Inheritance Cheat Sheet

What inheritance means

• A subclass extends a superclass to reuse fields and methods.

• It forms an is a relationship. SavingsAccount is a BankAccount.

• Java supports single inheritance for classes and multiple inheritance for interfaces.

Extending a class

class BankAccount {
    protected String name;
    protected int accountNumber;
    protected double balance;

    public BankAccount(String name, int number, double balance) {
        this.name = name;
        this.accountNumber = number;
        this.balance = balance;
    }

    public void deposit(double amount) { this.balance += amount; }
    public void withdraw(double amount) { this.balance -= amount; }
    public String getAccountType() { return "Base"; }

    @Override
    public String toString() {
        return name + " #" + accountNumber + " $" + balance;
    }
}

class SavingsAccount extends BankAccount {
    private double interestRate;

    public SavingsAccount(String name, int number, double balance, double rate) {
        super(name, number, balance); // super must be the first statement
        this.interestRate = rate;
    }

    public void applyBonus() {
        this.balance += 100.0; // can access because parent used protected
    }

    @Override
    public String getAccountType() {
        return "Savings";
    }

    @Override
    public String toString() {
        return super.toString() + " " + interestRate + "%";
    }
}