Parameter Passing

• A formal parameter is a variable declared in a function heading.
• An actual parameter is a variable or expression listed in a call to
  a function.
• Implicit parameter is the object on which methid is invoked,
  named this.
• Explicit parameters are supplied between paranthesis.

• Java uses "Call By Value":
  A method receives copy of parameter value.


• Non-reference actual parameters are not changed by method call. Example:
  
  

  public class DB
    // ineffective method to calculate dB:
    public static void toDecibell(double x)
    {
      x = 10.0 * Math.log10(x);   // change formal parameter value
    }
  };
  
  .......
  
  power = 100.0;           // 100 Watts. 
  DB.toDecibell(power);    // conversion to dBW fails.  power == 100 after call
  
  

• Object reference actual parameter lets method modify object:
  

  public void copyNameTo(Greeter other)
  {
     other.name = this.name;
  }
  ......
  
  Greeter worldGreeter = new Greeter("World");
  
  Greeter daveGreeter = new Greeter("Dave");
  
  
  worldGreeter.copyNameTo(daveGreeter);