Topic: Array of Objects
Name: _____________________________________________________
Lab 07: Connect the Dots
Period: _______ Date: _______________________
w/ MouseListener Interface
Objectives
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

I will implement the MouseListener interface.
I will be able to use the Point object.
I will be able maintain an array of Points.
Point
A Point object represents a point on a coordinate plane. It has 2 variables: x and y,
The Point object has a 2 argument constructor:
Point (int x, int y)
Array of Points
Create an array of 10 Points called points:
Declare and initialize a variable that will indicate where the next Point object will be put into
the array:
int arrayIndex = 0;
Creating a Point and putting it
into the points array
In mousePressed, create a Point object with the coordinates from the mouse:
public void mousePressed (MouseEvent e)
{
int x = e.getX();
int y = e.getY();
Point pt = new Point(x, y);
Put the point into the array, if there is enough space available. If they array is full, print an
error message:
if (arrayIndex < points.length)
{
}
else
System.out.println(“Array is full”);
Connecting the Points
In paintComponent(Graphics g), we want to draw a line between all the points;
Couple things we need to know how to do:
1. How do you traverse the points array and access each Point:
for (int k=0; k<arrayIndex; k++)
{
Point pt1 = points[k];
2. How do you get the x and y values from a Point
int x1 = (int) pt1.getX();
int y1 = (int) pt1.getY();
3. How do you get the rest of the points starting from the current position (index ):
for (int j=k+1; j<arrayIndex; j++)
{
Point pt2 = points[j];
int x2 = (int)pt2.getX();
int y2 = (int)pt2.getY();
4. Draw the line between (x1, y1) and (x2, y2)
Clear the array when we detect
the mouse has exited and reentered the panel.
Reallocating the array when it
fills up.
To clear the array, set the index to 0:
arrayIndex=0;
When the array is full, we can stop adding new Points or we can create a new array that is
larger than the original and copy all the elements.
public Point [] reallocate_Point_array (Point [] a)
{
Point [] b = new Point[a.length*2];
for (int k=0; k<a.length; k++)
b[k] = a[k];
return b;
}
We can then set our reference, points, to the new array:
if (arrayIndex >= points.length)
points = reallocate_Point_array(points);
Changing the color based on
the distance between points.
When we draw a line between 2 points, we can set the color so that it’s correlated to the
distance. In paintComponent( Graphics g ), we’ll set the color to a shade of gray before
calling g.drawLine(….) :
double distance = computeDistance(x1, y1, x2, y2);
int colorVal = (int)(distance * 255 / getWidth());
if (colorVal > 255)
colorVal = 255;
Color cc = new Color(colorVal, colorVal, colorVal);
g.setColor(cc);
g.drawLine(x1, y1, x2, y2);