Java Programmers Certification - Glossary

Absolute value

The absolute value of a negative number is the number multiplied by -1. The absolute value of a non-negative number is the same as the number.

Abstract method

A method whose implementation is deferred to a subclass.

Access modifier

A modifier that is used to limit access to a class, class member, or constructor.

Automatic variable

A variable whose scope is limited to a code block within a method. Automatic variables are also referred to as local variables.

Blocking on I/O

Waiting for an I/O operation to be completed.

Cast

To convert from one type to another.

Catch or declare rule

If an exception can be thrown during the execution of a method then the method must either catch the exception or declare it in the method's throws clause.

Class

A template for the creation of objects.

Classification

The organization of information into hierarchical categories.

Clipping

Painting to an area that is restricted by a geometric shape, usually a rectangle.

Compilation unit

A source code file.

Component

A GUI element.

Constant

A variable whose value is final and cannot be changed.

Constructor

A special method that is used to create objects as instances of a class.

Container

A component that is used to collect, organize, and display other components.

Context Switching

When a CPU switches from executing one thread to executing another, the CPU needs to save the local data and program pointer of the current thread, and load the local data and program pointer of the next thread to execute. This switch is known as a context switch. The CPU switches from executing in the context of one thread to executing in the context of another thread. Context switching requires resources and you do not want to switch between threads more than is necessary.

Current object instance

The current object that is being executed.

Degree

A unit of angular measurement.

Deprecated

In the process of being removed from the Java language or API.

Deserialization

Reading an object from a stream.

Dimensions

The size of an array.

Direct or random access I/O

I/O that is performed to or from direct locations of a file.

Direct superclass

The class that is identified in a class's extends clause. If a class is declared without an extends clause, then its direct superclass is java.lang.Object.

Dynamic binding

A program compilation and execution feature that allows programs to delay until Runtime decisions about the type of objects that they access.

Eligible for garbage collection

An object that is unreachable is eligible to be destroyed and have its resources reclaimed by the garbage collector.

Encapsulation

A quality of classes with well-defined and controlled interfaces.

Enclosing scope

The instance of an outer class in which an instance of an inner class is created.

Enclosing statement

A statement, such as a switch, if, or loop statement, that contains the statement block of the statement in question.

Entry point

The first method that is executed when an application (main()), thread (run()), or applet (init()) is executed.

Event

An object that signals the occurrence of an action.

Event adapter

A class that provides a default implementation of an event listener interface.

Event bubbling

Event bubbling describes the JDK 1.02 event-handling approach. Events are handled by subclassing a component and overriding its event handling methods. Unhandled events are propogated to a component's container. Event bubbling is also referred to as event inheritance.

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Event delegation

Event delegation describes the JDK 1.1 event-handling approach. Event listeners are registered with the source of an event. When an event occurs, the source invokes the event handling functions of its event handlers.

Event inheritance

Event inheritance describes the JDK 1.02 event-handling approach. Events are handled by subclassing a component and overriding its event handling methods. Unhandled events are propogated to a component's container. Event inheritance is also referred to as event bubbling.

Event listener

An object that registers itself to handle the occurrence of an event.

Exception

An object that signals that an abnormal event or error has occurred.

Execution state

The states occupied by a thread during the course of its execution.

Field

Short for field variable.

Field variable

A variable that is a member of a class.

File pointer

A pointer to a location within a file.

Filter

An object that reads one stream, performs an operation on the data that is read, and writes it back out as another stream.

Friendly access

The default access that occurs when no access modifier is specified. Access is restricted to the package in which an item is declared. Also referred to as package access.

Garbage collection

The process by which the memory occupied by unreachable objects is reclaimed.

Hash table

A table which maps elements to their values based upon a hashing algorithm. A hashing algorithm provides a uniform distribution of values over a certain range.

IEEE 754 standard

The IEEE 754 standard is standard for implementing floating-point numbers and floating-point arithmetic.

If condition

The condition that is evaluated as part of an if statement.

Inheritance

The passing on of design information from a superclass to a subclass.

Initializer

A block of code that is used to initialize a variable.

Inner interface

An interface that is declared as a member of another class or interface.

Interface

Using interface, you can specify a set of methods that can be implemented by one or more classes. In its traditional form, the interface, itself, does not actually define any implementation.

Java Web Start

Java Web Start is a framework developed by Sun Microsystems which allows application software for the Java Platform to be started directly from the Internet using a web browser. Unlike Java applets, Web Start applications do not run inside the browser, and the sandbox in which they run does not have to be as restricted, although this can be configured. One chief advantage of Web Start over applets is that they overcome many compatibility problems with the different Java browser plugins and different JVM versions. On the other hand, Web Start programs cannot communicate with the browser as easily as applets. To assist migration, a Java Applet can also be used as a Java Web Start application.

