java enums
Download
Skip this Video
Download Presentation
Java Enums

Loading in 2 Seconds...

play fullscreen
1 / 7

Java Enums - PowerPoint PPT Presentation


  • 150 Views
  • Uploaded on

Java Enums. Why have Choice.Yes and Choice.No ?. Old Way. Enumerated types consist of a set of named values Example: Font has BOLD, ITALIC rather than 1, 2 // From class Font: public static int BOLD = 1; public static int ITALIC = 2;

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about ' Java Enums' - aideen


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
java enums

Java Enums

Why have Choice.Yes and Choice.No?

old way
Old Way
  • Enumerated types consist of a set of named values
  • Example: Font has BOLD, ITALIC rather than 1, 2

// From class Font:

public static intBOLD = 1;

public static intITALIC = 2;

  • It\'s easier to remember Font.BOLD than 1
  • Font.BOLDin action

JButton button = new JButton("Courier 24 point Bold");

button.setFont(new Font("Courier", 24, Font.BOLD));

an int is an int
An int is an int
  • private static ints are also know as "glorified integers"
  • This can lead to problems
    • Can you read the text in the button with a point size of 1?
  • Since Font.BOLD is just an int you can pass in any other int value, like 2314
  • And since the style Font.BOLD is compatible with point size (both int type parameters), you get one (1) point font like above
  • Swap the arguments to get what was intended see next slide
would be nice to have different type
Would be nice to have different type
  • Since Font.BOLD is just an int, you can pass in any other int value, like 2314 or -123
  • And since the style Font.BOLD is compatible with point size (both int type parameters), you get one (1) point font like above
  • Swap the arguments to get what was intended

button.setFont(new Font("Courier",24, Font.BOLD));

button.setFont(new Font("Courier", Font.BOLD, 24));

new way
New Way
  • Use the Java enum type like this

public enumFontStyle{BOLD, ITALIC};

  • The previous attempt to construct a Font would preferable be a compile-time error
  • With an enum type, we get an improved constructor

public Font(String name, FontStyle style, intsize)

an enum used in gametree
An Enum used in GameTree
  • playerSelectedusing a String parameter could result in code like this

public void playerSelected(String yesOrNo) {

if (yesOrNo.equals("Yes"))

; // go left

else if (yesOrNo.equals("No"))

; // go right

else

JOptionPane.showMessageDialog(null,

"Contact vendor!");

}

    • Just hope the user never types "Y", "yes" or "y"
      • and the programmer used equals, not ==
must use a choice argument
Must use a Choice argument
  • Here is the actual design of playerSelected

/**

* Ask the game to update the current node by going left for

* Choice.yes or right for Choice.no Example code:

* theGame.playerSelected(Choice.Yes);

*

* @paramyesOrNo

*/

public voidplayerSelected(Choice yesOrNo) {

if(yesOrNo == Choice.Yes)

; // go left

if (yesOrNo== Choice.No)

; // go right

}

ad