ch03-3Obj

# ch03-3Obj - UsingObjects Ch.3.3 (C),2007.Theymaynotbe...

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1 Building Java Programs Using Objects Ch. 3.3 These lecture notes are copyright (C) Marty Stepp and Stuart Reges, 2007.  They may not be  rehosted, sold, or modified without expressed permission from the authors.  All rights reserved.

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2 Point objects suggested reading: 3.3
3 Point objects Java has a class of objects named  Point . To use  Point , you must write:   import java.awt.*; Constructing a  Point  object, general syntax: Point   <name> = new Point( <x> , <y> ); Point   <name> = new Point(); // the origin, (0, 0) Examples: Point p1 = new Point(5, -2); Point p2 = new Point(); Point  objects are useful for several reasons: They store two values, an (x, y) pair, in a single variable. They have useful methods we can call in our programs.

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4 Point object methods Data stored in each  Point  object: Useful methods of each  Point  object: Point  objects can also be printed using  println  statements: Point p = new Point(5, -2); System.out.println(p); // java.awt.Point[x=5,y=-2] Method name Description distance( p ) how far away the point is from point  p setLocation( x , y ) sets the point's x and y to the given values translate( dx , dy ) adjusts the point's x and y by the given amounts Field name Description x the point's x-coordinate y the point's y-coordinate
5 Using Point objects An example program that uses  Point  objects: import java.awt.*; public class PointMain { public static void main(String[] args) { // construct two Point objects Point p1 = new Point(7, 2); Point p2 = new Point(4, 3); // print each point and their distance apart System.out.println("p1 is " + p1); System.out.println("p2: (" + p2.x + ", " + p2.y + ")"); System.out.println("distance = " + p1.distance(p2)); // translate the point to a new location p2.translate(1, 7); System.out.println("p2: (" + p2.x + ", " + p2.y + ")"); System.out.println("distance = " + p1.distance(p2)); } }

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6 Point objects question Write a program that computes a right triangle's perimeter. The perimeter is the sum of the triangle's side lengths
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ch03-3Obj - UsingObjects Ch.3.3 (C),2007.Theymaynotbe...

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