/*File Intfc01.java Copyright 1997, R.G.Baldwin
Revised 08/12/99
Illustrates use of interface.

The interface definitions for Constants and MyIntfc are 
contained in the files named Constants.java and 
MyIntfc.java.  The compiler requires them to be in separate
source files.

The interface named Constants contains two constants.
The interface named MyIntfc contains declarations for set()
and get().

Different versions of set() and get() are implemented in 
ClassA and ClassB.

The output from running the program is: (manual line breaks
were inserted to make it fit the display format)

Instantiate objA of type ClassA, then set, and show data.
In set() method for classA, using pi from Constants 
  interface: 12.28
In show() method for ClassA, data = 12.28

Assign objA to ref var of type MyIntfc named objAA.
Invoke set() method on objAA to modify the data.
In set() method for classA, using pi from Constants 
  interface: 24.56
Invoke get() method on objAA to display the modified data.
objA data = 24

Instantiate object of type ClassB named objB.  Immediately 
  assign the ref to a type MyIntfc ref var instead of a 
  type ClassB ref var.
Invoke its set() method to store some data.
In set() method for classB, using intConstant from 
  Constants interface: 1375
Invoke its get() method to display the data.
objB data = 1375

Successfully assign objA to objB and display objB
objB data = 24

Invoke set() method on objAA to modify its data.
In set() method for classA, using pi from Constants 
  interface: 98.24
Successfully assign objAA to objB and display objB
objB data = 98

Restore objB to its original type and value.
In set() method for classB, using intConstant from 
  Constants interface: 1375
Successfully assign objB to objAA and display objAA
objAA data = 1375

Attempt to assign objB to objA fails because
  "Explicit cast needed to convert MyIntfc to ClassA."

Attempt to invoke show() method of objAA fails because
"Method show() not found in interface MyIntfc".
End of program.

*/
//=======================================================//
class ClassA implements Constants,MyIntfc{
  double data;
  
  //Define versions of set() and get() appropriate to 
  // ClassA
  public void set(int inData){
    //note use of pi from Constants interface
    data = (double)inData*pi;
    System.out.println(
      "In set() method for classA, using pi from " +
                           "Constants interface: " + data);
  }//end set()
  
  public int get(){
    return (int)data;
  }//end get()
  
  //Define a show method for ClassA not declared in 
  // interface MyIntfc
  void show(){
    System.out.println(
            "In show() method for ClassA, data = " + data);
  }//end show() method
}//end ClassA
//=======================================================//

class ClassB implements Constants,MyIntfc{
  int data;
  
  //Define versions of set() and get() appropriate to 
  // ClassB
  public void set(int inData){
    //note use of intConstant from Constants interface
    data = inData*intConstant;
    System.out.println(
      "In set() method for classB, using intConstant " +
                     " from Constants interface: " + data);
  }//end set()
  
  public int get(){
    return data;
  }//end get()
}//end ClassB
//=======================================================//

class Intfc01{
  public static void main(String[] args){
    System.out.println(
      "Instantiate objA of type ClassA, then set, and " +
                                             "show data.");
    ClassA objA = new ClassA();
    objA.set(2);
    objA.show();    
  
    System.out.println("\nAssign objA to ref var of " +
                              "type MyIntfc named objAA.");
    MyIntfc objAA = objA;
    System.out.println("Invoke set() method on objAA " +
                                    "to modify the data.");
    objAA.set(4);  
    System.out.println("Invoke get() method on objAA to " +
                             "display the modified data.");
    System.out.println("objA data = " + objAA.get());
    
    System.out.println(
      "\nInstantiate object of type ClassB named objB." +
            "  Immediately assign\n the ref to a type " +
            "MyIntfc ref var instead of a type ClassB " +
                                              "ref var.");
    MyIntfc objB = new ClassB();
    System.out.println("Invoke its set() method to " +
                                      "store some data.");
    objB.set(11);
    System.out.println("Invoke its get() method to " +
                                     "display the data.");
    System.out.println("objB data = " + objB.get());

    System.out.println("\nSuccessfully assign objA to " +
                                  "objB and display objB");
    objB = objA;
    System.out.println("objB data = " + objB.get());

    System.out.println("\nInvoke set() method on objAA " +
                                    "to modify its data.");
    objAA.set(16);    
    System.out.println("Successfully assign objAA to " +
                                  "objB and display objB");
    objB = objAA;
    System.out.println("objB data = " + objB.get());
    
    System.out.println("\nRestore objB to its original " +
                                        "type and value.");
    //objB already defined as type MyIntfc
    objB = new ClassB();
    objB.set(11);
    System.out.println("Successfully assign objB to " +
                                "objAA and display objAA");
    objAA = objB;
    System.out.println("objAA data = " + objAA.get());

    System.out.println("\nAttempt to assign objB to " +
      " objA fails because\n  \"Explicit cast needed to " +
                           "convert MyIntfc to ClassA.\"");
    //objA = objB; //statement removed by making it comment
    
    System.out.println(
      "\nAttempt to invoke show() method of objAA fails " +
      "because\n \"Method show() not found in interface " +
                                             "MyIntfc\".");
    //objAA.show();//statement removed by making it 
    // a comment
    
    System.out.println("End of program.");

  }//end main
}//end class Intfc01
//=======================================================//