Comp 14 decomposition overloading relationships
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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…)

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  • Midterm exam is on Friday

  • Review tomorrow


  • 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)


  • What is encapsulation?

  • What is an abstraction?

  • What are the visibility modifiers and what do they do?

  • How is a method declared?


  • Constructors

  • Object relationships

  • Method overloading

  • Method Decomposition


  • 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.


  • 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
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 relationships1
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

  • 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 overloading1
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

Method overloading2

Version 1

Version 2

float tryMe (int x, float y)


return x*y;


float tryMe (int x)


return x + .375;



result = tryMe (25, 4.32)

Method overloading

Overloaded methods
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
Overloading constructors

  • Constructors can be overloaded

  • An overloaded constructor provides multiple ways to set up a new object

Method decomposition
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
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