Decorator Pattern Confusion

[Prithvi Sehgal]

Hi,

I am trying to study Decorator pattern from Head First Design Patterns but i am unable to understand the basic concept,
can please someone point me towards a compact article or describe decorator pattern with an example.

BR,

[Jimmy Clark]

public final class InterestCalculatorImpl implements Calculator {

     public final int calculate() {

     }

}


public final class CalculatorDecoratorImpl {


     private Calculator c;

     public CalculatorDecoratorImpl(Calculator x) {
          this.c = x;
     }
     /** This method "extends" the functionality of the calcuate method of the InterestCalculatorImpl 
       *  without changing any code in the InterestCalculatorImpl class definition
       */
     public final int calculate() {

          // Lines of code that do something
          // more lines of code of functionality here

          int x = c.calculate();

          // Lines of code that do something
          // more lines of code of functionality here

          // x = x+y; Possible change result of calculate method with different values/equations
         
          return x;
}
     }