Copyright © 1997-2014
Robert W. Hasker

Review: Java from bottom up

• simple statements: input, output, assignment
  • System.out.println, in.next() are actually ____ calls!
• control:
  • selection (if, switch)
  • repetition (while, for, do-while)
  • grouping (compound statement)
• variable declarations
  • can initialize variable at same time
  • variables must be made up of letters, digits, and underscores
    • don't start with digit
    • don't use a reserved word (like float or while)
• types
  • simple types:
    • (scalar:) int, char, boolean
    • measures: float, double
  • arrays: collection of items each with same type
    • Note: type can be an array: int [][] grid;
  • classes
    • attributes, methods, constructor, static final data
• expressions:
  • precedences (can override with parens):
    • high:
    • [] . () ++ -- (where ++, -- are post-increment)
    • ++ -- ! unary + - (where ++, -- are pre-increment)
    • * / %
    • + -
    • < <= > >=
    • == !=
    • &&
    • ||
    • low: = += -= etc.
  • type rules:
    • combining float and int: result is float
    • / with floats is different than / with ints
• methods, parameters
  • arguments vs. parameters
  • simple types: pass the value
  • instances of classes: pass the reference
  • Scope, lifetime
• Reading data
  • Scanner input = new Scanner(System.in); - read from console
  • input.next() - read next word, skipping any whitespace
  • input.nextLine - read next line; used rarely
  • input.nextInt(), input.nextDouble - read next integer/double
  • JOPtionPane.showMessageDialog(null, "message")
  • JOptionPane.showInputDialog("prompt") - returns input as string

Building Software Systems

• This class: writing Java programs.
  • There's more to developing applications than this, though!
• Steps:
  1. business decision: will building application be worth the cost
     • is management committed?
     • is there a social impact?
  2. requirements: what does customer need?
  3. analysis: more detailed requirements, deciding what pieces to implement in hardware vs. software
  4. design: breaking system into components, decide on algorithms and software architectures
  5. implementation: translating design into C++
  6. testing: verifying system does what customer wants/needs
• Writing code less than 25% of project!
  • determining what customer wants/needs: much domain-specific knowledge
  • managerial activities: coordinating efforts, negotiating schedules
  • verifying system meets customer needs and expectations

Another theme: problem solving

• First step: ask questions: make sure you know what the problem is!
  • know inputs, outputs
  • know how much data you need to deal with
  • what are the errors that we must address?
• Second step: find solution
  • look for similar problems you've already solved
    • maybe the new problem is similar with different names
    • maybe the new problem contains components that you've solved elsewhere
  • means-ends analysis: identify intermediate goals, figure out how to get from one goal to the next
  • divide and conquer: break large pieces into smaller pieces
• Biggest problem: mental blocks
  • solution: start by writing down what you do know

Sample Real-world Projects

• Cellular Phone Billing System
  • typical business application (computer information systems emphasis)
  • process call records, calculate charl. various taxes), print bills, track payments, track customer issues
  • front-end: GUI to handle customer calls/requests
  • back-end: reports on system (eg: commission payments); interfaces to telephone switch and bank; past-due notices
  • big issue: converting data from one system to another when a new cell-phone agency installs a new billing system
  • approximately 1/2 million lines of code
• Flight Management Controller
  • controller for in-flight fueling jet
  • controller: responsible for ensuring jets don't crash; handle take-off and landing with an extremely dangerous load; autopilot for very long missions
  • basic architecture: interface with a dozen subsystems; give pilot control through touch-panel; control flight path; distribute fuel; advise pilot of emergencies
• future:
  • when your clothing contains a computer, computation needs will make today look like the stone ages!
  • computers will be so tiny they can be sprayed on your wall with paint!
    • application: emit sound to cancel out noises on the other side of the wall

Professional Responsibility

• We've discussed how to write a program, but not much about what programs should be written!
  • Programmer has responsibility to not make the world a more dangerous place with his or her program.
    • Programmer must ensure he or she has the necessary skills!
    • Programmer must also often be the conscience.
• Examples:
  • programs which use SSN as id numbers
    • SSN is not a password
  • transmitting patient records from Dubuque to Madison
    • Can they be intercepted? spoofed?
  • more controversial: traffic cameras at intersections
    • Computers continue to double in power about every year and a half
    • At some point, there will be enough computational power to build computers that can track everything - is this good?
• Too many people look at the computer as the ultimate solution without asking the cost; programmer must ask serious questions before agreeing to build the system.