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Lab 07: Mini Problems

Learning Objectives

Students should

  • be able to use Stream<T> in their code to replace loops.
  • be able to write functional-style code.

Initializing

To get the files, run the following command from your PE node. We recommend creating a new directory called mini to store all your lab mini problems.

1
cp -r ~cs2030s/mini/lab7/ .

The files will only be available on Wednesday, 23 October 2024.

Class Files

We have given you a .class file from a badly written Maybe<T> as well as the functional interfaces used in the directory cs2030s/fp. These class files are compiled on the PE node, so we can only guarantee that they can work on the PE node. They may or may not work on other places especially on other operating systems.

Mini Problem 1

CS2030S AY2022-23 Sem 2 PA2

This mini problem is adapted from CS2030S AY2022-23 Semester 2 PA 2.

You are given two classes: Product.java and Cart.java.

Product.java

Product.java is a class that represents a product in an e-commerce site. Each product has

  • an ID called id, with accessor getID().
  • a price called price, with accessor getPrice().
  • a name called name, with accessor getName().

Cart.java

Cart.java is a class that represents a shopping cart in an e-commerce site. It keeps track the list of products added by the user using an ArrayList. It has three methods

  • int totalCost() that returns the total cost of all items in the cart.
  • long numOfExpensiveItems(int threshold) that takes in a threshold price and return the number of items with the price greater than or equal to threshold.
  • product findByName(String name) that takes in a String representing the product name and return the first product with that name.

Shopping Spree

Rewrite the three methods in Cart.java above using functional style.

Mini Problem 2

CS2030S AY2022-23 Sem 2 PA2

This mini problem is adapted from CS2030S AY2022-23 Semester 2 PA 2.

You are given two classes: Account.java and Bank.java. Additionally, we will be using Pair.java from the notes.

Account.java

Account.java is a class that represents an account in a bank. Each account has

  • an account number called accountNumber, with accessor getAccountNumber().
  • an owner called owner, with accessor getOwner().
  • a balance called balance, with accessor getBalance(), and two mutators: deposit(double amount) and withdraw(double amount).
  • a flag to indicate if an account is closed or not called isClosed, with accessor isClosed().

Bank.java

Our bank is getting more popular and now we need to add more functionalities to it. The board members wants you to implement these methods:

  • double totalMoneyInBank() that calculates the total money in the bank across all accounts; and
  • String allAccounts() that return the details of all active accounts in the bank as a string, sorted based on their account balance.
  • Map<Integer, Account> multiAccounts()that returns a map containing Accounts that belong to someone having multiple bank accounts. The key of the map is the account ID, and the value is the Account object.

Endless Stream of Money!

You implemented these classes using for loops in no time. However, during code review, your manager (who is a big fan of functional programming) told you that these methods should be implemented using Stream for the sake of consistency. After all, you implemented the transfer() method using functional style.

To help you, your manager came up with a method Stream<Account> getAccountStream() that returns a stream of all accounts in the bank. He also gave you the documentation for Java's Stream API. Equipped with the tools given by your manager, replace all for loops in totalMoneyInBank(), allAccounts(), and multiAccounts() using Stream! We have indicated the lines you need to make into functional style as comments in Bank.java.