As our Java programs begin to get bigger and we begin to have multiple Objects and Classes that interact with each other, the concepts of access and scope come into play. To oversimplify things, the concepts of access and scope both center around what parts of your programs can interact with specific variables or methods from other parts of your program. Let’s take a brief look at some of the concepts we’ll cover:
Access
- The
publicandprivatekeywords and how they relate to Classes, variables, constructors, and methods - The concept of encapsulation
- Accessor methods, sometimes known as “getters”
- Mutator methods, sometimes known as “setters”
Scope
- Local variables vs. instance variables
- The
thiskeyword
Let’s get started!
Instructions
For now, let’s get a preview of how access works in Java. In the code editor, you should see two files - Bank.java and CheckingAccount.java. Take a look at each file and notice the instance variables are declared using the private keyword. When you’re ready, select the Bank.java file, and run your code.
You should get two errors! Take a look at the main() method in Bank.java. Our Bank is trying to access some instance variables from a CheckingAccount that is marked as private! Take a look at the error message to see which variables are giving us trouble.