My Matlab Presentation (Classes)

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@BankAccount \ accessing the data
function ans = getBalance(ba) % get the balance ans = ba.balance;
Ugly syntax that writes the new account back to the calling program
Object Oriented Programming (OOP) with Matlab
Matlab Classes and Objects
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The Matlab Language
Learning Objectives Building your own classes Making Matlab Classes • • Basic Contents of a Class Deriving child classes
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@BankAccount\deposit.m && withdraw.m
function deposit(acct, amount) % deposit to the account setBalance(acct, acct.balance + amount); assignin('caller', inputname(1), acct); Ugly syntax that writes the new account back to the calling program function gets = withdraw(acct, amount) % withdraw from the account Call local method to set gets = amount; the balance if gets > acct.balance gets = acct.balance; end setBalance(acct, acct.balance - gets); assignin('caller', inputname(1), acct);
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OBJECTS are constructed from the plans for the CLASS.
The Base Class BankAcetBalance
balance
deposit withdraw setBalance
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Structure of a Matlab Class
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Structure of a Matlab Class (cont)
• The following methods are required for all classes to be stored in its main directory: – The Constructor – a method named the same as the class [(Fred) in our example] that consumes initialization data and produces the initial data structure – display.m – the method called whenever Matlab wants to display the contents of an object – char.m – a method returning a character string describing this object • Any other methods required to manipulate the data for this object are also stored here. – set/get methods to access each data item [actually, for child classes, but a good general principle]
function setBalance(acct, amount) % set the account balance acct.balance = amount; assignin('caller', inputname(1), acct);
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Using the BankAccount Class
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@BankAccount\display.m && char.m
function display(ba) % disp for the BankAccount class % displays string representation of the account disp(char(ba));
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@BankAccount\BankAccount.m
Name of the class (matches function acct = BankAccount(data) the file and directory name) % BankAccount class constructor. % ba = BankAccount(amt) creates a bank account Must provide for being called as % with balance amt just BankAccount % could also be a copy contructor: % ba = BankAccount( oba ) copies the account oba if nargin == 0 local data is a structure acct.balance = 0; acct = class(acct,'BankAccount'); elseif isa(data, 'BankAccount') Change the type of the local acct = data; data to the class name else acct.balance = data; acct = class(acct,'BankAccount'); end If the parameter is a BankAccount, just copy it
Many OBJECTS can be constructed and each Instance contains its own set of data and methods.
The CLASS provides the plans for the objects to be constructed.
function s = char(ba) % toString for the BankAccount class % returns string representation of the account s = sprintf( 'Basic Bank Account with $%8.02f\n', … ba.balance );
SavingsAccount
Stored in @SavingsAccount RATE MIN_BALANCE
calcInterest
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Coding Derived Classes - Constructor
function acct = SavingsAccount(data) % SavingsAccount class constructor. % sa = SavingsAccount(amt) creates a savings % account with balance amt % could also be a copy constructor: Create an instance of % sa = SavingsAccount( osa ) the parent class % copies the account oba if nargin == 0 parent = BankAccount; acct.RATE = 5; acct.MIN_BALANCE = 1000; Instantiate local data acct = class(acct,'SavingsAccount', parent); elseif isa(data,'SavingsAccount') acct = data; else Specify the parent parent = BankAccount(data); class for this class acct.RATE = 5; acct.MIN_BALANCE = 1000; acct = class(acct,'SavingsAccount', parent); end
• For simplicity, assume that you have a working directory containing the test scripts for your objects • All methods for a class are stored as Matlab function (.m) files • Methods for a class named Fred are stored in a subdirectory of your working directory named @Fred • The data storage for a class is a structure whose type we force to be the name of the class • The contents of the data structure are initialized and modified by the methods in the class