TCU CoSc 10403 Introduction to Programming (with Java)

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TCU CoSc 10403 Introduction to Programming (with
Java)

• Getting to Know Java

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Problem Solving

• The purpose of writing a program is to solve a
  problem. Problem solving consists of multiple
  steps
• Understanding the problem.
• Breaking the problem into manageable pieces.
• Designing a solution.
• Implementing the solution.
• Testing the solution and fixing any problems that
  exist.

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The Java Programming Language

• A programming language defines a set of rules
• That determine exactly how a programmer can
  combine words and symbols of the language into
  programming statements.
• Programming statements are the instructions that
  are carried out when the program is executed.
• Java is an object-oriented programming language
  (more about that later).
• Java is one of the fastest growing programming
  technologies of all time.

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Reasons Why Java is Popular

• Java is the first programming language to
  deliberately embrace the concept of writing
  programs that can be executed on the Web.
• Moreso, Java is a useful general purpose
  programming language.
• The Java language is accompanied by a library of
  extra software that we can use when developing
  programs.
• The library provides the ability to create
  graphics, communicate over networks, and interact
  with databases.
• The set of supporting libraries is huge and
  versatile.

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Ive been telling you that Java is an Object
Oriented Programming Language - what exactly does
that mean?

• To understand - we need to discuss and understand
  what an Object is and how it relates to a Class!!

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Anatomy of a Java class
A class is a description of a template (or
pattern) that specifies the types of data values
that an instance of the class can hold and the
operations that it can perform. In OOP, rather
than describe each and every object, the
programmer describes the general type of an
object (a class) and then uses the class to
create (or instantiate) as many of the objects as
are needed. Example a class describinggeneric
students at TCU. Instance variables - the data
that is maintained for students (ex., name,
address, age, ) Constructors - methods that are
involved in the construction of an instance of a
class. Methods - subprograms that permit
instance variables to be accessed and modified
(ex., setName(), setMajor(), getAge(), setAge(),
)
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Example consider a banking problem
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Lets discuss these concepts further!!

• A class -- the basic building block of an
  object-oriented language.
• It is a template/pattern that describes the data
  and behavior associated with instances of that
  class.
• When you instantiate a class you create an object
  that looks and feels like other instances of the
  same class.
• The data associated with a class or object is
  stored in instance variables
• the behavior associated with a class or object is
  implemented with methods. Methods are similar to
  the functions or procedures in other procedural
  languages.
• Some author wrote Julia Child's recipe for
  rack of lamb is a real-world example of a class.
  Her rendition of the rack of lamb is one instance
  of the recipe, and mine is quite another. (While
  both racks of lamb may "look and feel" the same,
  I imagine that they "smell and taste" different.)

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Constructors

• A constructor
•  
• is a special method that is used to set up a
  newly created object
• often sets the initial values of variables
  (i.e., it can be passed information that can be
  used to initialize some variables in the object)
• has the same name as the class
• does not return a value
• has no return type, not even void
•  
• The programmer does not have to define a
  constructor for a class (there is a default
  constructor for every class its syntax is
• theNameOfTheclass()
• For example, a class named Student could have a
  constructor that receives a parameter specifying
  the Students name
• Student tommy new Student(Tom Jones)

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Inheritance

• Classes are defined in a hierarchy
• A class can extend (inherit from) some other
  class
• Object gt Component gt Container gt Panel gt
  Applet
• Thus, an Applet can do everything that Panel does
  and some other things. A Panel can do everything
  a Container can do, etc
• Advantage
• Easy to extend or specialize something that
  already exists. Note we take advantage of this
  when we write
• public class HelloWorld extends Applet
• Disadvantage
• Sometimes difficult to find everything that a
  class does you may have to look up the tree.

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Inheritance

• One class can be used to derive another via
  inheritance.
• A class can extend (inherit from) some other
  class

Subclasses or derived classes - may have more
than just 2 levels.
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Java Components

• Package (what the import statement brings in!!)
• collection of related classes
• Class
• description of an object (template)
• variables methods
• Variable name for memory location for a data
  item
• Method specifies an action on an object
• retrieve/return info or change info
• Object
• instance of a class
• created by the new operator
• Java program collection of cooperating objects

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Creating Objects
jackSmith

• The new operator creates a new object from a
  class
• Example
• Person jackSmith new Person ()
• Person sallyJones new Person()
• This declaration asserts that jackSmith and
  sallyJones are variables that refer to objects
  created from the Person class.
• They are initialized (set to point) to the
  objects created by the new operator
• The newly created object is actually created and
  allocated to memory by a call to a very special
  method contained within the class - a constructor
  of the class.

Instance of the Person class containing a copy of
all instance variables and all methods
sallyJones
Instance of the Person class containing a copy of
all instance variables and all methods
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Choosing Identifier Names

• Identifier names should be descriptive.
• Avoid meaningless names such as a or x.
• Unless the name is actually descriptive, such as
  using x and y to represent (x, y) coordinates.
• Avoid using unnecessarily long names (unless they
  promote better readability - example
  yearToDateSalary).
• A name in Java is a series of identifiers
  separate by the dot (period) character.
• The name System.out is the name of an object
  through which we invoke the println method.
  (println is a method inside the object.)