How to draw lines in Java

Question

I'm wondering if there's a funciton in Java that can draw a line from the coordinates (x1, x2) to (y1, y2)?

What I want is to do something like this:

drawLine(x1, x2, x3, x4); 

And I want to be able to do it at any time in the code, making several lines appear at once.

I have tried to do this:

public void paint(Graphics g){    g.drawLine(0, 0, 100, 100); } 

But this gives me no control of when the function is used and I can't figure out how to call it several times.

Hope you understand what I mean!

P.S. I want to create a coordinate system with many coordinates.

Answer 1

A very simple example of a swing component to draw lines. It keeps internally a list with the lines that have been added with the method addLine. Each time a new line is added, repaint is invoked to inform the graphical subsytem that a new paint is required.

The class also includes some example of usage.

import java.awt.BorderLayout; import java.awt.Color; import java.awt.Dimension; import java.awt.Graphics; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import java.util.LinkedList;  import javax.swing.JButton; import javax.swing.JComponent; import javax.swing.JFrame; import javax.swing.JPanel;  public class LinesComponent extends JComponent{  private static class Line{     final int x1;      final int y1;     final int x2;     final int y2;        final Color color;      public Line(int x1, int y1, int x2, int y2, Color color) {         this.x1 = x1;         this.y1 = y1;         this.x2 = x2;         this.y2 = y2;         this.color = color;     }                }  private final LinkedList<Line> lines = new LinkedList<Line>();  public void addLine(int x1, int x2, int x3, int x4) {     addLine(x1, x2, x3, x4, Color.black); }  public void addLine(int x1, int x2, int x3, int x4, Color color) {     lines.add(new Line(x1,x2,x3,x4, color));             repaint(); }  public void clearLines() {     lines.clear();     repaint(); }  @Override protected void paintComponent(Graphics g) {     super.paintComponent(g);     for (Line line : lines) {         g.setColor(line.color);         g.drawLine(line.x1, line.y1, line.x2, line.y2);     } }  public static void main(String[] args) {     JFrame testFrame = new JFrame();     testFrame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);     final LinesComponent comp = new LinesComponent();     comp.setPreferredSize(new Dimension(320, 200));     testFrame.getContentPane().add(comp, BorderLayout.CENTER);     JPanel buttonsPanel = new JPanel();     JButton newLineButton = new JButton("New Line");     JButton clearButton = new JButton("Clear");     buttonsPanel.add(newLineButton);     buttonsPanel.add(clearButton);     testFrame.getContentPane().add(buttonsPanel, BorderLayout.SOUTH);     newLineButton.addActionListener(new ActionListener() {          @Override         public void actionPerformed(ActionEvent e) {             int x1 = (int) (Math.random()*320);             int x2 = (int) (Math.random()*320);             int y1 = (int) (Math.random()*200);             int y2 = (int) (Math.random()*200);             Color randomColor = new Color((float)Math.random(), (float)Math.random(), (float)Math.random());             comp.addLine(x1, y1, x2, y2, randomColor);         }     });     clearButton.addActionListener(new ActionListener() {          @Override         public void actionPerformed(ActionEvent e) {             comp.clearLines();         }     });     testFrame.pack();     testFrame.setVisible(true); }  } 

Answer 2

Store the lines in some type of list. When it comes time to paint them, iterate the list and draw each one. Like this:

Screenshot

DrawLines

import java.awt.Color; import java.awt.Dimension; import java.awt.Graphics; import java.awt.geom.Line2D;  import javax.swing.JOptionPane; import javax.swing.JComponent; import javax.swing.SwingUtilities;  import java.util.ArrayList; import java.util.Random;  class DrawLines {      public static void main(String[] args) {          Runnable r = new Runnable() {             public void run() {                 LineComponent lineComponent = new LineComponent(400,400);                 for (int ii=0; ii<30; ii++) {                     lineComponent.addLine();                 }                 JOptionPane.showMessageDialog(null, lineComponent);             }         };         SwingUtilities.invokeLater(r);     } }  class LineComponent extends JComponent {      ArrayList<Line2D.Double> lines;     Random random;      LineComponent(int width, int height) {         super();         setPreferredSize(new Dimension(width,height));         lines = new ArrayList<Line2D.Double>();         random = new Random();     }      public void addLine() {         int width = (int)getPreferredSize().getWidth();         int height = (int)getPreferredSize().getHeight();         Line2D.Double line = new Line2D.Double(             random.nextInt(width),             random.nextInt(height),             random.nextInt(width),             random.nextInt(height)             );         lines.add(line);         repaint();     }      public void paintComponent(Graphics g) {         super.paintComponent(g);         g.setColor(Color.white);         g.fillRect(0, 0, getWidth(), getHeight());         Dimension d = getPreferredSize();         g.setColor(Color.black);         for (Line2D.Double line : lines) {             g.drawLine(                 (int)line.getX1(),                 (int)line.getY1(),                 (int)line.getX2(),                 (int)line.getY2()                 );         }     } }