תרגול 9 מחלקות ואובייקטים

Transcription

1 תרגול 9 מחלקות ואובייקטים 1

2 1. Complex Numbers Design class Complex, representing an immutable complex number. Use this class to read two complex numbers from the user, print their sum and product, and test whether sum equals product.

3 Signatures: constructors and accessors Complex(double real) Complex(double real, double imag) double getreal() double getimage() double getmagnitude() double getangle() What will be the object s state? I.e., what are the fields? Straightforward here, but it s our decision.

4 Signatures: Object class methods overrides boolean equals(object other) String tostring() Why does equals get an Object? When does Java call our tostring?

5 Signatures: operators Complex add(complex other) Complex mul(complex other) Implementation of operators is completely up to us. E.g., can implement mul by multiplying magnitudes and adding angles.

6 Static constants We would also like to have some often-used Complex objects as static fields in class Complex: ZERO, ONE, EYE.

7 Implementation // Public constants public final static Complex ZERO = new Complex(0); public final static Complex ONE = new Complex(1); public final static Complex EYE = new Complex(0, 1); // Private constants private final static double TOLERANCE = 1e-7; // Object state (directly accessed only by constructor and simple accessors) private final double real, imag;

8 Implementation public Complex (double real) { this(real, 0); public Complex (double real, double imag) { this.real = real; this.imag = imag; public double getreal() { return real; public double getimag() { return imag; public double getmagnitude() { return Math.hypot(getReal(), getimag()); public double getangle() { return Math.atan2(getImag(), getreal());

9 public boolean equals(object obj) { boolean res = false; // null is never instanceof of a class if (obj instanceof Complex) { Complex other = (Complex) obj; res = Math.abs(getReal() - other.getreal()) < TOLERANCE && Math.abs(getImag() - other.getimag()) < TOLERANCE; return public String tostring() { return String.format("%.3f%+.3fi", getreal(), getimag()); Use Source Override/Implement methods in means produce an error if no such signature in Object

10 Implementation public Complex add(complex other) { return new Complex(getReal() + other.getreal(), getimag() + other.getimag()); public Complex mul(complex other) { double magnitude = getmagnitude() * other.getmagnitude(); double angle = getangle() + other.getangle(); return new Complex(magnitude * Math.cos(angle), magnitude * Math.sin(angle));

11 Usage Complex zero = Complex.ZERO; System.out.println(zero + ", " + Complex.ONE + ", " + Complex.EYE); double r1, i1, r2, i2; System.out.print("Complex number 1: "); r1 = scanner.nextdouble(); i1 = scanner.nextdouble(); System.out.print("Complex number 2: "); r2 = scanner.nextdouble(); i2 = scanner.nextdouble(); Complex c1 = new Complex(r1, i1), c2 = new Complex(r2, i2); Complex sum = c1.add(c2), prod = c1.mul(c2); System.out.println("Sum = " + sum + ", prod = " + prod + ", eq = " + sum.equals(prod));

12 2. Counter Design class Counter, representing a decimal number of arbitrary length. The number should be kept in an array of integers, one digit in each array cell. Create a counter of length 3, and increment it 250 times, printing the number each time. Create another counter of same length, and decrement it until it is equal to the first counter, printing the final result.

13 Signatures Constructor: Counter(int length) - initializes number to 0 Object class methods overrides: boolean equals(object other) String tostring() Operators: void increment() - adds 1 to the number void decrement() - subtracts 1 to the number

14 Implementation // Private constants private final static int BASE = 10; // Object state private final int[] digits; // Constructor public Counter(int length) { digits = new int[length];

15 public boolean equals(object obj) { boolean res = false; // null is never instanceof of a class if (obj instanceof Counter) { Counter other = (Counter) obj; if (digits.length == other.digits.length) { res = true; for (int i=0; res && i < digits.length; i++) if (digits[i]!= other.digits[i]) res = false; return public String tostring() { String buf = ""; for (int i=0; i < digits.length; i++) buf += digits[i]; return buf;

16 Implementation public void increment() { int i; for (i = digits.length-1; i >= 0 && digits[i] == BASE-1; i--) digits[i] = 0; if (i >= 0) digits[i]++; public void decrement() { int i; for (i = digits.length-1; i >= 0 && digits[i] == 0; i--) digits[i] = BASE-1; if (i >= 0) digits[i]--;

17 Usage Counter c1 = new Counter(3); for (int i = 0; i < 250; i++) { c1.increment(); System.out.println("Counter 1: " + c1); Counter c2 = new Counter(3); while (!c2.equals(c1)) { c2.decrement(); System.out.println("Counter 2: " + c2);

18 3. Dynamic Array Design class DynamicArray, representing a growing array. The underlying array has some initial capacity, and logical size 0. Once logical size is over capacity, underlying array doubles in size. Create a dynamic array of capacity 10, and add 100 numbers to it, where each number is previous number + 2. Multiply each number in the array by 3. Print the array using its String conversion method.

19 Signatures Constructor: DynamicArray(int capacity) Accessors: int length() double get(int index) - checks bounds void set(int index, double value) - checks bounds Object method overrides: String tostring() Operators: void add(double value) - increases array logical size by 1

20 Implementation // Object state private double[] array; private int size; // Constructor public DynamicArray(int capacity) { array = new double[capacity]; this.size = 0; // Accessors public int length() { return size;

21 Implementation public double get(int index) { if (index >= 0 && index < size) return array[index]; else { System.out.println("Out of bounds access"); return Double.NaN; public void set(int index, double value) { if (index >= 0 && index < size) array[index] = value; else System.out.println("Out of bounds access");

22 public String tostring() { String buf = "["; for (int i = 0; i < length(); i++) buf += " " + get(i); buf += " ]"; return buf;

23 Implementation public void add(double value) { if (size == array.length) { double[] copy = new double[size * 2]; System.arraycopy(array, 0, copy, 0, size); array = copy; array[size++] = value;

24 Usage DynamicArray arr = new DynamicArray(10); for (int i=0; i < 100; i++) arr.add(i*2); for (int i=0; i < arr.length(); i++) arr.set(i, arr.get(i) * 3); System.out.println(arr);