CiS 260: App Dev I

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CiS 260 App Dev I
Chapter 5 Methods and Classes
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Introduction to Methods

• A method (or ________) is a segment of code that
  performs a specific task.
• Advantages of modular program design
• allows you to focus on a small part of the
  program
• many programmers can work on different methods
• encourages software reuse
• improves the simplicity and readability of
  programs
• Java provides ___________ methods in collections
  of classes called class __________.
• Examples of predefined methods are println(),
  showInputDialog(), setText(), etc.
• The programmer can create his own ___________
  methods in classes he creates.

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Predefined Methods

• An algebraic function looks like f( x ) 2x 5
• f is the name of the function
• 2x 5 is the body of the function
• x is the parameter of the function, any real
  number
• if x 2, we write f( 2 ) and 2 is the argument
  of f
• f(2) 2 2 5 ___.
• Java has a pow(x, y) method in the Math class
• pow is the name of the method
• x and y are the ____________ of the method, both
  of type double
• For the arguments x2 and y3, Math.pow(2, 3)
  means 2 raised to the power 3, or ___
• You often need to use the import statement.

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User-Defined Methods

• Predefined methods are prewritten to perform
  common, basic tasks.
• User-defined methods are ________ designed to
  perform very specialized tasks.
• Two kinds of user-defined methods
• value-returning (returns a result to the calling
  method)
• void (doesnt return a result, just executes)

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Value-Returning Method

• Every method has these five parts
• name (such as pow or myCustomMethod)
• parameter list (in parentheses)
• ______ type of each parameter, like double
• the data type of the returned value, like double
• the program code executed by the method
• The first four above constitute the method
  __________ and the last is called the ______.
• The five components above constitute a method
  definition.
• To use a method in a program, you must code a
  method _______.

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Method Example

• Suppose you wrote the following method
• public static double raiseToAPower (double base,
  double exponent)
• double result 1
• for( int i 1 i lt exponent i )
• result base
• return result
• public and static are modifiers, double is the
  return type, and raiseToAPower is the ______.
• (double base, double exponent) is the parameter
  list and the code inside the s is the ______.

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Class With a User-Defined Method

• public class Power
• public static void main( String args )
• double answer
• answer raiseToAPower( 2,3 ) // method ______
• System.out.println(answer) // displays 8.0
• // end main
• public static double raiseToAPower (double base,
  double exponent)
• double result 1
• for( int i 1 i lt exponent i )
• result base
• return result // return this value to main
• // end raiseToAPower
• // end class

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The Return Statement

• The syntax of a return statement in a method is
  return expr where expr is a variable, constant
  value, or ____________.
• The data type of the value of expr must match the
  _______ type of the method.
• When a return statement executes, the method
  terminates and control goes back to the ________.
• public static double larger( double x, double y )
• double max
• if( x gt y )
• max x
• else
• max y
• return max

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Flow of Execution

• The order of methods in a class doesnt matter.
• When a program executes, the first statement in
  the method ________ executes first.
• When the last statement of a method executes,
  control is passed back to the point immediately
  following the method call.
• For a value-returning method, the value that the
  method returns replaces the method call and
  execution follows immediately after the call.
• A _________statement can be used in a void method
  to exit a method early.
• To call a void method, use methodName()

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Data Types and Parameters

• For primitive data types, variables are passed
  from one method to another by ______ .
• This means methods have their own copies of
  primitive data separate from each other.
• For reference variables (objects or abstract data
  types) variables are passed by __________.
• Therefore, a change in the value for a reference
  variable in one method, automatically changes it
  in any other method.
• Remember that a variable of type String is a
  reference variable (points to a String _______).

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Scope of an Identifier

• The scope of an identifier is that part of the
  program in which it is accessible (________).
• A ______ identifier is declared within a method
  or block and is visible only within that method
  or block.
• When a counter variable is declared in a for
  loop, its scope is limited to the for loop.

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Method Overloading

• In Java, a class can contain several methods with
  the same name.
• However, methods with the same name must have
  different _________________.
• This is called method ____________.
• This makes the naming of methods easier.

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The class String

• In Java, a string is not a variable, but an
  _____.
• The following two statements are equivalent
• String name Lisa Johnson
• name new String( Lisa Johnson )
• name is actually a reference variable that
  contains the address of the String ________.
• A string contains ___ or more characters enclosed
  in double quotes.
• The ________ of the first character in a string
  is 0, of the second character is 1, and so on.

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Methods in the class String

• The method substring() is a member of class
  String.
• Using String name Lisa Johnson
• name.substring(0,4) yields _______
• name.substring(5,12) yields Johnson
• name.indexOf(J) yields ___
• name.charAt(4) yields
• name.equals(Lisa Johnson) yields true
• name.equals(Luke Johnson) yields ______
• name.length() yields ____
• name.replace('i','e') yields Lesa Johnson
• The String object name has access to the String
  methods using the ____ operator.

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Formatting Numbers

• You can format numbers in your program using
  complicated program logic (see p. 226)
• Or you can use Java pre-defined methods
• NumberFormat decimal NumberFormat.getNumbe
  rInstance()
• decimal.setMaximumFractionDigits(2)
• String aDecimalStr decimal.format(19.857)
  //19.86
• NumberFormat percent NumberFormat.getPerce
  ntInstance()
• String aPercentStr percent.format(.857) //
  86
• NumberFormat currency NumberFormat.getCurr
  encyInstance()
• String aCurrencStr currency.format(19.95)
  //19.95

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The Calendar Class

• Calendar today Calendar.getInstance()
• int month today.get( Calendar.MONTH ) 1
  // returns numeric month (1 for Jan, 2
  for Feb, )
• Date todaysDate today.getTime()
• System.out.print( todaysDate ) // prints date
  time
• Calendar dueDate Calendar.getInstance()
• dueDate.set( 2007, 11, 31 ) // due date is
  Dec. 31

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The GregorianCalendar Class

• GregorianCalendar birthDate new
  GregorianCalendar( 1953, 8, 10 )
  // Sept. 10, 1953
• int dayOfWeek birthDate.get( GregorianCalendar.
  DAY_OF_WEEK ) // returns, for
  example, Tuesday
• Long birthTime birthDate.getTimeInMillis()
  // time in milliseconds
• DateFormat longDate DateFormat.getDateInstance(
  DateFormat.LONG )
• String birthDayStr longDate.format( birthDate
  ) // September 10, 1953