(this);
maxX.addActionListener(this);
ref.addActionListener(this);
// assigning colours to panels to be distinguished
north.setBackground(Color.LIGHT_GRAY);
south.setBackground(Color.LIGHT_GRAY);
west.setBackground(Color.YELLOW);
east.setBackground(Color.GREEN);
center.setBackground(Color.GRAY);
// Declaring border
BorderLayout layoutBorder = new BorderLayout();
// setting up the grid (x rows, y clumns, space, space)
GridLayout layoutGrid = new GridLayout(2, 8, 4, 4);
// layout grid
north.setLayout(layoutGrid);
// set labels
north.add(labelA);
north.add(labelB);
north.add(labelC);
north.add(labelD);
north.add(labelMinX);
north.add(labelMaxX);
north.add(ref);
// calculate button
north.add(calculate);
// text boxes
north.add(textA);
north.add(textB);
north.add(textC);
north.add(textD);
north.add(minX);
north.add(maxX);
north.add(refine);
// delete button
north.add(delete);
south.add(message);
// border layout
c.add(north, BorderLayout.NORTH);
c.add(south, BorderLayout.SOUTH);
c.add(center, BorderLayout.CENTER);
// c .add(west, BorderLayout.WEST);
// c .add(east, BorderLayout.EAST);
// panel = new JPanel();
// panel.setPreferredSize(new Dimension(width, height));
// panel.setBackground(Color.GRAY);
// center.add(panel);
}
@Override
public void actionPerformed(ActionEvent e) // throws NumberFormatException
{
// dafault message will be <message> -- "Please insert values"
message.setText(e.getActionCommand());
// when button "Delete" is pressed all values in text firlds will turn
// null
if (e.getActionCommand().equals("Delete")) {
message.setForeground(Color.DARK_GRAY);
textA.setText(null);
textB.setText(null);
textC.setText(null);
textD.setText(null);
minX.setText(null);
maxX.setText(null);
repaint();
} else if (e.getActionCommand().equals("Calculate"))
// when "Calculate" button is pressed, values will be attached to
// equation
try {
message.setForeground(Color.DARK_GRAY);
// -------------------------------------------------
a = Integer.parseInt(textA.getText());
b = Integer.parseInt(textB.getText());
c = Integer.parseInt(textC.getText());
d = Integer.parseInt(textD.getText());
minimumX = Integer.parseInt(minX.getText());
maximumX = Integer.parseInt(maxX.getText());
System.out.println("center.getWidth() " + center.getWidth());
System.out.println("center.getHeight() " + center.getHeight());
System.out.println("minimum " + minX.getText());
System.out.println("maximum " + maxX.getText());
System.out.println("a " + textA.getText());
System.out.println("b " + textB.getText());
System.out.println("c " + textC.getText());
System.out.println("d " + textD.getText());
// ------------------------------------------------------
message.setText("This is the result for " + "A "
+ textA.getText() + ", B " + textB.getText() + ", C "
+ textC.getText() + ", D " + textD.getText());
draw();
}
catch (NumberFormatException ex)
// if user inputs other than numbers, a warning message in the south
// panel will show
{
message.setText("Please insert numerical value in "
+ ex.getMessage());
message.setForeground(Color.red);
message.setFont(new Font("Tahoma", Font.BOLD, 12));
}
else if (e.getActionCommand().equals("Refine")) {
// for refine
}
}
// ===================================================================================
private void calculation() {
xCoOrdinates = new int[(maximumX - minimumX) + 1];
yCoOrdinates = new int[(maximumX - minimumX) + 1];
for (int i = 0; i < xCoOrdinates.length; i++)
// for(int j = 0; j < yCoOrdinates.length; j++)
{
// generating the x co-ordinates and storing them in arrays
xCoOrdinates[i] = minimumX + i;
// generating the y co-ordinates using the formula given
y = ((a * (int) Math.pow(i, 3)) + (b * (int) Math.pow(i, 2))
+ (c * i) + (d));
// storing y co-ordinates
yCoOrdinates[i] = y;
// displaying results
// System.out.println("X = " + i + " Y = " + getY());
System.out.println("These are the values of X = " + i);
}
// printing the y axes values
for (int i = 0; i < yCoOrdinates.length; i++) {
System.out.println("this is the extracted Y " + yCoOrdinates[i]);
}
maximumX = xCoOrdinates[0];
maximumX = xCoOrdinates[0];
for (int i = 1; i < yCoOrdinates.length; i++) {
if (yCoOrdinates[i] > maximumX)
maximumX = xCoOrdinates[i];
else if (yCoOrdinates[i] < minimumX)
minimumX = xCoOrdinates[i];
}
System.out.println("MAXX is " + maximumX);
System.out.println("MINX is " + minimumX);
maximumY = yCoOrdinates[0];
minimumY = yCoOrdinates[0];
for (int i = 1; i < yCoOrdinates.length; i++) {
if (yCoOrdinates[i] > maximumY)
maximumY = yCoOrdinates[i];
else if (yCoOrdinates[i] < minimumY)
minimumY = yCoOrdinates[i];
}
System.out.println("MAXY is " + maximumY);
System.out.println("MINY is " + minimumY);
}
// =================================================================================================
public void draw() {
Graphics g = center.getGraphics();
g.setColor(Color.GRAY);
g.fillRect(0, 0, center.getWidth(), center.getHeight());
// g.fillRect(25,25, center.getWidth()-50, center.getHeight()-50);
double x, y, nextX, nextY;
int xPoint; // = 0;
int yPoint; // = 0;
int nextXpoint; // = 0;
int nextYpoint; // = 0;
g.setColor(Color.BLUE);
for (xPoint = 0; xPoint <= (double) center.getWidth(); xPoint++) {
x = scaleX(xPoint);
y = equation(x);
yPoint = scaleY(y);
nextXpoint = xPoint + 1;
nextX = scaleX(nextXpoint);
nextY = equation(nextX);
nextYpoint = scaleY(nextY);
g.drawLine(xPoint, yPoint, nextXpoint, nextYpoint);
// System.out.println("equation --->" + eq.getY());
}
}
private double equation(double x) {
return y;
// return a*x*x*x + b*x*x + c*x + d;
}
private double scaleX(int xPoint) {
int minXstart = minimumX;
int maxXend = maximumX;
double xScale = (double) center.getWidth() / (maxXend - minXstart);
return (xPoint - (center.getWidth() / 2)) / xScale;
}
private int scaleY(double y) {
int minYstart = minimumY;
int maxYend = maximumY;
int yCoord;
double yScale = (double) center.getHeight() / (maxYend - minYstart);
yCoord = (int) (-y * yScale) + (int) (center.getHeight() / 2);
return yCoord;
}
}