The Unified Modeling Language

• use case diagram
• class diagram
• behavior diagrams:
  • statechart diagram
  • activity diagram
  • interaction diagrams:
    • sequence diagram
    • collaboration diagram
• implementation diagrams:
  • component diagram
  • deployment diagram

Design by Contract

• formal basis -- pre and post conditions
• refinement -- by inheritance or polymorphis
• runtime checks -- division of responsibility

Frameworks = Components + Patterns

Ralph Johnson, CACM Nov. 1997

Self-documentation Principle

Bertrand Meyer, OO Software Construction 2nd ed.

the designer of a module should strive to make all information about the module part of the module itself ...

A Catalogue of Design patterns

• a common design vocabulary
• documentation and learning aid
• an adjunct to existing methods
• a target for redesign

structure

Name - handle

• increases design vocabulary

Problem - when to apply

• explains the problem and the conflict

Solution - general arrangement

• design, responsibilities, collaborations

Consequences - tradeoffs

• to understand the costs and benefits

Causes for Redesign

design for change

1. creating an object by specifying a class explicitly -- Abstract Factory, Factory Method, Prototype
2. dependence on specific operations Chain of Responsibilty, Command
3. dependence on hardware & software platforms -- Abstract Factory, bridge
4. dependence on object implementation or representation Abstract Factory, Bridge, Memento, Proxy
5. algorithm dependence -- Builder, Iterator, Strategy, Template Method, Visitor
6. extending functionality by subclassing -- Bridge, Chain, Composite, Decorator, Observer
7. tight coupling -- Abstract Factpry, Bridge, Chain of Responsibilities, Command, Facade, Mediator, Observer
8. inability to alter classes conveniently -- Adaptor, Decorator, Visitor

Kinds of Patterns

• creational patterns -- factory, singleton, ...
• structural patterns -- adaptor, composite, bridge, ...
• behavioral patterns -- mediator, observer, command, ...

see also

see Ted Lewis, IEEE Computer, March 1997, p. 136

The dream: UNCOL

• Java is pervasive
• remember, most of Java is just warmed-up C/C++

UNCOL = Universal Common Language

• (1963) Algol -> PL/I -> Pascal -> Ada -> C++ -> ...
• Java as UNCOL: the dial-tone of the Internet

if todays languages are inadequate for Software then Java must be inadequate too ...

Hostages of legacy code

• our responsibility is that future applications (built with Java) are well-behaved legacy systems
• US DOD: $30\; billion\; in\; year\; 2000\; problem$
• maintaining legacy COBOL from the 70's is a major industry ...
• by 2010, Java will be the maintenance tail wagging the software dog!

Is Java doomed to repeat history?

• elegant minimalism is one of the goals of Java,
  remember Pascal, a toy language!
• Java lacks IO, OS support ...

Problems

• syntax: int i = ++i--;
• unruly scope rules: C++ plus f i n a l, n a t i v e, s y n c h r o n i z e d, ...
• threads: potential deadlocks

Java: a better mousetrap?

• requirements: no support (assert)
• defacts: syntax, non-standard APIs
• components: Beans <-> ActiveX, CORBA, OpenDoc
• cycle time: Java does little to accommodate Internet time, like script languages do
• complexity: Java does not advance the intellectual frontier!

CORBA

• the issue is standardization
• by means of interfaces
• looking for consensus
• this differs from a de-facto standard
• imposed by market share ...

Dimensions of Risks

• Knowledge
• Teaming
• Productivity
• Ownership
• Distractions

knowledge

• clear the fog -- get to the real issues
• early and regular delivery -- discover what you don't know
• prototype! -- discover how it really works
• create microcosm -- do something real, but with care

teaming

• holistic diversity -- coordinate specialists!

productivity

• gold rush -- start immediatly, adjust slowly

ownership

• function / component owners -- create responsibility

distraction

• someone always makes progress -- no total interruption
• team per task -- a subteam deals with diversions
• sacrifice one person -- and preserve the team

training

• day care -- hire an expert to take care of novices