Last-in first-out stack

A data structure in which the last element added is the first element retrieved.

Layout manager

An object that is used to organize the way in which components are displayed as part of their container.

Layout policy

The policy used by a layout manager to lay out a container.

Left associative

Operations that are left associative are performed in a left to right manner. That is, x op y op z is evaluated as (x op y) op z.

Local inner class

An inner class that is declared local to a block of code.

Local variable

A variable whose scope is limited to a code block within a method. Local variables are also referred to as automatic variables.

Lock

A mechanism for implementing shared access to an object. Also referred to as a monitor.

Member

An element of a class or interface, such as a field variable, method, or inner class. An element of a package, such as a class, interface, or subpackage.

Member variable

Another name for a field variable.

Method

A member of a class that allows operations to be performed on objects of that class.

Method signature

The name of the method and the number and types of formal parameters to the method.

Modifier

A keyword that is used to modify the definition of a class, variable, method, or constructor.

Monitor

A mechanism for implementing shared access to an object. Also referred to as a lock.

Multiple inheritance

The inheritance of class members from more than one parent.

Multithreaded program

A program that simultaneously supports more than one thread of execution.

Mutually exclusive

Either but not both.

Naming context

A context or scope in which identifiers are unique.

Natural logarithm

A logarithm that is computed using Euler's constant as a base.

Nested class

A class that is declared as a member of another class or interface.

Non-deterministic

Cannot be predicted or determined.

Numeric promotion

The conversion of numeric values to a larger type to support operations on that type.

Object

An instance of a class. A executable unit of code that contains data (field variables) and provides operations for accessing that data (methods).

Optional

An Optional is a container object that may or may not contain a non-null value. Its isPresent() method returns true if it contains a non-null value, and false otherwise. Its get() method returns the non-null value if it contains a non-null value, and throws a NoSuchElementException otherwise. This implies that when a method returns an Optional, you must, as a practice, check if it contains a non-null value before asking it for the value.

Order of evaluation

The order in which expressions are evaluated.

Package

A collection of related classes and interfaces that are organized into a separate naming context.

Package access

The default access that occurs when no access modifier is specified. Access is restricted to the package in which an item is declared. Also referred to as friendly access.

Painting

The process of drawing to an area of the screen.

Painting thread

A background thread that determines when a portion of the screen needs to be painted or repainted.

Polar coordinates

Coordinates that are expressed in terms of an angle and radius values.

Polymorphism

Having many forms.

Precedence

The order in which operations are performed.

Preemptive scheduling

An approach to scheduling in which the highest priority thread continues to execute until it enters a wait state or a higher priority thread comes into existence.

Primitive type

One of the following data types: boolean, byte, char, short, int, long, float, and double. Primitive types are collections of values and are not objects.

Radians

A unit of angular measurement.

Random number

A number that is produced by a random number generation algorithm. Random numbers appear to be random.

Right associative

Operations that are right associative are performed in a right to left manner. That is, x op y op z is evaluated as x op (y op z).

Runtime exception

An exception that is thrown by the Java runtime system.

Scheduler

The part of an operating system that assigns threads to CPUs. Also referred to as the thread scheduler.

Scheduling

The assignment of threads to CPUs.

Scope

The extent of the context of a definition.

Serialization

The process of writing an object to a stream.

Serialize

To write to a stream.

Serialized

Written to a stream.

Short-circuit

A boolean operation in which one operand determines the result of the operation.

Signature

The name of the method and the number and types of formal parameters to the method.

Single inheritance

The inheritance of class members from a single parent.

Statement block

A sequence of statements enclosed in brackets.

Static initializer

A block of code that is used to initialize a static variable.

Stream

A sequence of characters or bytes.

Strict subclass

A subclass that is not the class itself.

Subclass

A class that extends another class. All classes are a subclass of themselves.

Superclass

A class that is extended by another class.

Synchronization

The coordination of multi-thread access to shared objects.

Thread

A sequence of statements that is executed as part of a program.

Thread priority

A ranking of threads that determines their likelihood of being scheduled.

Thread scheduler

The part of an operating system that assigns threads to CPUs. Also referred to as the scheduler.

Time slicing

A scheduling approach in which a thread executes for a slice of time and then enters a waiting state while another (possibly same) thread is scheduled.

Top-level class

A class that is not nested or a static inner class.

Trigonometric functions

Functions that relate the lengths of line segments, their ratios, and angle measurements.

Unicode

A 16-bit character set that includes ASCII and provides support for international characters.

Unreachable object

An object that is no longer accessible to a program.

UTF

A variation of Unicode referred to as the Universal Character Set Transformational Format (UTF).

Variable

An identifier of a specific type that is used to store a primitive value or reference an object.

Wrapper classes

Classes of java.lang that encapsulate the primitive types.

Xy-coordinates

The Cartesian coordinate system limited to the xy-plane.