问题
I am trying to plot a two variable equation to a Cartesian plane. Here is my problem, on the code below if I comment out one for loop and let another run, the plot of the graph (the negative or positive sides of x) is correct, but if I run both for loops they seem to alter each other and the graph comes out wrong. I've tried every combination of for loops, looping frontward, backward, nothing seems to solve it.
I commented out the where these loops are at the end of the class "public class DrawingComponent extends JComponent" where it says "// This two loops work fine if each one is run independently"
public class GraphingCalc extends JFrame {
private static final int FRAME_WIDTH = 450;
private static final int FRAME_HEIGHT = 400;
private static final double INITIAL_BALANCE = 1000;
private JLabel rateLabel;
private JTextField rateField;
public JButton button ;
private JLabel resultLabel;
private JPanel basePanel;
private JPanel topPanel; // will contain rateLabel, rateField, and buton
private JPanel bottomPanel; // will contain drawingComponent
JComponent drawingComponent;
Rectangle box;
//////////////////////////////
Graph graphObj;
double xCoord;
int yCoord_size;
double xRate;
double[] yCoord;
//////////////////////////////
public GraphingCalc() {
createTextField();
drawingComponent = new DrawingComponent();
box = new Rectangle(100, 100, 20, 30);
graphObj = new Graph();
xCoord = 0;
yCoord_size = 400;
xRate = 0.101;
yCoord = new double[yCoord_size];
createButton();
createPanel();
setSize(FRAME_WIDTH, FRAME_HEIGHT);
}
private void createTextField() {
rateLabel = new JLabel("Equation: ");
final int FIELD_WIDTH = 10;
rateField = new JTextField(FIELD_WIDTH);
}
public void createButton() {
button = new JButton("Plot");
class AddInterestListener implements ActionListener {
public void actionPerformed(ActionEvent event) {
if(event.getSource() == button) {
//System.out.println("Boo");
graphObj.setEq(rateField.getText());
}
else {
}
//yCoord = Arrays.copyOf(graphObj.setY(), 10);
yCoord = graphObj.getY(drawingComponent.getSize().width);
//for(int i=0; i<10; i++)
//System.out.println("yCoord: " + yCoord[i] +"\n");
revalidate();
repaint();
}
}
ActionListener listener = new AddInterestListener();
button.addActionListener(listener);
}
public class DrawingComponent extends JComponent {
public void paintComponent(Graphics g) {
//////////////////////////
// int scale
// multiply coord values by this
// scale
/////////////////////////
Graphics2D g2 = (Graphics2D) g;
g2.setStroke(new BasicStroke(1f));
//g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
int drawArea_width = getSize().width;
int drawArea_height = getSize().height;
/////////////////////
// x axis
g2.draw(new Line2D.Double( 0, drawArea_height/2, drawArea_width ,drawArea_height/2 ));
Font font = new Font("Times New Roman", Font.PLAIN, 10);
g2.setFont(font);
//positive x axis values
for(int i = 1; i < 20; i++) {
String num = Integer.toString(i);
if(i >= 10) {
g2.draw(new Line2D.Double((drawArea_width/2 -19 ) + i*12 , (drawArea_height/2) -2 , (drawArea_width/2 -19 ) + i*12 , (drawArea_height/2) + 2 ));
g2.drawString(num, (drawArea_width/2 -22 ) + i*12 , (drawArea_height/2) + 15 );
}
else {
g2.draw(new Line2D.Double((drawArea_width/2) + i*10 , (drawArea_height/2) -2 , (drawArea_width/2) + i*10 , (drawArea_height/2) + 2 ));
g2.drawString(num, (drawArea_width/2 -1) + i*10 , (drawArea_height/2) + 15 );
}
}
//
//negative x axis values
for(int i = 20; i > 0; i--) {
String num = Integer.toString(i);
if(i <= 9) {
