Algorithms and OOD (CSC 207 2013F) : Labs

Laboratory: Designing Your Own Classes

Summary: In this laboratory, you will extend your knowledge of numeric values in Java.

Primary Classes Used:

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Read through the code to make sure that you understand what it does.

Exercise 1: Multiplication

a. Extend the Fraction class so that it permits multiplication of two fractions.

b. Test your code.

Exercise 2: Fractional Portions

As you may know, we can represent every non-negative rational number as a whole number plus a fractional value no smaller than 0 and strictly less than 1.

a. Write a method of the Fraction class, fractional, that identifies and returns this fractional value as a Fraction. Your procedure need only work for positive numbers. Here are some tests that illustrate what it's supposed to do.

public static void testFractional() {
    Fraction f = new Fraction(11,3);
    assertEquals("2/3", f.fractional().toString());

    f = new Fraction(1,2);
    assertEquals("1/2",  f.fractional().toString());

    f = new Fraction(4,2);
    assertEquals("0", f.fractional().toString());
} // testFractional()

b. Test your procedure and correct any errors.

Exercise 3: From String to Fraction

Write and test a third constructor for the Fraction class. This constructor should accept a string as a parameter, “parse” that string, and generate the appropriate fraction. For example,

public static void stringConstructorTest() {
  Fraction f = new Fraction("1/4");
  assertEquals(1, f.numerator());
  assertEquals(4, f.denominator());
  f = new Fraction("11/5");
  assertEquals(11, f.numerator());
  assertEquals(4, f.denominator());
  f = new Fraction("120/3");
  assertEquals(40.0, f.toReal(), 0.0001);
} // stringConstructorTest()

You can expect that the string will have two positive integers separated by a slash. You may find it useful to reflect on the indexOf method of the java.lang.String class and on various static methods of the java.lang.Integer class.

Exercise 4: A Counter Class

Write and test a class, Counter, that generates objects that can count. Objects in class Counter should provide two methods: increment, which adds 1 to the counter, and get, which gets the current value of the counter.

Make sure to verify that if you create two separate objects in class Counter, you can change the two objects separately.

Exercise 5: Enhancing Counters

a. Update your Counter class to include a second constructor that Allows the user to specify a starting value.

b. Update your Counter class to include a reset method that reset the counter to the starting value.

c. Test both updates to ensure that they work as appropriate.

For Those With Extra Time

Extra 1: Further Enhancing Counters

Identify other methods that would be useful to include in the Counter class and add them.

Extra 2: Further Enhancing Fractions

Identify other methods that would be useful to include in the Fraction class and add them.

Copyright (c) 2013 Samuel A. Rebelsky.

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