SL275: Module2: Object-Oriented Programming
Exercise #3: Create a Simple Banking Package
(level 2)
Objective
This exercise will introduce you to the banking project which we will return to in several labs up to Module 9. This project will (eventually) consist of a bank with several customers with several account each and a report. These classes will evolve over the next eight modules. In this exercise, you will create very simple version of the Account class. You will place this source file in the banking package. A test program, TestBanking, has been written in the default package that creates a single account. It initializes the balance of that account and performs several simple transactions. Finally, the test program displays the final balance of the account.
Directions
Start by changing your working directory to SL275/mod02/exercise3 on your computer. Create the banking directory. Use a command such as:
mkdir banking
Create the Account class in the file Account.java under the banking directory. This class must implement the model in the above UML diagram. declare one private object attribute: balance; this attribute will hold the current (or "running") balance of the bank account
declare a public constructor that takes one parameter (init_balance); that populates the balance attribute
declare a public method getBalance that retrieves the current balance
declare a public method deposit that adds the amount parameter to the current balance
declare a public method withdraw that removes the amount parameter from the current balance In the main exercise3 directory, compile the TestBanking.java file. This has a cascading effect of compiling all of the classes used in the program; thus compiling the Customer.java and Account.java files under the banking directory.
javac -d . TestBanking.java Run the TestBanking class. You shoud see the following output:
Creating an account with a 500.00 balance.
Withdraw 150.00
Deposit 22.50
Withdraw 47.62
The account has a balance of 324.88SL275: Module2: Object-Oriented Programming
Exercise #2: Explore Encapsulation
(Level 2)
Objective
In this exercise you will explore the purpose of proper object encapsulation. You will create a class in three steps demonstrating the use of information hiding. Directions
Version 1: No Information HidingIn this version of the Vehicle class, you will leave the attributes public so that the test program TestVehicle1 will have direct access to them. Change your working directory to mod02/exercise2/version1. Create a class Vehicle that implements the above UML diagram. Include two public attributes: load "the current weight of the vehicle's cargo" and maxLoad "the vehicle's maximum cargo weight limit".
Include one public constructor to set the maxLoad attribute.
Include two public access methods: getLoad to retrieve the load attribute and getMaxLoad to retrieve the maxLoad attribute.
Note that all of the data are assumed to be in kilograms.
Read the TestVehicle.java code. Notice that the program gets into trouble when the last box is added to the vehicle's load because the code does not check if adding this box will exceed the maxLoad. Compile the Vehicle and TestVehicle classes. Run the TestVehicle class. The output generated should be:
Creating a vehicle with a 10,000kg maximum load.
Add box #1 (500kg)
Add box #2 (250kg)
Add box #3 (5000kg)
Add box #4 (4000kg)
Add box #5 (300kg)
Vehicle load is 10050.0 kgVersion 2: Basic Information HidingTo solve the problem from the first version, you will hide the internal class data (load and maxLoad) and provide a method, addBox, to perform the proper checking that the vehicle is not being overloaded. Change your working directory to mod02/exercise2/version2. Create a class Vehicle that implements the above UML diagram.
You may wish to copy the Vehicle.java file you created in version #1.
Modify the load and maxLoad attributes to be private.
Add the addBox method. This method takes a single argument, which is the weight of the box in kilograms. The method must verify that adding the box will not violate the maximum load. If a violation occurs the box is rejected by returning the value of false; otherwise the weight of the box is added to the vehicle load and the method returns true.
Hint: you will need to use an "if" statement. Here is the basic form of the conditional form: if ( <boolean_expression> ) {
<statement>*
} else {
<statement>*
}
Note that all of the data are assumed to be in kilograms.
Read the TestVehicle.java code. Notice that the code can not modify the load attribute directly, but now must use the addBox method. This method returns a true or false value which is printed to the screen. Compile the Vehicle and TestVehicle classes. Run the TestVehicle class. The output generated should be:
Creating a vehicle with a 10,000kg maximum load.
Add box #1 (500kg) : true
Add box #2 (250kg) : true
Add box #3 (5000kg) : true
Add box #4 (4000kg) : true
Add box #5 (300kg) : false
Vehicle load is 9750.0 kgVersion 3: Change Internal Representation of Weight to NewtonsNow suppose that you were going to write some calculations that determine the wear on the vehicle's engine and frame. These calculations are easier if the weight of the load is measured in newtons. Change your working directory to mod02/exercise2/version3. Create a class Vehicle that implements the above UML diagram.
You may wish to copy the Vehicle.java file you created in version #2.
Modify the constructor, getLoad, getMaxLoad, and addBox methods to use a conversion from kilograms (the parameter weight measurement) to newtons (the instance variable measurement). You might want to use the following private methods:
private double kiloToNewts(double weight) {
return (weight * 9.8);
}
private double newtsToKilo(double weight) {
return (weight / 9.8);
}Note that now the internal data of the vehicle objects is in newtons and the external data (passed between methods) is still in kilograms.
Read the TestVehicle.java code. Notice that it is identical to the test code in version #2. Compile the Vehicle and TestVehicle classes. Run the TestVehicle class. The output generated should be:
Creating a vehicle with a 10,000kg maximum load.
Add box #1 (500kg) : true
Add box #2 (250kg) : true
Add box #3 (5000kg) : true
Add box #4 (4000kg) : true
Add box #5 (300kg) : false
Vehicle load is 9750.0 kg
You should see no change in the output of the program. This demonstrates that the (private) internal changes to the version #3 Vehicle class did not change the code of the client class TestVehicle.
