Introduction to Programming with Java

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Introduction to Programmingwith Java

• Anatomy of an Class

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A Counter Class
public class Counter private int count
public Counter () count 0
public int getCount() return count
public void inc() count count 1
// add code for a reset method
state instance variable(s)
constructor(s)
methods
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How to Create Classes, Objects

• Type code for the class in DrJavas main pane
• Save the code in a file with the same name as the
  class(e.g. Counter.java)
• Compile it (choose the option to Save on Compile)
• Successful compilation creates an additional
  .class file, which contains Java bytecode (e.g.
  Counter.class)
• Now you can create an object with the new
  operator
• gt Counter c1
• gt c1 new Counter()
• gt c1.inc()

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Each Object Has Its Own State

• gt Counter c1
• gt c1 new Counter()
• gt c1.getCount()
• 0
• gt c1.inc()
• gt c1.getCount()
• 1
• gt // create another counter
• gt Counter c2 new Counter()
• gt c2.getCount()
• 0
• gt c1.getCount()
• 1

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Anatomy of a Class
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What is a Method?
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What Can a Method Do?

• Change its objects state
• Report its objects state
• Operate on numbers, text, files, graphics, web
  pages, hardware,
• Create other objects
• Call another objects method obj.method(args)
• Call a method in the same classthis.method(args)
  
• Call itself (recursion)
• And much more, as well see!

Advanced A static method pertains to a class
vs. an individual object.
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Method Declaration

• public return_type methodName(0
  parameters)..
• public int getMiles() ..
• public void increaseSpeed(int accel, int
  limit)..
• Name Verb starting with a lowercase letter, with
  camel caps
• Ouput Return type required.
• Input 0 or more parameters
• Body
• Enclosed by curly braces
• Contains an arbitrary of statements
  (assignment, if, return, etc.).
• May contain local variable declarations
• How its called dot operator
• objectName.methodName(arguments)
• cab1.increaseSpeed(5, 65)

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Getter and Setter Methods
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A Methods Input

• A method may receive 0 or more inputs.
• A method specifies its expected inputs via a list
  of formal parameters (type1 name1, type2 name2,
  )
• In a method call, the number, order, and type of
  arguments must match the corresponding
  parameters.

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Method Output

• A method may output nothing (void) or one thing.
• If it outputs nothing
• Its return type is void
• public void setMiles(int miles)..
• If it outputs one thing
• Its return type is non-void (e.g int, boolean,
  Taxi)
• public int getMiles()..
• It must have a return statement that returns a
  value
• // value returned must match return type
• return miles

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What is a Constructor?
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A Class with Two Constructors
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Constructor Method Review
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Anatomy of a Class