More on Classes

1
More on Classes

• Chapter 7

2
Overloading Methods

• Ability to allow different methods or
  constructors of a class to share the same name.
• Two methods or constructors in the same class can
  share names but they MUST have different
  signatures.
• The compiler determines which method to call
  depending the on signature of the method
• (parameters)
• Operator overloading
• Built in with primitives data types
• Expansion allowed in C
• Not allowed in Java

3
Examples of Overloading Methods

• class Point
• doubled x, y
• Point ( )
• x 0.0 y 0.0
• double distance (Point other)
• double dx this.x other.x
• double dy this.y other.y
• return Math.sqrt (dx dx dy dy)

• double distance (double x, double y)
• double dx this.x x
• double dy this.y y
• return Math.sqrt (dx dx dy dy)
• double distance (int x, int y)
• double dx this.x (double) x
• double dy this.y (double) y
• return Math.sqrt (dx dx dy dy)

4
Parameter Passing

• Passed by value
• All parameters of methods
• Usually a method passes back a value through the
  return value
• Passed by reference (objects)
• Values are actually changed
• in-out parameters
• Final Parameters
• Values are not allowed to be changed

5
Recursion

• Java supports recursion
• Recursion the attribute that allows a method to
  call itself

6
Member Modifiers

• Public
• Is accessible by any class
• Protected
• Is accessible by classes\subclasses all classes
  within the same package
• Private
• Is accessible only by the class itself

• Static
• A static field Shares all instances of the class
• Final
• Can not be overridden in subclasses
• BY METHODS ONLY
• Abstract, synchronized, native
• BY FIELDS ONLY
• Volatile transient

7
The main( ) Method

• An application in Java must have a main method
• Must be public
• In order for the JVM (Java Virtual Machine) to
  have access to the application
• Must be declared static
• No object created to run application (cant be
  invoked no other way)
• Public statis void main(String args)
• // BODY

8
Accessing Shadowed/HiddenFields

• public class Point
• public double x, y
• public Point ( )
• public Point (double x, double y)
• this.x x this.y y
• Public void adjust Position ()
• double x this.x, y this.y
• //do calculation using the local x and y
• //commit the changes when done
• this.x x this.y y
• // other methods

9
Passing Object Instances

• public class Department
• protected String name
• protected Faculty facultyList new Faculty
  100
• protected int numOfFaculty 0
• public Department (String n)
• name n
• public void newFaculty (String name)
• facultyListnumOfFaculty new Faculty (name,
  this)
• // other methods

• public class Faculty
• protected Department dept
• protected String name
• public Faculty (String n, Department d)
• name n dept d
• public Department getDepartment ( )
• return dept
• // other methods

10
Understanding Static

• Reserved word static
• They can only call other static methods
• They must only access static data
• They cannot refer to this or super in any way

11
Understanding final

• Reserve word - final
• When used with variables it will not allow the
  variable to be changed
• Similar to a constant (const) in C
• final int num 3
• It can be used with methods, prevents methods
  from being over righted by subclasses
  (inheritance)

12
Nested and Inner Classes

• It is possible to define a class within another
  class.
• A nest class has access to the members, including
  private members, of the class in which it is
  nested.
• The enclosing class does not have access to the
  members of the nested class.
• A class may be declared in a method as well
• The nested and inner class should not be

13
Arrays Revisited

• Arrays are objects
• A member of this class is length that a
  programmer may use

class Length public static void main (String
args ) int a1 new int10 int a2
3, 5, 7, 1, 8, 99, 44, -10 int a3 4,
3, 2, 1 System.out.println(length of a1
is a1.length) System.out.println(length of
a2 is a2.length) System.out.println(length
of a3 is a3.length)
14
More on Strings

• Strings are objects
• Build in member
• length
• Java defines one operator for String
• concatenation
• System.out.println( 3 8 Plus some string)
  System.out.println( 3 8 Plus some
  string)
• System.out.println(Plus some string 3 8)
• System.out.println(Plus some string (38))

15
Command-line Arguments

• java CommandLine this is a test 100 -1
• class CommandLine
• public static void main (String args )
• for(int i0 Iltargs.length I)
• System.out.println(args i
  argsi)