Lab 1 -- Objectdraw Practice

For this first lab, you will write two programs to get to know the Objectdraw library better.

You may help each other with this lab, but the work you turn in must be substantially your own.

Follow these steps to get your BlueJ environment set up for this week's lab assignment.

Your first task is to construct a Java program that draws an image resembling a roadside warning sign, but with a message more appropriate for a computer screen:

First you will need to determine the Java commands required to draw such a picture. Then you will write a Java program that draws and modifies the picture in simple ways in response to mouse events. Implement this program in the NoClicking class you created in your BlueJ project.

A working solution will appear below. Click inside the applet to interact with it.

Specifically, the sign's text should turn red when the mouse enters the window and back to black when the mouse exits. Also, the circle and slash representing the "no" part should disappear when the mouse button is pressed in the window and reappear when the mouse button is released.

Before 11:59 PM, Wednesday, September 18, 2013, submit your Java program for grading. There are three things you need to do to complete the submission: (i) upload a copy of your Java program (the .java file only) using Submission Box under assignment "NoClicking", (ii) print a copy of your program and hand it to your instructor, and (iii) demonstrate the execution of your program for your instructor (2-day grace period for demos).

Your task here is to write a program that counts and displays the number of times the mouse has entered and exited the canvas window, and the number of times a mouse movement has been detected since the last mouse enter event. The latter should be displayed numerically and as a bar.

A working solution for the program should appear below. Click inside the applet to interact with it.

The program draws a 100x100 black square is drawn at (100,100) with white text overlayed to indicate the number of times that the mouse has entered and exited the canvas. There is black text below the square that shows how many times the mouse has moved (as measured by the number of Objectdraw mouse events have been processed) since the last time the mouse entered the canvas. Finally, there is a blue bar (just a FilledRect) whose width changes to show the number of times the mouse has moved.

Implement this program in the EventCounter class you created in your BlueJ project.

This program is not huge, but it is large enough that you should not (and likely could not) type it all in, hit "Compile" and have any chance of it working. Moreover, it will be difficult to figure out what went wrong. For this, and pretty much every program you write this semester (and beyond), you will want to implement and test incrementally. If you add more than one or two new bits of functionality to your program, stop typing, make sure it compiles, and if it does, make sure it does what you expect. This means you are unlikely to introduce more than one or two problems at a time, and you will be more likely to be able to track down problems when you introduce them (they're almost definitely caused by those few lines of code you just added or modified).

For this program, there are a number of orderings of the tasks you need to complete that would work equally well. Here is one possible approach:

Thinking of this in small pieces will feel much less overwhelming than trying to figure out how to do everything at once. Work step by step and don't move on to the next step until you are satisfied that the current step is complete!

Please also do not fall into this very bad habit that is so common among beginning programmers: treating documentation as a final step. Writing comments in your program is not what you do after it all works and before you print it and turn it in. Writing comments before you write the Java code (or at least as you are doing so) is much more effective. If you can't reason and state clearly in English what you want each section of your program to do, how can you hope to do so in Java? By documenting before and/or during the coding process, you will be thinking more clearly about what you are trying to accomplish (thereby being less likely to make mistakes), you will be more likely to remember what the code was supposed to be doing when you go back and look later, and you won't have that annoying last step of going back and trying to add comments so you won't lose points in the grading.

You can set the width and height of a rectangle or oval graphical object by sending it the setWidth and setHeight messages. For example, if you have constructed a FramedRect called myRect and you wish to set its height to 200:

Use constants (private static final CONSTANT_NAME) for all the relevant location and size information. This makes it easier to change the layout and also makes your program much, much easier to read (presuming you give constants good names). Constant names are by convention written with all capital letters and underscores, e.g. THIS_IS_A_CONSTANT.

You may declare Location constants as well by initializing the constant variable with the results of a constructor:

However, you cannot initialize constants whose definition uses canvas (e.g., no FramedRect constants), since Java does not yet know about the canvas when it is initializing the constants.

The widths and heights of wash baskets and the item to be sorted, coordinates of the upper left corner of each of these, etc., are all good candidates for constants.

Note that the constructors for our graphics objects can take a Location object to specify its upper left corner instead of separate numbers for x and y, in cases where that is more convenient, e.g.:

Bottom line, there should rarely be a "magic number" that represents a position or size of an object written in the body of one of your methods. Define named constants for all such numbers at the top of your class.

Before 11:59 PM, Wednesday, September 18, 2013, submit your Java program for grading. There are three things you need to do to complete the submission: (i) upload a copy of your Java program (the .java file only) using Submission Box under assignment "EventCounter", (ii) print a copy of your program and hand it to your instructor, and (iii) demonstrate the execution of your program for your instructor (2-day grace period for demos).

> Feature	Value	Score
No Clicking Sign
Drawing the sign correctly when the program starts	4
Changing the color of the text correctly	4
Making the slash and circle disappear and reappear correctly	4
Event Counter
Initial layout of objects	5
Enter/exit counts updated	5
Color update on exit/enter	3
Update move count number	5
Update move count "bar"	3
Reset count on enter	3
General
Appropriate comments	6
Good variable names	4
Good use of constants	2
Appropriate formatting	2
Total	50