Methods

1
Methods

• Chapter 6

2
Program Modules in Java

• What we call "functions" in C are called
  "___________________" in Java
• Purpose
• Reuse code
• Modularize the program
• This can be done by putting the code in a method
• Various objects in a program can invoke the same
  method

3
Predefined Methods

• The Math class
• These methods are called by
• The __________ of the class
• The dot . operator
• The name of the _____________
• Exampledouble x Math.sqrt(900.0)

4
Method Declaration Syntax

• modifiers returnType methodName
  (parameterDeclaration)
• statements
• modifiers describers (____________________,
  etc.)
• returnType type of value returned by method, or
  __________ if it does not return a value
• methodName identifier that names the method
• parameterDeclaration list of parameters,
  separated by ______________________
• statements define the behavior of the method

5
Argument Promotion

• Coercion of arguments
• Forcing arguments to appropriate type to pass to
  method System.out.println( Math.sqrt( 4 ) )
• Evaluates Math.sqrt( 4 )
• Then evaluates System.out.println()

6
Argument Promotion

• Promotion rules
• Specify how to ______________ types without data
  loss

7
Method Definitions

• Consider a method to square a number public int
  square( int y )
• return y y // return square of y
• // end method square
• We will place it in an ____________SquareIntegers
  .java

8
Method Definitions

• Consider a method to find the maximum of three
  numbers in an adapted version of Figure 6.4
• Note
• It is an _____________
• The maximum function must be __________
• ____________ not needed

9
Java API Packages

• Predefined classes grouped into categories of
  related classes
• Called ________________
• Called the Java Application Programming Interface
  (API)
• Note the often used API packages

10
Random-Number Generation

• Consider the random method in the Math class
• Generates a random double 0 lt n lt 1.0
• The number can be manipulated and ____________ as
  an int to get desired range
• For the roll of a die1 (int) (Math.random()
  6)
• Note Figure 6.7 and Figure 6.8

11
Game of Chance

• Rules for "Craps"
• Roll dice first time
• If sum equals 7 or 11, the player wins
• If sum equals 2, 3 or 12, the player loses
• Any other sum (4, 5, 6, 8, 9, 10) is that
  players point
• Keep rolling dice until
• Sum matches player point
• Player wins
• Sum equals 7
• Player loses

12
Game of Chance

• Note the adapted version of Figure 6.9
• An application
• Note
• ___________ class variables
• Public ____________
• The toUpperClass function requires Character. (a
  _________________ class)

13
Scope of Declarations

• Scope of a parameter is body of __________ where
  declaration appears
• Scope of local variable is from point of
  declaration to ______________
• Scope of label in labeled break/continue is
  statement enclosed by labeled statement
• Scope of local-variable in initialization of for(
  ) is for ___________ of for and rest of header
• Scope of method or field of class is body of class

14
Methods of Class JApplet

• public void init()
• Called once by ____________ container when applet
  loaded
• Initializes fields, creates GUI components, load
  sounds, images
• public void start()
• Called ________________ init
• Completes execution
• Called again if browser _______________ to this
  page

15
Methods of Class JApplet

• public void paint (Graphics g)
• Called after init finishes and start has started
• Called each time applet needs to be
  ______________
• Typical actions include drawing with Graphics
  object g passed to the method
• public void stop()
• Called when applet should stop (when browser
  leaves the HTML page)
• Performs tasks to suspend applet's execution
• public void destroy()
• Called when applet is being removed from memory
• Destroys resources allocated to the applet

16
Method Overloading

• Multiple methods with same name can be declared
  in same class
• Methods must have different signatures
• Different numbers, types, order of parameters
• Example
• Figure 6.12
• Multiple square methods

17
Recursion

• Recursive method
• Calls itself (directly or indirectly) through
  another method
• Method knows how to solve only a base case
• Method divides problem
• Base case
• Simpler problem Method now divides simpler
  problem until solvable
• Recursive call
• Recursive step

18
Recursive Evaluation of 5!
Final value 120

5! 5 24 120 is returned
2! 2 1 2 is returned
5 4!
5 4!
4! 4 6 24 is returned
4 3!
4 3!
3! 3 2 6 is returned
3 2!
3 2!
2 1!
2 1!
1 returned
(b) Values returned from each recursive call.
(a) Sequence of recursive calls.
19
Recursive Factorial Program

• Function factorial() in Figure 6.15
• Note
• Initial call to factorial()
• Anchor or base case
• Recursive call

20
Recursive Fibonacci Program

• Consider function from program   public long
  fibonacci( long n )         // base case     
  if ( n 0 n 1 )           return
  n      // recursive step      else        
  return fibonacci( n - 1 ) fibonacci( n - 2
  )     // end method fibonacci
• Note why this would be extremely inefficient

21
Recursive Fibonacci Program
fibonacci( 3 )
return

fibonacci( 2 )
fibonacci( 1 )
return

return 1
fibonacci( 1 )
fibonacci( 0 )
return 0
return 1
22
Recursion vs. Iteration

• Both the recursive functions shown can be done
  with either for or while loops
• In fact they are done more efficiently
  iteratively
• Recursion has overhead
• Processor time
• Memory space
• General rule If it can be done either
  recursively or iteratively choose iteratively