Exercise #3: Create a Simple Banking Package
(level 2)
Objective
This exercise will introduce you to the banking project which we will return to in several labs up to Module 9. This project will (eventually) consist of a bank with several customers with several account each and a report. These classes will evolve over the next eight modules. In this exercise, you will create very simple version of the Account class. You will place this source file in the banking package. A test program, TestBanking, has been written in the default package that creates a single account. It initializes the balance of that account and performs several simple transactions. Finally, the test program displays the final balance of the account.
Directions
Start by changing your working directory to SL275/mod02/exercise3 on your computer. Create the banking directory. Use a command such as:
mkdir banking
Create the Account class in the file Account.java under the banking directory. This class must implement the model in the above UML diagram. declare one private object attribute: balance; this attribute will hold the current (or "running") balance of the bank account
declare a public constructor that takes one parameter (init_balance); that populates the balance attribute
declare a public method getBalance that retrieves the current balance
declare a public method deposit that adds the amount parameter to the current balance
declare a public method withdraw that removes the amount parameter from the current balance In the main exercise3 directory, compile the TestBanking.java file. This has a cascading effect of compiling all of the classes used in the program; thus compiling the Customer.java and Account.java files under the banking directory.
javac -d . TestBanking.java Run the TestBanking class. You shoud see the following output:
Creating an account with a 500.00 balance.
Withdraw 150.00
Deposit 22.50
Withdraw 47.62
The account has a balance of 324.88SL275: Module2: Object-Oriented Programming
Exercise #2: Explore Encapsulation
(Level 2)
Objective
In this exercise you will explore the purpose of proper object encapsulation. You will create a class in three steps demonstrating the use of information hiding. Directions
Version 1: No Information HidingIn this version of the Vehicle class, you will leave the attributes public so that the test program TestVehicle1 will have direct access to them. Change your working directory to mod02/exercise2/version1. Create a class Vehicle that implements the above UML diagram. Include two public attributes: load "the current weight of the vehicle's cargo" and maxLoad "the vehicle's maximum cargo weight limit".
Include one public constructor to set the maxLoad attribute.
Include two public access methods: getLoad to retrieve the load attribute and getMaxLoad to retrieve the maxLoad attribute.
Note that all of the data are assumed to be in kilograms.
Read the TestVehicle.java code. Notice that the program gets into trouble when the last box is added to the vehicle's load because the code does not check if adding this box will exceed the maxLoad. Compile the Vehicle and TestVehicle classes. Run the TestVehicle class. The output generated should be:
Creating a vehicle with a 10,000kg maximum load.
Add box #1 (500kg)
Add box #2 (250kg)
Add box #3 (5000kg)
Add box #4 (4000kg)
Add box #5 (300kg)
Vehicle load is 10050.0 kgVersion 2: Basic Information HidingTo solve the problem from the first version, you will hide the internal class data (load and maxLoad) and provide a method, addBox, to perform the proper checking that the vehicle is not being overloaded. Change your working directory to mod02/exercise2/version2. Create a class Vehicle that implements the above UML diagram.
You may wish to copy the Vehicle.java file you created in version #1.
Modify the load and maxLoad attributes to be private.
Add the addBox method. This method takes a single argument, which is the weight of the box in kilograms. The method must verify that adding the box will not violate the maximum load. If a violation occurs the box is rejected by returning the value of false; otherwise the weight of the box is added to the vehicle load and the method returns true.
Hint: you will need to use an "if" statement. Here is the basic form of the conditional form: if ( <boolean_expression> ) {
<statement>*
} else {
<statement>*
}
Note that all of the data are assumed to be in kilograms.
Read the TestVehicle.java code. Notice that the code can not modify the load attribute directly, but now must use the addBox method. This method returns a true or false value which is printed to the screen. Compile the Vehicle and TestVehicle classes. Run the TestVehicle class. The output generated should be:
Creating a vehicle with a 10,000kg maximum load.
Add box #1 (500kg) : true
Add box #2 (250kg) : true
Add box #3 (5000kg) : true
Add box #4 (4000kg) : true
Add box #5 (300kg) : false
Vehicle load is 9750.0 kgVersion 3: Change Internal Representation of Weight to NewtonsNow suppose that you were going to write some calculations that determine the wear on the vehicle's engine and frame. These calculations are easier if the weight of the load is measured in newtons. Change your working directory to mod02/exercise2/version3. Create a class Vehicle that implements the above UML diagram.
You may wish to copy the Vehicle.java file you created in version #2.
Modify the constructor, getLoad, getMaxLoad, and addBox methods to use a conversion from kilograms (the parameter weight measurement) to newtons (the instance variable measurement). You might want to use the following private methods:
private double kiloToNewts(double weight) {
return (weight * 9.8);
}
private double newtsToKilo(double weight) {
return (weight / 9.8);
}Note that now the internal data of the vehicle objects is in newtons and the external data (passed between methods) is still in kilograms.
Read the TestVehicle.java code. Notice that it is identical to the test code in version #2. Compile the Vehicle and TestVehicle classes. Run the TestVehicle class. The output generated should be:
Creating a vehicle with a 10,000kg maximum load.
Add box #1 (500kg) : true
Add box #2 (250kg) : true
Add box #3 (5000kg) : true
Add box #4 (4000kg) : true
Add box #5 (300kg) : false
Vehicle load is 9750.0 kg
You should see no change in the output of the program. This demonstrates that the (private) internal changes to the version #3 Vehicle class did not change the code of the client class TestVehicle.
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