Using Java Objects

1
Using Java Objects

• Using Objects
• Mixing objects and data types
• Purpose of the toString method
• Robert Stumpf, Ph.D.
• CIS Department

2
Using Objects

• Messages are usually sent to variables
• Variables point to objects
• Messages invoke a method in objects class
• Messages may have arguments
• Messages may also be sent to classes directly
• Methods may return a response

3
Using Objects

• Example messages without arguments sent to
  variables
• With no response
• window.show ( )
• With a response.
• inputLine fileIn.readLine ( )

4
Using Objects

• Example messages with arguments sent to variables
  
• With no response
• window.reshape (0, 0, 600, 400)
• With a response.
• value dictionary.get (key)

5
Using Objects

• Example messages without arguments sent to
  classes
• With no response
• no examples, why ?
• With a response.
• numberFormat NumberFormat.getCurrencyIns
  tance ( )

6
Using Objects

• Example messages with arguments sent to classes
• With no response
• System.exit (0)
• With a response
• anInteger Integer.parseInt (aString)

7
Mixing Objects and Data Types

• Message arguments may be objects or data types
• Using an object anInteger Integer.parseInt
  (aString)
• Using a data type window.reshape (0, 0, 600,
  400)

8
Mixing Objects and Data Types

• Message responses may be objects or data types
• Receiving an object todaysDate Date ( )
• Receiving a data type anInteger
  Integer.parseInt (aString)

9
Mixing Objects and Data Types

• Mathematical functions are available using the
  class methods from Math class
• For example
• Math.pow (1.06, 2.0) yields 1.1236
• Math.sqrt (9.0) yields 3.0
• Math.round (1.5) yields 2L

10
toString

• All Java objects understand the message toString
  ( )
• This assures the programmer can always convert
  whatever object they wish to a printable form
• For example
• String string
• string temperature.toString ( )

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toString

• This means all programmers must construct their
  own classes with a toString method
• If a programmer forgets to do this, their object
  will use the parents object (usually Object)
  toString method
• This will usually lead yield a cryptic output
• For an example of a cryptic output, see
  GregorianCalendar

12
Summary of Objects

• The receiver of the message is always on the left
• A dot is always is always used to separate a
  message from a class or object
• The receiver is always a class or a variable
  pointing to an object
• The message may have arguments
• The method may return a response

13
Thank You

• There are no speed limits
• on the road to excellence.Thank you
• Robert Stumpf
• email rvstumpf_at_csupomona.edu
• url http//www.csupomona.edu/rvstumpf