Interfaces and Nested Classes - Multimedia Introduction to Programming Using Java - page 345

not need to know about it. Further, it would be nice to structure the program so
that Transaction s for an account are connected more closely to that account
instead of using a field account to indicate which account it is.
To do this, we make class Transaction an inner class of BankAccount , as
shown in Fig. 12.14. You already know that non-static fields account and bal-
ance belong in each instance of BankAccount . Since class Transaction is also
nonstatic, a file drawer for it also belongs in each instance of BankAccount .
Since each instance of Transaction is within a Transaction file drawer,

Get the class
of Fig. 12.15
from lesson
page 12.6.

/** A bank account */
public class BankAccount {
/** a ccount number, amount in account, and last transaction carried out
("deposit" or "withdrawal" */
private int account;
private int balance;
private Transaction lastTransaction;

// Getter and setter methods omitted.

/** Deposit amount in this account */
public void deposit( int amount) {
balance= balance + amount;
lastTransaction= new Transaction(amount, "deposit");

}

/** Withdraw amount from this account */
public void withdraw( int amount) {
balance= balance - amount;
lastTransaction= new Transaction(amount, "withdrawal");

}

/** A bank-account transaction */
private class Transaction {
/** type of transaction ( "deposit" , "withdrawal") and amount */
String transaction;
int amount;

/** Constructor: instance for this account, kind t , amount n */
public Transaction( int n, String t)
{ transaction= t; amount= n; }

/** representation of this Transaction */
public String toString()
{ return account + ": " + transaction + " " + amount; }

}

}
Program 12.14:

Class BankAccount , with inner class Transaction