Review of Terms and Concepts from Last Semester

Variables/Constants/Literals

Variable

A named space for holding values. Its name is referred to as its identifier.

Atomic Variable

A variable that can hold one datum (e.g., a number or a character).

Complex Variable

A variable that can hold multiple data (e.g., a class or an array).

Data Type

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

Primitive Data Type

A data type that is predefined in a programming language.

Constant

A named space for holding values. The value may not change once initialized.

Literal

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

Variables and constants must be predefined to be used in a Java program.

By convention, we declare variables and constants at the beginning of the method (or function) in which they are used. Prefer no initialization with declarations.

By convention, declarations should be grouped based on data type.

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

For 239, if your variable names are CLEAR you don't need to document each one. You MUST use the @param for input arguments and each of these 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 a result.

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, pg 74 for further discussion of data types.

Operators

Operator

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

Operand

A variable, literal, constant, or an expression.

Binary Operator

An operator that takes two operands.

Unary Operator

An operator that takes a single operand.

Operators

Memorize the truth tables

Operator precedence * / before + - and && before ||

Automatic data conversion - Done as it is needed, operation by operation. Wrapper class - autoboxing

Type casting - Done at whatever point you want to change the type.
Casting is in the precedence rule list.

Examples: Operator.java

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

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

For 239, 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

Two decision (or selection) statements in Java, if and switch.

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 239 reference for: Jam 8, 2008 JMU CS 239