Application Programming

1
Application Programming

• From the operating systems perspective,
  everything that is not the OS is application.
• From the programmers perspective, there are a
  number of components that function as
  infrastructure effectively extensions of the
  OS...
• Editors
• Compilers
• Database Management Systems
• Everything (including the OS) has to be written
  in some language

2
Programming Language Concepts

• A programming language is a restricted form of
  expression with a concise grammar and an
  unambiguous semantics
• The full grammar can be printed on a few pages
• Pascal 2
• Java 13
• Ada 16

3
Programming Language Concepts

• A grammar sample for integers and real numbers
• ltdigitgt 0 1 2 3 4 5
  6 7 8 9
• ltdig seqgt ltdigitgt ltdigitgt ltdig seqgt
• ltintegergt ltdig seqgt
• ltreal numbergt ltdig seqgt . ltdig seqgt

4
Programming Language Concepts

• The semantics explains the meaning of the
  language constructs
• Pascal 32 pages
• Java 423 pages
• Most of the verbage involves explaining in
  English something that take only a few lines
  using formal techniques (denotational semantics)

5
Language Scope Coverage

• Computational Model
• A metaphor shielding the specific machine details
• Data Types and Operations
• Structure and manipulation of values
• Simple characters, integers, etc.
• Complex arrays, records, lists, etc.

6
Language Scope Coverage

• Abstraction Facilities
• Formation of larger scale units from smaller
  units
• Procedures, functions, etc.
• Classes, packages, etc.

7
Language Scope Coverage

• Checking Enforcement
• Compile-time
• Missing syntax (grammar)
• Variable mismatches (semantics)
• Run-time
• Divide-by-Zero
• Uninitialized variables

8
Language Levels

• Machine Language
• Directly executable by the CPU
• 00000010101111001010
• 00000010111111001000
• 00000011001110101000
• Clusters of bits are routed to the control unit,
  arithmetic unit, etc.

9
Language Levels

• Assembly Language
• A symbolic variant of machine language
• LOAD I
• ADD J
• STORE K
• Various segments of bit patterns are replaced
  with symbols
• 00000010 -gt LOAD
• 00000011 -gt STORE

10
Language Levels

• High(er) Level Languages
• Emphasis on the abstraction of the computation
  (the metaphor), rather than the machine
• K I J
• Significant translation requirements, supported
  by a compiler or interpreter

11
Commmon Languages

• FORTRAN
• Numerical calculation, little or no support for
  text, graphics
• COBOL
• Business data processing
• Repetitive calculation over large amounts of data

12
Commmon Languages

• C
• Low/high level language originally designed for
  systems programming
• Support for address arithmetic
• Java
• Object-oriented language closely tied to a
  virtual machine definition, allowing execution of
  the same program on many machines
• Direct support for threads multiple execution
  points in a single program

13
Programs and Models

• A model is a simplified representation, focussing
  on some features and neglecting others
• Rarely complete
• Dissimilar from that it represents in some manner
• Can represent imaginary or hypothetical concepts

14
Model Characteristics

• Elements represent external, frequently more
  complex things
• Elements exhibit consistent behavior
• Elements can be grouped into different categories
  based upon common behavior
• Actions external to a model element cause
  behavior of that model element

15
Java Lingo (really Object Lingo)

• Objects model elements in Java programs
• Classes Objects sharing common behavior
• Instance (of a class) an object belonging to
  that class
• Reference any phrase that is used to refer to an
  object
• Message a request for some desired behavior from
  an object
• Method the definition (within a class) of some
  form of behavior

16
The Bottom Line...

• Programming in Java amounts to nothing more or
  less than writing the definitions of classes and
  using those classes to create objects.

17
The Application Life Cycle