Java OOP Course: Control Flow, Classes, Arrays, Inheritance, and More - Prof. David M. Mou, Study notes of Computer Science

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Object Oriented Programming: In this course we began an introduction to programming

from an object-oriented approach.

• Java was the primary vehicle we used for programming.
• This will continue in CMSC 132 where you will learn more of the finer points of object- oriented design.

Major Topics :

Basic Elements : types, variables, constants, operators, I/O Control Flow : if-else, switch, while, do-while, for Classes :

• object instances and references
• instance and class data
• methods Arrays : 1-dim, multi-dim, ragged arrays, programming Inheritance : overriding, late-binding, interfaces

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Basic Elements :

• Basic file structure : File name, class structure, comments
• Identifiers : Naming rules and naming conventions.
• Primitive types :
  • boolean
  • Integral types : byte, (char), short, int, long
  • Floating point types : float, double
• Strings : and common String operators/methods.
• Specifying constants : true, ‘x’, 12, 3124L, 3.14159e-
• Operators : Their meaning and precedence rules.

Possible Questions :

• Are these valid identifier names? $Pasta_Fazool
• Operator precedence : x * 2 + y --
• Is a cast needed? float y = 2.0;

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Control flow :

• Conditionals : if-else, switch
• Loops : while, do-while, for
• Jumps : break and continue

Possible Questions :

• Trace the loop : for ( int i = 4; i < 10; i += 3 ) { … }
• Combining loops and conditionals : Is a string a palindrome?
• Combining loops with arrays : Insert an item into a sorted array.
• Nested conditionals : Given x, y, and z, return the smallest.
• Nested loops : Selection, Insertion, Bubble Sort.

Avoid Pitfalls :

• Don’t forget breaks in switch statements.
• Be sure you understand the problem before coding. (If not, ask)
• Test on a example before and after coding.

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Class Objects and References :

• Creating object instances with new
• The null reference
• Java’s class library
• The heap and garbage collection

Basic Class Concepts :

• Instance (non-static) and class (static) variables
• Access modifiers (public, private, protected, default (package))
• Constructors (initializers)

Methods :

• Static and non-static
• Arguments, call-return, and local variables
• Return and memory leaks

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Possible Questions :

• Draw a memory map
• You be the compiler :
  • We declare methods and create some objects, and
  • … ask you which overloaded method is called, or
  • … ask you whether access is valid/invalid
• Class design :
  • we specify the objects and functionality
  • you design the class: instance variables, constructors, methods

Avoid Pitfalls :

• Call the right method : Determine which overloaded function to call, then check its accessibility.
• Read your old programs : Eclipse fills in many things for you automatically. Be sure you can do it on your own.
• Deep/Shallow copy : For a deep copy, create new object instances.

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public class Person { private String name; private int age;

public Person( String n, int a ) { name = n; age = a; }

static void f( String b ) { int x = b.length( ); / STOP HERE / }

public static void main( String[ ] args ) { String[ ] n = {"Bob", "Alice"}; Person p = new Person( n[1], 43 ); f( n[0] ); } }

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Arrays :

• Creating, indexing
• Arrays of primitives and object references
• 2-dimensional arrays and ragged arrays (array of arrays)

Possible Questions :

• Array manipulation :
  • Inserting/Removal/Searching in partially filled arrays
  • Appending/Merging arrays
  • Shifting, rotating, permuting elements in an array
• 2-dim array manipulation :
  • Appending arrays
  • Transposing arrays (inverting rows and columns)

Avoid Pitfalls :

• Allocation : Remember to explicitly allocate array/element storage
• Simplify : Break complex operations into smaller/simpler pieces
• Inside-Out : Design nested loops from the inside-out

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call stack

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Inheritance :

• Terminology : base class (superclass), derived class (subclass), super (parent class)
• Method overriding (vs. overloading), late-binding, and final
• Abstract methods and abstract classes (derived class implements) and polymorphism
• up- and down-casting , getClass and instanceof
• Multiple inheritance and interfaces

Possible Questions :

• Be the compiler : We give code. Which method is called?
• Design : We give the specs, you design the classes and methods.

Avoid Pitfalls :

• Overriding only occurs when prototypes are identical. Start at the declared class, and go to the derived class if overriding applies.

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Miscellaneous Topics :

• Javadoc : @tags and their usage: @author, @param, @returns, …
• Java Class Library : Math, DecimalFormat, ArrayList, …
• Packages :
  • Organizes Java files into groups (directories)
  • Packages may be subdivided into subpackages
  • You have access to names in your own package or packages you import.
• Exceptions :
  • try-catch blocks and exception propagation

Possible Questions :

• Know common methods for String and ArrayList. For others know the basic concepts (Stack: push, pop, peek) but not details.
• Package : What is accessible with/without importing?
• Exception : Design/trace try-catch blocks.

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CMSC 132 : You will learn more about object oriented programming in greater depth, still in

Java.

• More on software testing (JUnit) and debugging
• I/O and exceptions
• Recursive functions
• Linked data structures
• Networking

CMSC 212 : Low-level programming concepts

• C programming
• Memory allocation and deallocation
• Internal representations of arrays and data structures

CMSC 250, 351 : Discrete math and algorithm design

CMSC 311 : Computer organization (“what’s inside”)

CMSC 330 : Programming languages