Outline

One of the goals of this course

Dr. Arch Harris's Programming Style Guidelines

Review of Terms and Concepts from Last Semester

Variables/Constants/Literals

Identifier

Any name in Java.  Classes, variables, constants, methods all have identifiers.

Variable

A named space for holding values. Its name is called its identifier.  The values of a variable can change during program execution.

Constant

A named space for holding values. The value may not change once initialized. (By convention, initialize all constants at declaration.)

Literal

A value used explicitly in a program, such as the number 1 or the String "abc".

Data Type

A designation that specifies a set of values (which may be infinite).

Variables and constants must be predefined to be used in a Java program.  By convention, we declare all variables and constants at the beginning of the class or method in which they are used.Exception is a for loop when the variable is strictly used as a loop control variable.

Self documenting code suggests that variable names should make intuitive sense and should be used for only one purpose in any program.  

You MUST use the @param for each input argument and they must be documented individually, one per line.

Java will not allow automatic narrowing conversions (loss of precision message) (except when ????) Use type-casting to explicitly change the type of an expression.

Examples: Variable.java

Note: All data is stored in binary on the computer. That limits the range of values for each of the primitive types. See book, Chapter 2 for further discussion of data types.

Operators

Operator

A symbol indicating that an operation is to be performed on one or more operands.  

Operand

The value(s) that an operator works on.  An operand may be a literal, constant, variable, or an expression.

Binary Operator

An operator that takes two operands.

Unary Operator

An operator that takes a single operand.

Tertiary Operator 

The conditional operator takes 3 operands.  See chapter 3.8 if you are interested.

Operators

Memorize the truth tables

Operator precedence - Always use parentheses to resolve precedence.  

Automatic data conversion - Done as it is needed, operation by operation. Java will automatically perform widening conversions, but not narrowing conversions**.  Wrapper class - "autoboxing".

** - See combined operators

Type casting - Done at whatever point you want to change the type of the value. Does not change the type of the variable.

Examples: Operator.java

DeMorgan's Laws: ! (a && b) is equivalent to !a || !b

and ! (a || b) > is equivalent to !a && !b

For 159, you may use mixed operators (+=) as long as you know exactly what they can do (and a nasty side effect if you are not careful).

Decisions

There are two decision (or selection) statements in Java, if and switch and one conditional operator.

if (condition)
       statement (or statement block)
else
       statement (or statement block)

Alternate format:

if (condition) statement;
else statement;

Examples: Decisions.java

Loops

Four items to look for in a loop structure:

• initialization or setup
• decision (condition for continuing)
• body (or actions)
• update

Types of loops

• pre-condition loop - while
• post-condition loop - do/while
• counted loop (special form of pre-condition loop) - for

Terms

Termination/Exit Condition:

The condition which when false will cause the loop to terminate.

Sentinel or Sentinel Value:

A specific value which signals that the loop should terminate. Not a normally processed value.

Infinite Loop:

A loop whose termination condition is never reached. The loop will not naturally end.

Off by one Error:

A loop that executes one too many or one too few times.

Indefinite Loop:

A loop that terminates when a termination condition is reached where the number of iterations is not known ahead of time.

Loop usage

• Accumulators
• Creating a list
• Validate input
• Searching and sorting
• Prompt for multiple values
• Simulate processes through time
• Move through lists

Loop equivalency - A loop may be rewritten (sometimes awkwardly) as any other kind of loop.

See example: Loops.java

JMU CS 159 reference for: Jan 13, 2013 JMU CS 159