Gregory M. Kapfhammer
Past: Using and modifying Java classes!
Future: Writing our own Java classes!
An object has state, defined by values of attributes
An object has behavior, defined by the operations
We can define two classes: Die and RollingDice. Why?
Run the git pull command in your "share" repository!
Now, find the class/source/chapter04/ directory.
Use GVim to study the source code of this system.
Draw a picture to explain how you understand this code.
Compile and run this program. What is the output?
Find all of the following parts of Die and RollingDice!
Data declarations
Method declarations
Constructor declaration
Instance data
Main method
An object should be self-governing
It should be difficult to "reach in" to instance data
Why is this an important issue to enforce?
Let's review Figure 4.5 on page 169!
Visibility modifiers: public and private
See Figure 4.6 to understand the impact of visibility!
This about methods as either accessors or mutators
Run the git pull to get new code!
Review the source code of Transaction and Account
What is the purpose of a return statement?
Please find at least two return statements in the code
Type of the return = type of the returned variable
Please find the parameter list for one of the methods
What do you notice about each entry in the parameter list?
Wait! Let's find the formal and actual parameters
What is the purpose of formal and actual parameters?
Methods can also define local data. Can you find any?
Make sure that you fully understand the working example!
A constructor is invoked when an object is created
The name of the constructor is the same as the class
The constructor returns the type of the class itself
The return type of the constructor is not explicitly stated
The default constructor already exists!
But, it makes an object without assigning values
Please think about the initial state of your objects!
Can you find a constructor in the provided source code?
Created in the same was a other objects
You still interact with them by calling methods
Organize the drawing of distinct visual objects in methods
Refer to the lab assignment and Section 4.9!
Three kinds of objects: components, events, listeners
The focus is on event-driven programming
What kinds of GUI components are available?
Section 4.8: you can add buttons!
Section 4.9: what about text fields?
But, there are also sliders, menus, and others!