Draw a line in a JPanel with button click in Java

Question

I want to draw a line in a JPanel. This is my GUI and I want a line in the JPanel in white.

Answer 1

Is this going to work like an etch-a-sketch? Then you need to track the current position of the point.

   Point current = new Point(0, 0); //for example.

Then when the user clicks the buttons you can simply increment or decrement x and y accordingly.

On left arrow:

   current.setX(current.getX() - INC);

where INC could be a variable that specifies the length of the distance to draw the line. Maybe 5? Always set a second point p1 to the previous location though.

It is always easier to create a class that extends Canvas or JPanel to draw on rather than draweing directly on the JFrame.

e.g.

public class Circuit extends JFrame {
  Point p1, current;

  JPanel drawPanel;

  //your other declarations

  public Circuit(){
         super();
         drawPanel = new DrawPanel();
         p1 = new Point(0, 0);
         current = new Point(0, 0);
         add(drawPanel, BorderLayout.CENTER);
         //your other code
  }

  class DrawingPanel extends JPanel{

        public void paintComponent(Graphics g){
             g.drawLine(p1.getX(), p1.getY(), current.getX(), current.getY());
        }
  }


   //the rest of your code.
}