Modules (Methods)

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Modules (Methods)

• Functions and Procedures
• Parameters ...Output

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Procedures and Functions

• Some of our pseudocode rules translate into firm
  rules in Java
• Functions return a single value
• Value returned can be any complex data type
  (including an Object)
• Procedures can return information by changing
  an object that is passed in via a parameter.
• Other rules are style issues
• Functions having no side effects
• Functions not doing I/O

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Java Methods

• Single construct for both procedures and
  functions
• When a function is called for, specify the
  appropriate return type before the method name
• public float average (float fNum1, float
  fNum2)
• float fReturnVal
• fReturnVal (fNum1 fNum2)/ 2
• return fReturnVal
• // of average
• to specify a procedure, make the return type void
  
• (More later)

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Writing Methods
A Java requirement --All methods belong to an
object (or class). --Name of object (or class)
must be unambiguous when the method
called. --To run a program, there must be a
class (whose name is the name-of-the-program),
containing a special method called main
for command line parameters
visible to all
nothingreturned
public static void main (String argv)
a class method,not aninstancemethod
Method name
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Method Overloading

• Sometimes more than one method is required to do
  the same job.
• In Pseudocode, we frequently used a helper module
• Procedure Convert(Lhead iot in Ptr toa
  LLNode)
• Procedure ConvertHelper(Lhead iot Ptr toa
  LLNode,
• NewHead iot Ptr toa
  LLNode)
• In Java, multiple methods can have the same name
  as long as the number, type or order of their
  parameters is different
• public void Convert(LLNode Lhead)
• public void Convert(LLNode Lhead, LLNode
  NewHead)

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Method Signatures

• The signature of a method consists of the name
  of the method and the number and types of formal
  parameters to the method. A class may not declare
  two methods with the same signature, or a compile
  time error occurs.
• Java Language Specification s.8.4.2
• Method overloading occurs where identically named
  methods have different parameter (number, type or
  order NOT name!)
• public int getCube(int iNum)
• return iNum iNum iNum
• public int getCube(float fNum)
• return (int)(fNum fNum fNum)
• public int getCube(double dNum)
• return (int) (dNum dNum dNum)

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Methods Common Mistakes
public float average (float fNum1, float fNum2,
float fNum3) float fReturnVal
fReturnVal (fNum1
fNum2 fNum3)/ 3 return (fReturnVal)
// of average
Note ending semicolon -- results in unhelpful
error message
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Parameters

• Java only has in parameters
• Initially this will appear to be a big change. It
  is a common feature in many languages.
• We can get information out of a module via two
  techniques
• Return something from a function
• Pass in a reference to some object and inside the
  method modify the object side effect

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Printing to Screen

• Pseudocode
• print (ltargumentsgt)
• Java
• System.out.print(ltA Stringgt)
• System.out.println(ltA Stringgt)

Inserts a newline after the printing is complete
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Printing to Screen

• int x 10
• System.out.println(5)
• System.out.println( )
• System.out.println(Hello World)
• System.out.println(x x)
• System.out.println(y 5)
• System.out.print(All on one )
• System.out.println(line)

5 Hello World x 10 y 5 All on one line
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