- Use BlueJ to test a class
(In particular, we will test the BankAccount class that we have just written)
- Make a directory test-BA
in your CS170 directory:
mkdir ~/cs170/test-BA - Save the BankAccount.java
class file in the test-BA directory:
RIGHT click here
and select "Save Target As"
You need to navigate to the directory cs170/test-BA and save the file in that directory.
- Start BlueJ (see lab3: click here )
- From now on, we are working in the
BlueJ
window !!!
- The BankAccount.java
program that you have just saved is not made using
BlueJ
- In order for BlueJ to work with the
BankAccount.java program file,
it needs to make a number of
information files for itself on the
BankAccount.java Java program file.
- So do this first (in the BlueJ window):
- Click Project
Select Open Non-BlueJ... - Navigate to your cs170/test-BA
directory
Click Open in BlueJ
- You should see the following screen:
- When you list the directory cs170/test-BA,
you will see what BlueJ
has created:
ls ~/cs170/test-BA >> BankAccount.java bluej.pkg
The bluej.pkg contain information used by BlueJ
- Click Project
- Now compile the class (click on the "Compile" button - it's located on the left hand size in the figure above)
- As discussed above, you need to
construct some objects
before you can "test drive" the functions of the object
- We will construct 2 BankAccount,
one using the
default constructor BankAccount()
and the second one using the
constructor BankAccount(double initialBalance)
- Here is how to construct a BankAccount
object named
harrysChecking
using the
default constructor BankAccount()
- Right click on the BankAccount
class
- Select
new BankAccount()
(the defaukt constructor)
- Enter the Name of Instance:
harrysChecking
- You should see this in the screen:
- Click OK and you should see this:
- The red box named harrysChecking represents the BankAccount object
- Now, right click on harrysChecking
and select Inspect
and you should see this window:
- The Object Inspector shows you the values of the instance variable (which will be changed when you manipulate the object by using its methods !)
- Right click on the BankAccount
class
- Next, we construct a BankAccount
object named
momsSaving
using the
constructor BankAccount(double initialBalance)
- Right click on the BankAccount
class
- Select the
new BankAccount(double initialBalance)
- Enter the Name of Instance:
momsSaving
- Enter the parameter (...):
500
- You should see this in the screen:
- Click OK and you should see this:
- The red box named momsSaving represents another BankAccount object
- Now, right click on momsSaving
and select Inspect
and you should see this window:
- You should see 500 for balance...
- Right click on the BankAccount
class
- Next, we will learn to invoke the
deposit method
and check for the results.
- To deposit $100 in
harrysChecking ,
we would execute:
harrysChecking.deposit(100);
- Without
BlueJ ,
we would have to write a test program
and run it (see: click here)
- With
BlueJ ,
we can invoke the
deposit ,
on an object by clicking on the object.
- So, if we want to execute:
harrysChecking.deposit(100);inside BlueJ , we do:- Right click on the
harrysChecking
object
- Select the method to invoke, which is:
void deposit(double amount)
- You will see a pop-up window that you need to fill in the
value of the parameter:
- Fill in 100 (because we want to execute
harrysChecking.deposit(100); )
and click OK.
- Check the Object Inspector window for
harrysChecking ;
and you should see amount changed to 100.0:
- Right click on the
harrysChecking
object
- Similarly, if we want to invoke:
momsSaving.deposit(300);inside BlueJ , we do:
- Right click on the
momsSaving
object
- Select the method to invoke, which is:
void deposit(double amount)
- You will see a pop-up window; and now you fill in the
value 300 in the parameter
- Click OK.
- You should see the balance in the momsSaving object change to 800.
- Right click on the
momsSaving
object