84.txt

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Abstract class 
An abstract class is a type of class that is not allowed to be instantiated. The only reason it exists is to be extended. Abstract classes contain methods and variables common to all the subclasses, but the abstract class itself is of a type that will not be used directly.

Abstract method 
An abstract method is a method declaration that contains no functional code. The reason for using an abstract method is to ensure that subclasses of this class will include this method. Any concrete class (that is, a class that is not abstract, and therefore capable of being instantiated) must override this method.

Access modifier
 An access modifier is a modifier that changes the protection of an element.

Adapter classes 
Adapter classes are provided to help the programmer develop classes that implement the event interfaces. Also, adapter classes are classes that implement a particular listener interface with empty methods. This means that you can subclass an adapter and then override only the methods that you are interested in.

Anonymous class 
You use an anonymous class when you want to create and use a class but do not want to bother with giving it a name or using it again.

Anonymous inner classes
 Anonymous inner classes are local inner classes that do not have a class name. Using anonymous inner classes is most effective when they are small and implement only a single or very few small methods.

API 
Application Programmers Interface. This term refers to a set of related classes and methods that work together to provide a particular capability.

Array
 Arrays are homogenous data structures implemented in Java as objects. Arrays store one or more of a specific type and provide indexed access to the store.

Automatic variables
 Also called method local variables. Automatic variables are variables that are declared within a method and discarded when the method has completed.

AWT 
The AWT is Java’s Abstract Windowing Toolkit. This is a platform independent API that provides a user interface capability.

Base class 
A Base class is a class that has been extended. If class d extends class b, class b is the base class of class d.

Blocked state
 A thread that is waiting for a resource, such as a lock, to become available is said to be in a blocked state. Blocked threads consume no processor resources.

Boolean literals
 Boolean literals are the source code representation for Boolean values. Boolean values can only be defined as either true or false.

BorderLayout layout manager 
The BorderLayout layout manager divides the container into five areas. These areas are NORTH, SOUTH, EAST, WEST, and CENTER. The name of the area indicates where the component will be placed. All directional references are relative to the top of the container, which is considered NORTH.

Call stack A call stack is a list of methods that have been called in the order in which they were called. Typically, the most recently called method (the current method) is thought of as being at the bottom of the call stack.

CardLayout layout manager 
The CardLayout layout manager treats each contained component as a card, with only one card being visible at any given time. Whichever component was added first will be visible first when the container is displayed.

Casting
 Casting is the conversion of one type to another type. Typically, casting is used to convert an object reference to either a supertype or a subtype, but casting can also be used on primitive types.

char 
A char is a primitive data type that holds a single character. 

Character literals 
Character literals are represented by a single character in single quotes, such as ‘A’.

Child class
 See Derived class.

Class
 A class is the definition of a type. Classes describe an entity’s public interface. See also Base class; Derived class; Inner classes.

Class constructors
 Class constructors are able to call overloaded constructors both in their class and in their superclass. To call another constructor in the same class, you can place a this() in the first line of the body in the calling constructor. Placing this() in any other place will result in a compiler error.

Class members
 Class members are variables defined at the class level. These include both instance variables and class (static) variables.

Class methods
 A class method, often referred to as a static method, may be accessed directly from a class, without instantiating the class first.

Class variable
 See Static variable.

Collection
 A collection is an object used to store other objects. Collections are also commonly referred to as containers. Two common examples of collections are Hashtables and Vectors.

Collection interface
 The collection interface defines the public interface that is common to all collection classes.

Collections framework
 Three elements (interfaces, implementations, and algorithms) create what is known as the collections framework.

Command string
 The command string contains data about the source or cause of an event. An action event that is the result of a Button being activated contains the Button’s text. An action event that is the result of the ENTER key being pressed in a TextField component returns the entered text. Similarly, the text that represents a MenuItem or item in a list component is returned when a MenuItem or List is the source of the action event.

Comparison operators
 Comparison operators perform a comparison on two parameters and return a Boolean value indicating if the comparison is true. For example, the comparison 2<4 will result in true while the comparison 4==7 will result in false.

Components 
Components are the base class and provide functionality for defining the appearance of the widget, the response (if any) to various events, and, finally, the instructions on how to render itself. A component generates a ComponentEvent when the component’s size, position, or visibility has changed. ComponentEvents are for notification purposes only.

Conditional operators
 Conditional operators are used to evaluate Boolean expressions, much like if statements, except instead of executing a block of code, a conditional operator will assign a value to a variable.

Constructor 
A method of a class that is called when the object is created, or instantiated. Typically, constructors initialize data members and acquire whatever resources the object may require.

Container components 
A container component, such as Panel, generates a ContainerEvent as a result of a child component being added or removed from the container. ContainerEvents are for notification purposes only. The AWT automatically handles changes to the contents of a container component internally.

Containers
 Containers are specialized components that hold other components. Because containers themselves are components, you can nest containers to achieve a desired layout. In this context, containers are part of the AWT.

Continue statement 
The continue statement causes the current iteration of the innermost loop to cease and the next iteration of the same loop to start if the condition of the loop is met. In the case of using a continue statement with a for loop, you need to consider the effects that the continue has on the loop iterator.

Deadlock
 Also called deadly embrace. Threads sometimes block while waiting to get a lock. It is easy to get into a situation where one thread has a lock and wants another lock that is currently owned by another thread that wants the first lock. Deadlock is one of those problems that are difficult to cure, especially because things just stop happening and there are no friendly exception stack traces to study. They might be difficult, or even impossible, to replicate because they always depend on what many threads may be doing at a particular moment in time.

Deadly embrace 
See Deadlock.

Decision statement 
The if and switch statements are commonly referred to as decision statements. When you use decision statements in your program, you are asking the program to calculate a given expression to determine which course of action is required.