Methods are all well and good as you know them now but they can't do much if they can't communicate with the functions that utilize them. To this end there are two ways that a method can directly communicate with other methods. One is to take in parameters as information to use inside the method and the other is to send back information to the method that called it as a return.
Another valuable piece of information is to consider what variables can be used by different methods in a class. It would be nice to have variables that can be utilized by multiple methods in a class. To do this we can just pass the variable around like described above but we can also create a variable that is global as opposed to the local variables that you have worked with thus far.
For each of the tasks in this lab:
Basic understanding of Java's Math class, how to create methods which return values, and the Turtle commands.
The java.lang.Math class is a set of functions provided by the java structure to allow for more advanced mathematical functions. Some of these functions include power (pow), absolute value (abs), square root (sqrt), etc. For a complete list of functions provided by the Math class see the Sun Java 1.5 API which contains a complete list of the different classes provided by the java framework and what methods they contain. To find Math just scroll in the bottom left hand frame for the Math class and then click it to bring up its specifics. Click here to go directly to the Math class API.
Begin by creating a new project and copying into it you solution to Task 5 from Lab 3 (the "Hour Glass Patrol"). Then modify it as follows.
Make the Random variable global: To make the Random variable global, we need to declare and initialize it outside of all of our methods, but still inside our class. This allows all the methods within the class to use this variable. Hence, we no longer need to pass it when we call methods, so remove those parameters from the method calls and method headings where necessary. Also, we no longer need the variable to be declared in the main method.
Now run your program to verify that it still works as before.
Now we want the size of the hourglass patrol to vary from one patrol to the next. Modify your hourglass method to compute a random distance (i.e. travel time) between 1000 and 4000. Pass this value to each of the triangle methods called by hourglass and use this travel time in those method's forward commands. Verify that your program is working correctly.
We are now computing random values in a few different places in our program: a random turn time in the main method and a random travel time in our hourglass method. Rather than duplicate this code over and over, create a function method called randRange which is passed two ints, the lower end of the range and the higher end of the range, and which returns a random integer in that range.
Now modify your program so that the main method and the hourglass method call the randRange method to compute their need values. Run your program on the Turtle robot to ensure that everything still works as before.
Now let's incorporate some more function
methods and employ some of the builtin methods of the java.lang.Math class.
Create a new copy of Task Three and call it Task Four. Now modify
the code to go in a pattern that takes the Turtle straight out
a random distance from its random turn, turn 90°, go half
the distance it went out forward, turn back towards base and go
the proper distance back to the base. Have the hourglass method
compute this random distance and pass it to the triangle methods
(a different distance for each). The Turtle's path won't look
much like an hourglass anymore.
In your solution, define another function method which is passed the lengths of the two sides of a right triangle and computes the length of the hypotenuse. Call it hypoLength. This method should be called by your triangle methods.
The |
Hopefully you have seen and remember the Pythagorean Theorem, which states that the length of the hypotenuse is the square root of the sum of the squares of the lengths of the sides! |
Lastly something a little more complicated.
You are to redesign Task Four into Task Five, which has both sides
of the right triangle be random distances. To do this you will
need to compute the return angle, which is labeled a in the diagram
to the right. In your solution define a function method returnAngle which
is passed the lengths of the two sides and return the angle the
Turtle needs to turn to return home. Call this method from your
triangle methods.
A |
In your Trigonometry or Precalulus class you no doubt studied the trigonometric functions such as sine, cosine, and tangent. One such function that comes in handy in robotics is arctangent, which can be used to compute the value of the angle a in the diagram above. a is equal to the arctangent of x divided by y (x / y). In Java's Math class this function is called Math.atan(). However, It is important to consider the case when y is 0 (x / 0). This is illegal because as we all know, we cannot divide by 0. But, in looking at the picture above, if y is 0, then the return angle would be 180°. Note that the atan method returns a value which is assumed to be in radians. In order for this code to work easily with our calibrated turtle, we would like this to be in degrees. The math class provides us with a simple method, Math.toDegrees(), which receives in a double (radians) and returns a double (degrees). You will of course have to cast this returned double as an int. |
Write any other methods that you think may simplify your code, such as methods that work with the mathematical computations in Tasks 4 and 5.
In this lab, you learned the following:
