Programming in Java

Supervision 1

Foreword If you comment your code, so will I!

If any of the following is unclear, please let me know.

Functional translation

Here are 2 very simple programs, written in a pseudo-code for a functional language. N.B. [a] means a list of type a

func :: [Int] -> Int

func [] = 1

func (h:t) = h * func t

func1 :: [Int] -> Int

func1 [] = 0

func1 (h:t) = h + func1 t

func2 :: [Int] -> Int

func2 xs = foldl1 max xs

N.B. max – standard binary operator that returns the maximum of two integers

foldl1 (-) [4,3,6] = -5

foldr1 (-) [4,3,6] = 7

What do these programs do?
Translate them into java:

Create the simplest “Hello World” class with a “public static void main…” method, that instantiates a static member of type int[] with 10 random numbers. (Hint: use the Math class)
Add 3 static methods to this class, following a similar structure to the Power class on page 36 of the notes.

i. The first method should be a translation of “func”

ii. The second method should be a translation of “func1”

iii. The third method should be a translation of “func2”

iv. Add to the main method, code that prints to “std out” the return values of func, func1 and func2 when invoked on the array instantiated in part a. above.

Add a fourth static method with signature: “static void funcs(int[] nums)”, that has exactly the same functionality as the consecutive set of 2 calls to “func” and “func1” in the main method. Comment out these calls and replace with a call to the funcs method. Think about it.

Object orientated programming theory

Explain what is meant by “abstraction” in the context of object orientated programming, giving reasons for and examples of its use. (2 or 3 paragraphs)

Explain what is meant by “encapsulation” in the context of object orientated programming, giving reasons for and examples of its use. (2 or 3 paragraphs)

Explain “subsumption” and “casting” within an object orientated context. Give examples. (Don’t spend too long on this) (2 paragraphs)

Implementing a useful class

Here is a program that rotates an acceleration vector from the co-ordinate system of a sensor it was measured by, into a global co-ordinate system. This is done through multiplication using a rotation matrix, also measured by the sensor. It also calculates whether the rotation matrix is singular, just for fun!

public class MatrixTestHarness

{

public static void main (String[] args)

{

double[][] orientations = {{-0.043536, 0.016970, -0.998908},{0.837222, -0.544945, -0.045747},{-0.545127, -0.838300, 0.009518}};

double[] accelerations = {-5.578592, -8.606017, 0.154298};

Matrix rotationSG = new Matrix(orientations); // Rotation matrix for sensor->global co-ord system

Matrix aS = new Matrix(accelerations, 3); // Acceleration column vector (with, therefore, 3 rows) in sensor co-ord system

Matrix aG = rotationSG.times(aS); // Acceleration column vector in global co-ord system

double GaccX = aG.get(0,0);

double GaccY = aG.get(1,0);

double GaccZ = aG.get(2,0);

System.out.println("Acceleration vector in global coordinate system is: (" + GaccX + ", " + GaccY + ", " + GaccZ + ")");

System.out.print("By the way, the orientation matrix is ");

if (!rotationSG.singular()) {System.out.print("not ");}

System.out.println("singular");

}

Write the class Matrix, so that the above program works. The above test harness is provided. Place the two source files MatrixTestHarness.java and Matrix.java in the same directory to compile.

Detective programming

It is often the case when you program, that you want to do something that someone else has already done. It is also often the case that various generous people share various bits of code so that after trawling the internet for a while, you find the .jar file that contains everything you were about to spend a couple of days writing yourself! This has actually happened within the java language to a certain extent.

However, this does mean you have to develop the skills of quickly understanding whether a set of various classes do in fact meet your requirements and then working out how to use them.

Bearing in mind the question above, is it wished to be able to specify an arbitrary number of sensor co-ordinate systems and transform an acceleration vector into the global co-ordinate system using each of them, in order to compare different sensors.

Complete the provided class Processor in order to make the Filter class test program work. You should make use of the Vector, Iterator and Matrix classes.

Inheritance

Following on from the last part of the second question on “Object orientated programming theory”, fill in the code in InheritanceTest.java so that the following output is obtained:

You are not allowed to declare any other variables, but you are allowed to instantiate classes A, B and C. The files are provided.

public class InheritanceTest

{

static A a = new A();

public static void main(String[] args)

{

//Write code here

//Stop writing code here

}

public class A

{

public char c = 'a';

public void say()

{

System.out.println(c);

}

public void whisper()

{

System.out.println('d');

}

public class B extends A

{

public B()

{

c = 'b';

}

public char d = 'c';

public void shout()

{

System.out.println(d);

}

public void whisper()

{

System.out.println('d');

}

public class C extends A

{

public char c = 'c';

public char d = 'b';

public void shout()

{

System.out.println(d);

}

public void whisper()

{

System.out.println('e');

}