Question

In java

Write a program that creates a polyline shape dynamically using mouse clicks. Each mouse click adds a new line segment from the previous point. Include a button below the drawing area to clear the current polyline and begin another.

Answer 1

/*
This applet lets the user draw colored polygons.

The user inputs a polygon by clicking a series of points.
Clicking near the starting point i.e. within 2 pixels /
right-clicking/Command-clicking will complete the
polygon, so the user can begin a new one.

Shift-clicking
will clear the screen. Up to 500 points are allowed in a
polygon.
*/

import java.awt.*;
import java.awt.event.*;
import java.applet.*;

public class SimplePolygons extends Applet implements MouseListener {
  
  
/* Variables for implementing polygon input. */

private int[] xCoordin, yCoordin; // Arrays containing the points of
// the polygon. Up to 500 points
// are allowed.
  
private int pointCt; // The number of points that have been input.

private final static Color polygonColor = Color.red;

public void init() {
  
setBackground(Color.white);
addMouseListener(this);
xCoordin = new int[500];
yCoordin = new int[500];
pointCt = 0;
}


public void paint(Graphics gs) {


gs.setColor(Color.black);
gs.drawRect(0, 0, getSize().width - 1, getSize().height - 1);
  
}


private void putLine(int x1, int y1, int x2, int y2) {
Graphics g = getGraphics();
g.drawLine(x1,y1,x2,y2);
g.dispose();
}


private void putPolygon() {
// Draw the polygon described by the arrays xCoordin and yCoordin
// and the integer pointCt. A filled polygon with a black
// outline is drawn. If pointCt is 0 or 1, nothing is drawn.
// If pointCt is 2, only a black line is drawn.
if (pointCt < 2)
return;
Graphics g = getGraphics();
if (pointCt == 2) {
g.drawLine(xCoordin[0], yCoordin[0], xCoordin[1], yCoordin[1]);
}
else {
g.setColor(Color.red);
g.fillPolygon(xCoordin, yCoordin, pointCt);
g.setColor(Color.black);
g.drawPolygon(xCoordin, yCoordin, pointCt);
}
g.dispose();
}

public void mousePressed(MouseEvent evts) {
// Process a user mouse-click.

if (evts.isShiftDown()) {
// Clear the applet. (This only requires a repaint.)
// Also, set pointCt to zero to start a new polygon.
pointCt = 0;
repaint();
}
else if ( pointCt > 0 && (Math.abs(xCoordin[0] - evts.getX()) <= 2)
&& (Math.abs(yCoordin[0] - evts.getY()) <= 2) ) {
// User has clicked near the starting point.
// Draw the polygon and reset pointCt so that the
// user can start a new polygon.
putPolygon();
pointCt = 0;
}
else if (evts.isMetaDown() || pointCt == 500) {
// Draw the polygon and reset pointCt so that the
// user can start a new polygon.
putPolygon();
pointCt = 0;
}
else {
// Add the point where the user clicked to the list of
// points in the polygon, and draw a line between the
// previous point and the current point.
xCoordin[pointCt] = evts.getX();
yCoordin[pointCt] = evts.getY();
pointCt++;
if (pointCt >= 2) {
putLine(xCoordin[pointCt-2], yCoordin[pointCt-2],
xCoordin[pointCt-1], yCoordin[pointCt-1]);
}
}
  
} // end mousePressed()

public void mouseReleased(MouseEvent evt) { }
public void mouseClicked(MouseEvent evt) { }
public void mouseEntered(MouseEvent evt) { }
public void mouseExited(MouseEvent evt) { }

}