Exercise Solutions: Inheritance

Line numbers are for reference. They may not match your code exactly.

Class Design

Quick design plan of 1 parent class and 2 child classes

This is one example of how 1 base class (Computer) and 2 derived classes (Laptop & Smartphone) can use inheritance.

  1. Using the diagram above, set up the base class: Computer.
  • Testing the Computer class.
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   public class Computer
   {
      public double Ram { get; set; }
      public double Storage { get; set; }
      public readonly bool hasKeyboard;

      public Computer(double ram, double storage, bool hasKeyboard)
      {
         Ram = ram;
         Storage = storage;
         this.hasKeyboard = hasKeyboard;
      }

      public double IncreaseRam(double extraRam)
      {
         return Ram += extraRam;
      }

      public double IncreaseStorage(double extraStorage)
      {
      return Storage += extraStorage;
      }
   }
  • Use inheritance to create the Laptop derived class.
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   public class Laptop : Computer
   {
      public double Weight { get; set; }

      public Laptop(double ram, double storage, bool hasKeyboard, double weight) : base(ram, storage, hasKeyboard)
      {
      Weight = weight;
      }

      public bool IsClunky()
      {
         if (Weight > 5.0)
         {
            return true;
         }
            else
         {
            return false;
         }
      }
   }

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Class Implementation

  1. Add a new MSTest project to your solution.
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   // one Computer class tests in the Computer Class
   [TestMethod]
   public void TestIncreasingRam()
   {
      Computer testingComputer = new Computer(2, 3, true);
      Assert.AreEqual(2, testingComputer.Ram);
      testingComputer.IncreaseRam(3);
      Assert.AreEqual(5, testingComputer.Ram);
   }
  1. Try to add three MSTest tests to each class. Consider testing each method or field.
  • Testing the Smartphone class
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   //Smartphone Class
   [TestMethod]
   public void TestTakingSelfies()
   {
      SmartPhone testingSmartphone = new SmartPhone(2, 3, true, 800);
      testingSmartphone.TakeSelfie();
      Assert.AreEqual(801, testingSmartphone.NumberOfSelfies);
   }

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Abstract class design

  1. Create the AbstractEntity Class.
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   // AbstractEntity Class
   public class AbstractEntity
   {
      public int Id { get; set; }
      private static int nextId = 1;

      public AbstractEntity()
      {
         Id = nextId;
         nextId++;
      }
   }
  1. Update the Computer class. Remember Computer extends AbstractEntity.
public class Computer : AbstractEntity

Testing AbstractEntity using MSTest:

  1. Testing the Computer Class
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   //Computer Class
   [TestMethod]
   public void TestInheritsId()
   {
      Computer testingComputer = new Computer(2, 3, true);
      Assert.AreEqual(1, testingComputer.Id);

      Computer testingComputer2 = new Computer(4, 6, true);
      Assert.AreEqual(2, testingComputer2.Id);
   }
  1. Testing the Smartphone class
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   //Smartphone class
   [TestMethod]
   public void TestInheritingBaseConstructor()
   {
      SmartPhone testingSmartphone = new SmartPhone(2, 3, true, 800);
      Assert.IsNotNull(testingSmartphone.Id);
      //...
   }

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