Java Object Relationships and Method Decomposition

COMP 14: decomposition, overloading, relationships June 7, 2000 Nick Vallidis

Announcements • Midterm exam is on Friday • Review tomorrow

Homework • read 4.1-4.6 • assignment P4 is due next Tuesday! (doing it is a good way to study for the exam…) • e-mail me any questions you'd like me to answer in the review tomorrow (do this before tomorrow morning)

Review • What is encapsulation? • What is an abstraction? • What are the visibility modifiers and what do they do? • How is a method declared?

Today • Constructors • Object relationships • Method overloading • Method Decomposition

Constructors • A constructor is a special method that is used to set up a newly created object • The programmer does not have to define a constructor for a class • There is a "default constructor" automatically created for you that does nothing.

Constructors • When writing a constructor, remember that: • it has the same name as the class • it does not return a value • it has no return type, not even void • it often sets the initial values of instance variables

Object relationships • An aggregate object is an object that contains references to other objects • An Account object is an aggregate object because it contains a reference to a String object (p. 189) • An aggregate object represents a has-a relationship • A bank account has a name

Object relationships • Sometimes an object has to interact with other objects of the same type • For example, we might concatenate two String objects together as follows s3 = s1.concat(s2); • One object (s1) is executing the method and another (s2) is passed as a parameter

Method overloading • Method overloading is the process of using the same method name for multiple methods • The signature of each overloaded method must be unique • The signature includes the number, type, and order of the parameters

Method overloading • The compiler must be able to determine which version of the method is being invoked by analyzing the parameters • The return type of the method is not part of the signature

Version 1 Version 2 float tryMe (int x, float y) { return x*y; } float tryMe (int x) { return x + .375; } Invocation result = tryMe (25, 4.32) Method overloading

Overloaded methods • The println method is overloaded: println (String s) println (int i) println (double d) • The following lines invoke different versions of the println method: System.out.println ("The total is:"); System.out.println (total);

Overloading constructors • Constructors can be overloaded • An overloaded constructor provides multiple ways to set up a new object

Method decomposition • A method should be relatively small, so that it can be readily understood as a single entity • A potentially large method should be decomposed into several smaller methods as needed for clarity • Therefore, a service method of an object may call one or more support methods to accomplish its goal

Guideline for decomp. • A general rule is to make your methods small enough so that they can fit on one screen • Definitely ok to be shorter • can be longer if decomposing it introduces unnecessary complexity

Java Object Relationships and Method Decomposition