Java Keywords with Their Definitions and Complete Java Terminology with Definitions

 

Prepared By : Prof. Uday Shah (HOD-IT)

Java Keywords and Their Definitions

A

• abstract – Used to declare a class or method as abstract. Abstract classes cannot be instantiated, and abstract methods must be implemented by subclasses.

• assert – Used for debugging; tests a boolean condition, and throws an AssertionError if the condition is false.

B

• boolean – Data type that can hold only two values: true or false.

• break – Exits a loop or a switch statement immediately.

B (byte)

• byte – Data type that stores an 8-bit signed integer (range: -128 to 127).

C

• case – Defines a branch in a switch statement.

• catch – Used with try to handle exceptions.

• char – Data type for storing a single 16-bit Unicode character.

• class – Used to define a class.

• const – Reserved but not used in Java (for compatibility with C/C++).

• continue – Skips the current iteration of a loop and moves to the next.

D

• default – Specifies the default branch in a switch or provides a default implementation in an interface.

• do – Starts a do-while loop.

D (double)

• double – Data type for storing a 64-bit double-precision floating-point number.

E

• else – Specifies a block of code to execute if an if condition is false.

• enum – Declares a set of named constants.

• extends – Used in class inheritance to indicate a superclass.

F

• final – Used to declare constants, prevent method overriding, or prevent inheritance of a class.

• finally – A block in exception handling that always executes after try and catch.

• float – Data type for storing a 32-bit single-precision floating-point number.

• for – Used to start a for loop.

G

• goto – Reserved but not used in Java.

I

• if – Executes a block of code if a condition is true.

• implements – Indicates that a class implements an interface.

• import – Allows importing other classes or packages.

• instanceof – Tests whether an object is an instance of a specific class or subclass.

• int – Data type for storing a 32-bit signed integer.

• interface – Declares an interface.

• long – Data type for storing a 64-bit signed integer.

N

• native – Declares that a method is implemented in platform-dependent code using JNI.

• new – Creates new objects.

• null – Represents a null reference.

P

• package – Defines a package (namespace) for a group of related classes.

• private – Access modifier; accessible only within the same class.

• protected – Access modifier; accessible within the same package and subclasses.

• public – Access modifier; accessible from anywhere.

R

• return – Exits from a method and optionally returns a value.

S

• short – Data type for storing a 16-bit signed integer.

• static – Used for class-level variables or methods that belong to the class rather than instances.

• strictfp – Ensures floating-point calculations follow IEEE 754 standards.

• super – Refers to the superclass’s methods, variables, or constructors.

• switch – Starts a multi-branch selection statement.

• synchronized – Ensures that only one thread can access a block of code or method at a time.

T

• this – Refers to the current object.

• throw – Used to explicitly throw an exception.

• throws – Declares exceptions that a method might throw.

• transient – Prevents a variable from being serialized.

• try – Starts a block of code for exception handling.

• true – Boolean literal representing logical truth.

V

• var – Used for local variable type inference (Java 10+).

• void – Specifies that a method does not return any value.

• volatile – Indicates that a variable's value will be modified by different threads.

W

• while – Starts a while loop.

Complete Java Terminology with Definitions

A – C

Term	Definition
Abstract Class	A class declared with abstract keyword; cannot be instantiated and may contain abstract methods.
Abstract Method	A method declared without implementation, meant to be overridden in a subclass.
API (Application Programming Interface)	A set of classes and methods provided to interact with the Java library or other services.
Applet	A Java program embedded in a web page that runs in a browser or applet viewer. (Deprecated in modern Java)
AWT (Abstract Window Toolkit)	A set of APIs for creating GUI applications in Java.
Array	A fixed-size collection of elements of the same type stored in contiguous memory.
Bytecode	Platform-independent intermediate code generated by the Java compiler and executed by the JVM.
Class	A blueprint for creating objects; contains fields (variables) and methods.
Classpath	The location(s) from which the JVM or compiler loads classes and packages.
Constructor	A special method used to initialize objects when they are created.
Casting	Converting one data type to another, e.g., int to double (widening) or double to int (narrowing).
Checked Exception	Exceptions checked at compile time; must be declared in throws or handled using try-catch.
Collection Framework	A set of classes and interfaces (like List, Set, Map) for working with data collections.

D – F

Term	Definition
Delegation Event Model	A mechanism in Java for handling events in GUI applications.
Dynamic Binding	Method call resolution at runtime based on the object’s actual type.
Encapsulation	Bundling data and methods into a single unit (class) and restricting access via access modifiers.
Enum	A special Java type used to define collections of constants.
Exception	An event that disrupts the normal flow of a program; handled using try-catch-finally.
extends	Keyword used for class inheritance or interface extension.
final	Keyword used to declare constants, prevent inheritance, or prevent method overriding.
finalize()	A method called by garbage collector before reclaiming an object’s memory. (Deprecated in newer versions)
float	A 32-bit single-precision floating-point number.
Framework	A reusable set of libraries for building Java applications (e.g., Spring, Hibernate).

