chapter 4
is-a relationship
the relationship between an object and the class of which it is a member.
class client
an application or class that instantiates objects of another class. See also class user.
class user
an application or class that instantiates objects of another prewritten class. See also class client.
extended
describes classes that have descended from another class.
data fields
data variables declared in a class outside of any method.
instance variable
a nonstatic class field that exists separately for each instantiated object.
private access
describes a field or method that no other classes can access.
information hiding
the object-oriented programming principle used when creating private access for data fields that describes that a class’s private data can be changed or manipulated only by a class’s own methods.
mutator methods
methods that set field values.
accessor methods
methods that return information about an object.
Nonstatic methods
methods used with object instantiations. See also instance methods.
instance methods
methods used with object instantiations. See also nonstatic methods.
primary key
a unique identifier for data within a database.
new operator
an operator that allocates the memory needed to hold an object.
reference to an object
a memory address where an object is held.
constructor
a method that establishes an object.
abstract data type (ADT)
a type whose implementation is hidden and accessed through its public methods.
programmer-defined data type
a type that is created by a programmer and not built into the language; a class.
default constructor
a constructor that requires no arguments.
this reference
a reference to an object that is passed to any object’s nonstatic class method.
override
describes the precedence of a variable’s name in a called method when the same name exists in the calling method; also to use the child class’s version of a field or method instead of the parent’s.
shadowing
the action that occurs when a local variable hides a variable with the same name that is further away in scope.
closer in scope
a term that describes the status of a local variable over others that it shadows.
class methods
static methods that do not have a this reference (because they have no object associated with them).
class variables
static variables that are shared by every instantiation of a class.
NaN
abbreviation for Not a Number.
library of classes
a folder that provides a convenient grouping for classes. See also package.
java.lang package
the package that is implicitly imported into every Java program and that contains the fundamental classes.
fundamental classes
asic classes contained in the java.lang package that are imported automatically into every program. Contrast with optional classes.
optional classes
classes that reside in packages that must be explicitly imported into programs. Contrast with fundamental classes.
wildcard symbol
a symbol used to indicate that it can be replaced by any set of characters. In a Java import statement, the wildcard symbol is an asterisk ( * ).
enumeration
a data type that consists of a list of values.
nanosecond
one-billionth of a second.
Composition
describes the relationship between classes when one class object is a data field in another class. Also, sometimes more specifically, a containment relationship between classes when an object of the contained class would cease to exist without the containing class. See also has-a relationship.
has-a relationship
a relationship based on containment.
nested classes
classes contained in other classes.
top-level class
the containing class in nested classes.
static member classes
nested classes that have access to all static methods of their top-level class.
Nonstatic member classes
nested classes that require an instance. See also inner classes.
inner classes
nested classes that require an instance. See also nonstatic member classes.
Local classes
nested classes that are local to a block of code.
Anonymous classes
Anonymous classes