Summary - Exception basics

Combine try/catch/finally and throw to write a bank account class.

Summary - Exception basics

In this group you learned try/catch, finally, throw, the exception hierarchy and multiple catch. You can now write an Account class, use throw for a balance check in withdraw, and handle it with try/catch/finally at the call site.

This summary lesson has 5 steps and includes one code task. The bank account example brings everything you learned together.

Exercise Bank account

Write an Account class: a double balance field, an Account(double b) constructor and a void withdraw(double amount) method. withdraw should throw new IllegalStateException("Yetersiz bakiye") if amount > balance. In main create Account acc = new Account(100); and call acc.withdraw(150); catch IllegalStateException with try/catch and print Hata: with getMessage(); print İşlem tamam in finally.

Show example solution

// inside Account:
void withdraw(double amount) {
  if (amount > balance) {
    throw new IllegalStateException("Yetersiz bakiye");
  }
  balance -= amount;
}
// inside main:
try {
  acc.withdraw(150);
} catch (IllegalStateException e) {
  System.out.println("Hata: " + e.getMessage());
} finally {
  System.out.println("İşlem tamam");
}

Test yourself

When does the finally block run?
- Only when there is an exception
- Only on return
- Always
- Only when there is no exception
Show answer

Always — finally runs in every case, whether or not an exception occurs.

Throw for insufficient balance

if (amount > balance) {
  throw new IllegalStateException("____");
}

Show answer

if (amount > balance) {
  throw new IllegalStateException("Yetersiz bakiye");
}

Match each keyword to its purpose

try

Risky code
catch

Catch error
finally

Cleanup
throw

Throw exception

Next lesson: Project design

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