g2.draw(new Line2D.Double((drawArea_width/2 ) - i*13 , (drawArea_height/2) -2 , (drawArea_width/2 ) - i*13 , (drawArea_height/2) + 2 ));
g2.drawString("-" + num, (drawArea_width/2 - 4) - i*15 , (drawArea_height/2) + 15 );
}
else {
g2.draw(new Line2D.Double((drawArea_width/2 + 16 ) - i*15 , (drawArea_height/2) -2 , (drawArea_width/2 + 16 ) - i*15 , (drawArea_height/2) + 2 ));
g2.drawString("-" + num, (drawArea_width/2 + 16 ) - i*17 , (drawArea_height/2) + 15 );
}
}
//
//////////////////////
//y axis
g2.draw(new Line2D.Double( drawArea_width/2, 0, drawArea_width/2, drawArea_height ));
g2.setStroke(new BasicStroke(1.20f));
// This two loops work fine if each one is run independently
xCoord = 0;
for(int i = 0; i < yCoord_size/2 ; i++) {
//g2.draw(new Line2D.Double((drawArea_width/2 ) + xCoord , yCoord[i] + (drawArea_height/2), (drawArea_width/2 ) + xCoord , yCoord[i] + (drawArea_height/2) ) );
g2.draw(new Ellipse2D.Double((drawArea_width/2 ) + xCoord , yCoord[i] + (drawArea_height/2), 1, 1));
xCoord-= xRate;
}
/*
for(int i = yCoord_size/2; i < yCoord_size ; i++) {
//g2.draw(new Line2D.Double((drawArea_width/2 ) + xCoord , yCoord[i] + (drawArea_height/2), (drawArea_width/2 ) + xCoord , yCoord[i] + (drawArea_height/2) ) );
g2.draw(new Ellipse2D.Double((drawArea_width/2 ) + xCoord , yCoord[i] + (drawArea_height/2), 1, 1));
xCoord+= xRate;
}
*/
}
}
private void createPanel() {
basePanel = new JPanel();
topPanel = new JPanel();
basePanel.setLayout(new BorderLayout());
topPanel.add(rateLabel);
topPanel.add(rateField);
topPanel.add(button);
basePanel.add(topPanel, BorderLayout.NORTH);
basePanel.add(drawingComponent, BorderLayout.CENTER);
add(basePanel);
}
}
public class Graph {
int yCoord_size;
double xRate;
String equation;
double[] yCoord;
static double num;
public Graph() {
yCoord_size = 400;
xRate = 0.101;
equation = "";
num = 0;
yCoord = new double[yCoord_size];
for(int i=0; i <10; i++)
yCoord[i] = 0;
}
public void setEq(String eq) {
equation = eq;
//System.out.println("eq is: " + eq);
}
public double equationStrToVal(String eq, double inX){
double total = 0.0;
double x = inX;
String[] tokens;
tokens = eq.split(" ");
for(int i=0; i<tokens.length; i++){
if(tokens[i].equalsIgnoreCase("x")){
total+= x;
}
//addition
else if(tokens[i].equals("+")){
if(tokens[i+1].equalsIgnoreCase("x"))
total+= x;
else
total+= stringToDouble( tokens[i+1]);
i++;
}
//multiplication
else if(tokens[i].equals("*")){
if(tokens[i+1].equalsIgnoreCase("x"))
total*= x;
else
total*=stringToDouble( tokens[i+1]);
i++;
}
//raised to a power
}
return total;
//System.out.println("The result is: " + total);
}
public double[] getY(int screen_width) {
double j = 0.0;
//for(int i=0 ; i < screen_width/2; i++, j-=0.05)
for(int i=0 ; i < yCoord_size/2; i++, j-=xRate)
yCoord[i] = -1 * equationStrToVal(equation, j);
j = 0;
//for(int i=screen_width/2 ; i<screen_width ; i++, j+=0.05)
for(int i= yCoord_size/2 ; i< yCoord_size ; i++, j+=xRate)
yCoord[i] = -1 * equationStrToVal(equation, j);
return yCoord;
}
static double stringToDouble(String num){
return ( Double.valueOf(num.trim()).doubleValue());
}
}
public class GraphingCalcViewer {
public static void main(String[] args) {
JFrame frame = new GraphingCalc();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
}
回答1:
if you comment out one loop the other loop always start with xCoord = 0;
if you run both loops the second starts with the current xCoord.value
it looks like you have to set "xCoord = 0;" before the second loop;
来源：https://stackoverflow.com/questions/10776728/plotting-equation-to-cartesian-plane