interface as pointer

[vishwas bhatt]

hi.
this is first time.i hope i will got a perfect answer.
myself preparing java from just JAVA. i have got problem in that
in interface topic there is one line that i don't understand.
"Interface is just like pointer to function in 'c' "
please help
wating for you reply.

[Cindy Glass]

Do you have any c background?? If not you will probably not understand the reference to how something works in c.

[vishwas bhatt]

thanks cindy for your replay.
i have got good c and c++ background. i understand the topin "pointer to function" very well . but i can't match this with interface in java.
please help me.
wating of you replay.

[Cindy Glass]

If you have a class that has an interface, and you are familiar with the methods of that interface, then you know that the new class will have all of those methods.
Implementing the interface "flags" or "points out" to the world that the methods (functions) are available.

[vishwas bhatt]

cindy can you explain me this by giving any example.

[Frank Carver]

Consider this example. We define one interface which is implemented by two classes. Another class may be passed any class which implements the interface, and calls the method defined in the interface. Which implementing class to create and pass in is not known until run-time (chosen by a command-line argument).

/**
 Define the minimum requirements for an object to be a Getter
*/
interface Getter
{
  public Object get();
}
  
class MyGetter implements Getter
{
  private String value;
  
  public MyGetter(String value)
  {
    this.value = "I like '" + value + "'";
  }
  
  public Object get()
  {
    return value;
  }
}
  
class YourGetter implements Getter
{  
  public Object get()
  {
    return "I do not care");
  }
}
public class GetterUser
{
  // This reference doesn't care what sort of Getter it is given, 
  // only that it is given some sort of Getter
  //
  private Getter getter;
  
  public GetterUser(Getter getter)
  {
    this.getter = getter;
  }
  
  public show()
  {
    System.out.println("the value of the getter is: " + getter.get());
  }
  
  public static void main(String[] args)
  {
    // set useYours to true if there is an argument and it is "your"
    //
    boolean useYours = args.length > 0 ? ("your".equalsIgnoreCase(args[0])) : false;
    
    // create a new GetterUser and pass in either My or Your Getter as appropriate
    //
    GetterUser user = new GetterUser(useYours ? new YourGetter() : new MyGetter("Java"));
    
    // show what we got
    //
    user.show();
  }
}

I hope this helps.

[vishwas bhatt]

frank ,
i realy got it...!!! what i want . thank's a lot . thanks.
i got one more problem regarding java I/O . I want some tutorial
for I/O which can teach me i/O on very elementary level (low -level). i am aware about whole hirarchy . but i want more . help
me.
hoping for same response ( thank's again)

[Cindy Glass]

Check the File Access Chapter of this tutorial.
http://developer.java.sun.com/developer/onlineTraining/Programming/BasicJava1/

[vishwas bhatt]

Thanks cindy.
this will help me lot thank's a lot.