Encapsulation

1
Encapsulation

• English definition
• to enclose in or as if in a capsule
• Computing
• the process of combining elements to create a new
  entity.
• encapsulation is the inclusion within a program
  object of all the resources need for the object
  to function
• Methods
• Fields
• the object is accessed through its interfaces
• the idea is I will tell you only what I want and
  do what I want

2
Motivation
3
Motivation

• Encapsulation is the American Way
• I respect your privacy of your data
• I will trust you to do what you tell me you will
  do
• Encapsulation a religious commandment
• Thou shalt encapsulate thine objects

4
What is Wrong With This Picture?

• public class myClass
• private int i
• public int j

5
What is Wrong With This Picture?

• public class myClass
• private int i
• public int j
• What can someone do to j?

6
What is Wrong With This Picture?
Start of method

• public void setUpButtons()
• buttonPanel new JPanel()
• c.add( buttonPanel , BorderLayout.CENTER )
  
• bZero new JButton( "0" )
• bZero.setFont( new Font("Sanserif",
  Font.BOLD, 16 ) )
• bOne new JButton( "1" )
• bTwo new JButton( "2" )
• bThree new JButton( "3" )
• bFour new JButton( "4" )
• bFive new JButton( "5" )
• bSix new JButton( "6" )
• bSeven new JButton( "7" )
• bEight new JButton( "8" )
• bNine new JButton( "9" )
• bExit new JButton( "Exit" )
• bClear new JButton( "Clear" )
• bClear.setBackground( Color.blue )
• bClear.setForeground( Color.white )
• bMult new JButton( "" )

bDecPt new JButton( "." )
bDecPt.setFont( new Font("Sanserif", Font.BOLD,
22 ) ) / add the following buttons to
the buttonPanel panel. / buttonPanel.add(
bSeven ) buttonPanel.add( bEight )
buttonPanel.add( bNine )
buttonPanel.add( bFour ) buttonPanel.add(
bFive ) buttonPanel.add( bSix )
buttonPanel.add( bOne ) buttonPanel.add(
bTwo ) buttonPanel.add( bThree )
buttonPanel.add( bZero ) buttonPanel.add(
bDecPt ) buttonPanel.add( bEquals )
buttonPanel.setLayout( new GridLayout( 5, 3, 5,
5 ) ) bDecPt.addActionListener( this )
bZero.addActionListener( this )
bOne.addActionListener( this )
bTwo.addActionListener( this )
bThree.addActionListener( this )
bFour.addActionListener( this )
bFive.addActionListener( this )
bSix.addActionListener( this )
bSeven.addActionListener( this )
bEight.addActionListener( this )
bNine.addActionListener( this )
bExit.addActionListener( this )
bMult.addActionListener( this )
bDiv.addActionListener( this )
bSub.addActionListener( this )
bPlus.addActionListener( this )
bEquals.addActionListener( this )
bClear.addActionListener( this )
End of method
7
What Does Encapsulation Do?

• Forces classes to be independent and hide the
  intricate details from the other classes
• All changes made to the object are made by itself
  (through its methods)
• Encapsulation dictates that
• all the attributes must be private
• all the attributes can be accessed only through
  its methods

8
Why Encapsulate?

• Modular programs
• every class is self-contained
• Code reuse
• classes can reused in other programs
  (plug-n-play)
• Improves code maintainability
• programs can be modified independently
• Enables concurrent development
• developers program to interfaces

9
Why Encapsulate?

• If you still dont believe in encapsulating, do
  it because I told you so!

10
Arrogance!
11
Side-effect of Arrogance!
12
Encapsulation Violations

• Public attributes that other classes can access
  and modify