UNIVERSITY AT BUFFALO, THE STATE UNIVERSITY OF NEW YORK
The Department of Computer Science & Engineering

STUART C. SHAPIRO: CSE 115 C

Reading

Brown U. Notes, Chapter 3

Barnes, Chapters 3, 4

Variables

Variables include static (or class) variables, instance variables, local (or method) variables, and formal parameters.

A variable has a name, a type, and a value.

The compiler will check that the value given to a variable is compatible with the variable's declared type.

Java-speak uses the terms "message" and "method" to refer to the same thing---a capability or behavior of an object.
Can say one object sends a message to another, which the latter understands, or that one object calls another's method.

Define a method, specifying its list of formal parameters (or arguments), with their types.

Call a method with one actual parameter (argument) for each formal parameter, agreeing as to type. The compiler will check.

A method may return a value.
So a method must have a type---the type of the value it will return,
or void if it doesn't return a value, just does something.

Some common methods:

Constructor

Creates a new instance of the class.
public Class(formal parameters){...}

Accessor

Returns the value of an instance variable or a class variable.
public Type getVariable(){...}

Mutator

Changes the value of an instance variable or a class variable.
public void setVariable(formal parameters){...}

Main

Starting point of an application.
public static void main (String[] args) {...}

Scope and Lifetime

Scope is the spatial extent of the source code where a variable can be referred to by its name.

Lifetime is the temporal extent in the run of the program during which a variable retains the last value it was assigned.

Scope:

Class and instance variables

Scope is the entire class definition (the block in which they are declared). But a static (class) method cannot refer to an instance variable.

Method variables

Scope is from the point they are declared through the block in which they are declared. For the method variables we've seen so far, this is the entire rest of the method body.

Formal parameters

Scope is the body of the method for which they are formal parameters.

Lifetime:

Class and instance variables

Lifetime is the entire run of the program (as long as any variable contains a reference to the instance or any instance of the class).

Method variables

Lifetime is while the method is executing.

Formal parameters

Lifetime is while the method is executing.

We will look at the ParameterDemo package containing the classes StringHolder and ParameterTest.
Note the documentation created by javadoc from the comments.

Stuart C. Shapiro <shapiro@cse.buffalo.edu>