Inheritance Hierarchies

• Sets of classes can form complex inheritance hierarchies
• Example:

Inheritance Hierarchies Example: Swing Hierarchy

• Superclass JComponent has methods getWidth, getHeight
• AbstractButton class has methods to set/get button text and icon

A Simpler Example: Hierarchy of Bank Accounts

• Consider a bank that offers its customers the following account types
  • Checking account: no interest; small number of free transactions per month, additional transactions are charged a small fee
  • Savings account: earns interest that compounds monthly
• Inheritance hierarchy: 

• All bank accounts support the getBalance method
• All bank accounts support the deposit and withdraw methods, but the implementations differ
• Checking account needs a method deductFees; savings account needs a method addInterest

What is the purpose of the JTextComponent class in Figure 4?

   Answer: To express the common behavior of text fields and text components.

Which instance field will we need to add to the CheckingAccount class?

   Answer: We need a counter that counts the number of withdrawals and deposits.