writing and calling methods

1
writing and calling methods
2

• package CSE115MethodExamples
• public class MathClass
• public MathClass( ) // empty
  constructor
• public void add( int A, int B)
• int C
• C A B
• System.out.println( C )
• // end Add
• public void multiply( int A, int B)
• int C
• C A B
• System.out.println( C )
• // end Multiply
• // end class MathClass

MathClass is a very useful class, but what does
"void" mean?
3

• package CSE115MethodExamples
• public class MathUser
• public MathUser( )
• MathClass calc new MathClass( )
• calc.add (10, 4 )
• calc.multiply( 1200, 167 )

• package CSE115MethodExamples
• public class Starter
• public static void main(String args )
• MathUser app new MathUser( )

Starter "uses" MathUser
MathUser "has a" MathClass
4
a deficiency

• MathClass.add and MathClass.multiply ONLY PRINT
  TO THE SCREEN
• What if you need the results in MathUser?

5

• package CSE115MethodExamples
• public class MathClass
• public MathClass( ) // no constructor
• public int add( int A, int B)
• int C
• C A B
• return( C )
• // end Add
• public int multiply( int A, int B)
• int C
• C A B
• return( C )
• // end Multiply
• // end class MathClass

replace the "prints" with "returns"
6

• package CSE115MethodExamples
• public class MathUser
• public MathUser( )
• int x, y
• MathClass calc new Mathclass( )
• x calc.add (10, 4 )
• y calc.multiply( 1200, 167 )
• System.out.println( x " " y )

7
MathClass "specification"

• package CSE115MethodExamples
• public interface IMathClass
• public int add( int A, int B)
• public int multiply( int A, int B)
• // end interface IMathClass

Why?
8
why specify an interface? especially if the class
already works?

• So that in the future, other programmers can
  produce a better MathClass that works the same
  way
• It is a way of advertising what the MathClass does

9
final MathClass

• package CSE115MethodExamples
• public class MathClass implements IMathClass
• public MathClass( ) // no constructor
• public int add( int A, int B)
• int C
• C A B
• return( C )
• // end Add
• public int multiply( int A, int B)
• int C
• C A B
• return( C )
• // end Multiply
• // end class MathClass

10
MathUser
Starter
IMathClass
uses
has a
implements, or realizes
MathClass calc new Mathclass( )
public Starter( ) new MathUser( )
MathClass
public class MathClass implements IMathClass
11
MathClass
MathClass
C

• C MathClass( )
• int add( int A, int B)
• int multiply( int A, int B )

12
IMathClass
MathClass
I

• int add( int A, int B)
• int multiply( int A, int B )