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accessor methods & mutator methods

 
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accessor methods & mutator methods
bigdoggy
30 Jan, 2008 - 08:24 AM
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Hi
I am writimg a portion of code which needs to alter the score message here(this portion of code is one part of code for a game) ie I need a meaningfull message to appear in the score message bar of the game and in the title bar of the window. I am struggling with the idea of creatring a variable for storing the score message and then altering the accessor and mutator methods to use this variable, help is much appreciated!
CODE

public class Game
{
  private String message;

  public String getScoreMessage()
  {
    return "A message";
  } // getScoreMessage

  public void setScoreMessage(String message)
  {
  } // setScoreMessage


  public String getAuthor()
  {
    return "Big Doggy";
  } // getAuthor
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GWatt
RE: Accessor Methods & Mutator Methods
30 Jan, 2008 - 08:55 AM
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You do know that if you just set the instance variable message equal to the argument, everything that uses message after that will use the new value, right?
CODE
public void setScoreMessage(String message)
{
    this.message = message;
}
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ajwsurfer
RE: Accessor Methods & Mutator Methods
30 Jan, 2008 - 09:06 AM
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This is a standard Java theme, that forces the programmer to acknowledge what they are doing to data container classes, and it gives the container class the opportunity to add complexity to the data being stored, while keeping the access methods simple. The methods are almost always the same and these two generic functions are used as such:
CODE
  
  public class Game
  {
    private String scoreMessage;
    public String getScoreMessage()
   {
      return this.scoreMessage;
    }

    public void setScoreMessage(String message)
    {
       this.scoreMessage = message;
     }


  public String getAuthor()
  {
     ...
     Game G = new Game();
     G.setScoreMessage("Big Doggy");
     return G.getStoreMessage();
    }

This has a few problems, like on return the instance of the Game class (G) is removed and is not used again, but it shows how the "getter" and "setter" methods are used in a class.
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bigdoggy
RE: Accessor Methods & Mutator Methods
30 Jan, 2008 - 09:06 AM
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QUOTE(GWatt @ 30 Jan, 2008 - 09:55 AM) *

You do know that if you just set the instance variable message equal to the argument, everything that uses message after that will use the new value, right?
CODE
public void setScoreMessage(String message)
{
    this.message = message;
}


Ok, so I need to rename the instance variable. I am baffled on the use of mutator methods and accessor methods,how do I need to alter my code to get the result mentioned above?

Thanks
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bigdoggy
RE: Accessor Methods & Mutator Methods
30 Jan, 2008 - 09:23 AM
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QUOTE(ajwsurfer @ 30 Jan, 2008 - 10:06 AM) *

This is a standard Java theme, that forces the programmer to acknowledge what they are doing to data container classes, and it gives the container class the opportunity to add complexity to the data being stored, while keeping the access methods simple. The methods are almost always the same and these two generic functions are used as such:
CODE
  
  public class Game
  {
    private String scoreMessage;
    public String getScoreMessage()
   {
      return this.scoreMessage;
    }

    public void setScoreMessage(String message)
    {
       this.scoreMessage = message;
     }


  public String getAuthor()
  {
     ...
     Game G = new Game();
     G.setScoreMessage("Big Doggy");
     return G.getStoreMessage();
    }

This has a few problems, like on return the instance of the Game class (G) is removed and is not used again, but it shows how the "getter" and "setter" methods are used in a class.

Thanks for your reply, but what is a 'data container class' and what is the notation 'this.' I have not seen it before. When I compile the code error messages appear saying there is no constructor for Game, Why do I need a constructor here?
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GWatt
RE: Accessor Methods & Mutator Methods
30 Jan, 2008 - 09:47 AM
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Well, every class should have a default constructor that accepts no arguments, so I'm not sure why you get that error. However, I also don't understand why the score message equals "Big Doggy"
I don't think that's a very quantitative score.

Anyway. . .
to define a constructor, you create a method that has the same name as the class.
CODE
public class Game
{
    public Game()    //no return type
    {
    }
}


That's a basic constructor that does nothing.

To create a constructor that actually does something:
CODE
public class Game
{
    private String message;

    public Game(String message)
    {
        this.message = message;
    }
}
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