Barron's: AP Computer Science A: Chapter 3: Classes and Objects
actual parameters
(aka arguments) parameters supplied by method calls in a client program
static method
(aka class method) performs an operator for the whole class → cannot call instance variates or methods since there is no class → used to manipulate static variables → invoked with the class name with the dot operator
null pointer
(aka null reference) an uninitialized object variable → can test if variables are null or set them to null → trying to use, will produce a NullPointerException
reference data type
Strong, Random, int[], etc. refer to the address in memory where an object is stored
explicit parameter
a parameter of a method other than the object on which the method is invoked; parameters passed in the parameter list
class
a software blueprint for implementing objects of a given type
object
a thing created and manipulated by a program; it corresponds to some real world object that is being represented by the program → has a state and behaviors → an instance of a class
method headers
access specifier return type method name parameter list
accessor method
accesses a class object without altering the object; returns some information about the object
this
as a parameter, will call the implicit parameter with a dot operator, can be used to call instance variables instead of explicit parameters with the same name
mutator method
changes the state of an object by modifying at least one of its instance variables
encapsulation
combining an object's data and method into a single unit (a class)
fail to initialize local variables
compile-time error
driver program
contains a <<main( )>> method used to test programs → all methods in the class including <<main( )>> must be static
static variable
contains a value (that can be changed) that is shared by all instances of the class; indicates that there is a single value of the variable that applies to the whole class, rather than a new instance for each object of the class → keep track of statistics for objects of the class → accumulate a total → provide a new identity number for each new object of the class
static final variables
contains a value (that cannot be changed) that is shared by all instances of the class
constructor
creates an object of the class → same name as the class → no return type
state
decided by data fields (aka instance variables)
primitive data types
double, int, char, boolean, etc. each has its own memory slot that stores the actual value
default constructor
has no arguments; provides reasonable initial values for an object
aliasing
having multiple references to the same object
dot operator
indicates that a method is in a certain class of an object
___ take precedence over ___ with the same name
local variables take precedence over instance variables with the same name
public methods
methods accessible to all client programs
instance methods
operate on individual objects of a class
passing primitive types as parameters
parameters are passed by value so *any changes made to the parameter will not affect the values of the arguments in the calling program* since a new memory slot is created for each parameter
formal parameters
placeholders for values in the method signature
object reference
representing an object as a variable store the addresses of their respective objects *NOT* the objects themselves
data hiding
restriction of access of data → using the key word <<private>>
new
returns the address of this newly constructed object
public
signals that the class is usable by all client programs
void
signals the method does not return a value
passing objects as parameters
the address (reference) is copied into memory, so although the method cannot replace the object, it can change the object's state → use the assignment operator and a method that returns an address to replace an object
fail to initialize instance variables
the compiler produces reasonable default values (0, 0.0, false, or null)
method signature
the method's name and a list of the parameter types
implicit parameter
the object of a method
scope
the region in which that variable or method is visible and can be accessed → instance and static variables and methods' scope is the entire class → local variables' scope is the method (or block) they are in
overloading methods
two or more methods in the same class that have the same name but different parameter lists → dependent on the method signature → the return type of the method is irrelevant so you cannot have two methods with the same signature but different return types → having more than one constructor