G – I

Term	Definition
Garbage Collection	Automatic memory management process that frees memory occupied by unused objects.
Generics	Enables type safety in collections and methods by parameterizing data types.
GUI (Graphical User Interface)	A user interface that includes buttons, menus, text fields, etc.
HashMap	A Java collection that stores key-value pairs using hashing for fast lookups.
Heap Memory	Runtime memory area where objects are stored.
HTTPServlet	A class in Java EE for handling HTTP requests and responses.
implements	Keyword used by a class to use an interface.
import	Keyword to include other Java classes or packages in a program.
Inheritance	Mechanism where a class acquires properties and behavior from another class.
Interface	A collection of abstract methods and constants used for defining a contract.
Instance Variable	A variable defined in a class for which each object has its own copy.

J – L

Term	Definition
JavaBeans	Reusable software components written in Java that follow specific naming conventions.
JDBC (Java Database Connectivity)	API for connecting and executing queries on a database.
JDK (Java Development Kit)	Includes JRE plus tools for Java development (compiler, debugger, etc.).
JIT (Just-In-Time Compiler)	Converts bytecode into native machine code at runtime for better performance.
JME (Java Micro Edition)	A version of Java designed for mobile and embedded devices.
JRE (Java Runtime Environment)	Software package that provides JVM and libraries for running Java applications.
JSP (JavaServer Pages)	Technology for creating dynamic web content using Java embedded in HTML.
JVM (Java Virtual Machine)	An engine that executes Java bytecode.
Local Variable	Variable declared within a method or block, accessible only there.
Loop	A control structure for executing a block of code repeatedly (for, while, do-while).

M – O

Term	Definition
main() Method	The entry point of a Java application.
Method Overloading	Defining multiple methods with the same name but different parameter lists.
Method Overriding	Redefining a superclass method in a subclass with the same signature.
Multithreading	Running multiple threads simultaneously for parallel execution.
MVC (Model-View-Controller)	Architectural pattern for separating business logic, UI, and data.
Nested Class	A class defined within another class.
NullPointerException	An exception thrown when trying to use an object reference that has not been assigned.
Object	An instance of a class containing data (fields) and behavior (methods).
Overloading	See Method Overloading.
Overriding	See Method Overriding.

P – R

Term	Definition
Package	A group of related classes and interfaces.
Polymorphism	The ability of an object to take many forms (method overloading and overriding).
PreparedStatement	JDBC statement used for executing parameterized SQL queries.
Primitive Data Types	Basic types like int, char, boolean, float, double, byte, short, long.
Private / Protected / Public	Access modifiers that control visibility of members.
Recursion	Method calling itself directly or indirectly.
Reference Variable	Variable that holds the memory address of an object.
Reflection	API for inspecting and modifying runtime behavior of applications.
ResultSet	JDBC object holding data retrieved from a database query.
RMI (Remote Method Invocation)	Java API for invoking methods on remote objects.
Runtime Exception	Exceptions that occur during program execution and are not checked at compile time.

S – U

Term	Definition
Servlet	Java class that handles HTTP requests and responses in a web application.
Session	A way to store user-specific data across multiple HTTP requests.
Socket	Endpoint for communication between two machines over a network.
Source Code	The .java file containing Java code written by the programmer.
Static	Keyword indicating that a field or method belongs to the class rather than instances.
String	A sequence of characters in Java, represented by the String class.
super	Keyword to call a superclass constructor or method.
Swing	A set of lightweight Java APIs for building GUI applications.
Synchronization	Mechanism to control access to shared resources in multithreaded environments.
Thread	A lightweight subprocess for parallel execution.
Throwable	The superclass of all errors and exceptions in Java.
try-catch-finally	Exception handling blocks in Java.
URL (Uniform Resource Locator)	Address of a resource on the internet.
User Interface (UI)	The part of an application that the user interacts with.

V – Z

Term	Definition
Variable	A named location in memory used to store data.
Vector	A synchronized dynamic array in Java.
Virtual Machine	Software that executes programs like a physical machine (e.g., JVM).
volatile	Keyword to indicate a variable’s value can be modified by multiple threads.
Web Container	Part of a web server that interacts with Java Servlets and JSPs.
Wrapper Classes	Classes that convert primitive types into objects (Integer, Double, etc.).
XML (Extensible Markup Language)	Used for data storage and transfer, often in Java web services.
XSS (Cross-Site Scripting)	Security vulnerability Java web developers must prevent.
Yield	A thread method suggesting the scheduler to give execution to other threads.
ZIP Streams	Java I/O classes to read/write compressed files.