• "Black Box" metaphor
• Scope of variables - variables are only recognized inside the block of code where they are defined. Thus a variable defined within a nested block of code is not known outside the inner nest. The same hold true for methods. Varables in one method are not known by variables in other methods. The variables defined by the method are not known by the calling method ( for example main() ).
  So how can we pass values into methods and get values out of methods?
• Parameters are the list of values as comma deliniated variables we can pass into the method. We can have as many parameters (inputs) as we want. Although it is true that these variables are defined locally ( i.e. within a method ) the values they get are equal to the values the calling function supplies in it argument list. The order of the list determines which values are assigned to which varaibles. For example, the method myMethod( int a, int b, float c ) has three parameters, the first two are integers and the last one is a float. If I were to pass it the values 1 , 2, and 7.1234 to the method like this myMethod( 1, 2, 7.1234 ) then a would get the value 1, b would get the value 2, and c would get the value 7.1234. Order determines which value is assigned to which varaible.
• Method call ( function call ) - when I try to run a method I simply write the name of the method followed by ( ). inside the ( ) I place the list of parameters I want to pass to the method. This is called a method call.
• Return values - If a method outputs some value when it is done, this is called a return value. To return a value, use the key-word return followed by the value you wish to return. This statement occurs inside the method and causes the method to exit immediately. The return value is sent back to the place where the method was called. If there was an assignment operator there for example, the variable being assigned will get the value the method returns.
  For example: int a = myMethod( 1, 2, 7.1234) .
  a will be assigned the value myMethod returns. Methods can return only one value. You must specify the type value the method returns, for example int or float or String.
• Method definition - Writing the method is called defining it. Some methods are built-in, but the programmer may write his own methods. To do this, he must define the method. That is, he must define what return value type he intends to return, what paramenters he can accept, and of course what the method will actually do with the values it receives when it is called.
  Here is a method definition:
  
  float myMethod ( int a , int b , int c, float d)
  {
  return ( ( float )a * ( float )b * ( float )c / d );
  }
• Method overloading (not on midterm)

       
© Nachum Danzig November 2003