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
orfalse
. -
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
andcatch
. -
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. |