IT Module 1

Flashcards about the core concepts of Java programming

Program / Software

A set of step-by-step instructions that tells your computer what to do and produce the results you want.

Programming Language (PL)

A set of rules that tells a computer what operations to perform.

Java

An object-oriented, class-based, secured, and general-purpose programming language.

OAK

The first official name of Java.

JDK (Java Development Kit)

A Java software development environment from Oracle. It includes the JVM, compiler, debugger, and other tools for developing Java.

JRE (Java Runtime Environment)

A software layer that runs on top of a computer’s operating system software and provides the class libraries and other resources that a specific Java program needs to run.

JVM (Java Virtual Machine)

An engine that provides a runtime environment to drive the Java Code or applications. It converts Java bytecode into machine language. JVM is a part of Java Run Environment (JRE).

API (Application Programming Interface)

A list of all classes that are part of the Java development kit (JDK)

Bytecode

Program code compiled from source code into low-level code designed for a software interpreter.

Compiler

A program that converts instructions into a machine code or lower-level form so that they can be read and executed by a computer.

Interpreter

A computer program that converts high-level program statements into Assembly Level Language.

Just-In-Time (JIT) compiler

A component of the Java Runtime Environment that improves the performance of Java applications at run time.

Platform

Any hardware or software environment in which a program runs.

Java

High-level, multi-platform, robust, object-oriented, concurrent, secured, and general-purpose computer programming language.

Types of Java Applications

Desktop Applications, Web Applications, Enterprise Applications, Mobile Applications

Web application technologies in Java

Servlets, JSP, Spring, Hibernate

Java SE (Java Standard Edition)

A Java programming platform that includes core topics like OOPs, String, Regex, Exception, Inner classes, Multithreading, I/O Stream, Networking, AWT, Swing, Reflection, Collection, etc.

Java EE (Java Enterprise Edition)

An enterprise platform mainly used to develop web and enterprise applications; built on top of Java SE.

JavaFX

It is used to develop rich Internet applications. It uses a lightweight user interface API.

Java ME (Java Micro Edition)

A micro platform that is mainly used to develop mobile applications

Object-oriented programming (OOP)

Simplifies software development and maintenance by providing some rules like Encapsulation, Inheritance. Polymorphism and Abstraction

Classloader

Part of the Java Runtime Environment(JRE), which dynamically loads Java classes into the Java Virtual Machine.

Bytecode Verifier

Checks the code fragments for illegal code violating access rights to objects.

Security Manager

Determines what resources a class can access, such as reading and writing to the local disk.

Automatic garbage collection

Runs on the Java Virtual Machine to eliminate objects no longer being used by a Java application.

Java Development Kit (JDK)

A software development environment used to make applets and Java applications. It contains tools required to write Java programs and JRE to execute them.

Java Virtual Machine (JVM)

Provides a platform-independent way of executing Java source code and comes with JIT (Just-in-Time) compiler that converts Java source code into low-level machine language.

Java Runtime Environment (JRE)

Contains the class libraries, loader class, and JVM; needed to run Java programs.

ClassLoader (JVM Architecture)

A subsystem used for loading class files and performs three major functions: loading, linking, and initialization.

Method Area (JVM Architecture)

Stores class structures like metadata, the constant runtime pool, and the code for methods.

Heap (JVM Architecture)

All the Objects, their related instance variables, and arrays are stored.

JVM language Stacks (JVM Architecture)

Stores local variables and their partial results and created simultaneously as the thread is created.

PC Registers (JVM Architecture)

Stores the address of the Java virtual machine instruction that is currently being executed.

Native Method Stacks (JVM Architecture)

Holds the instructions for the native code depending on the native library. It is written in another language instead of Java.

Native Method interface (JVM Architecture)

Allows Java code running in a JVM to be called by libraries and native applications.

Native Method Libraries (JVM Architecture)

A collection of the Native Libraries(C, C++) needed by the Execution Engine.

Local Vars

vars defined inside methods, constructors or blocks, and will be be destroyed after completion

Instance vars

vars within class but outside any method. can be accessed inside any class’s method, constructor or block.

class vars

are declared within a class, outside any method with the static keyword

primitive datatypes

basic types of data, and stores actual values

Reference types

are instantiable calss and arrays , store addresses to locations in memory, also known as wrapper classes

Class loader

is the JVM subsystem used to load class files

Bytecode verifier

checks the code fragments for illegal code that can violate access rights to objects

Interpreter

Read the bytecode stream then execute the instructions

Syntax

are set of rules in programming

Comment

used to document a particular code or program and the compiler does not read it.

Phase1: edit

create the program on the editor and after that it is stored in the disk with the names ending .java

phase 2: Compile Javac

a compiler translates from high level language program to bytecodes and stores them in disks with the ending name .class

Phase 3:load

Class loader compiles and put those byte codes from disk to primary memory

Phase 4: verify

Verify bytecodes to confirm that all byte codes are valid and do not rik Java’s security restrictions

Phase 5 execute

JVM read and translates those bytecodes into a language the computer can understand, then execute the program and store its values in primary memory

class keyword

used to declare a class in java

public

an access modifier that represents visibility, it means that it is visible to all

static

the core advantage of it is that there is no need to create an object to invoke the ___ method

void

the return type of the method, it means that it doesnt return any value

main

represents the starting point of the program

String[] args

is used for command line argument

System.out.println()

used to print statements.

syntax error

will happen if a specific rule is not being followed

identifiers

the names given to entities sych as class,vars, and functions

keywords

are identifiers that have special meanings for the compiler

abstract

specifies that the class is abstract

boolean

this data type specifier mentions taht a particular var is boolean

byte

stipulates a specific byte type var

case

specifies the program to be performed if a particular case is satisfied

catch

during a throw case of error handling, encloses actions to be performed if an exception occurs

break

breaks the control out of a loop

void

renders a method non returnable

char

specifies that the var is of character type

class

specifies the creation fo a new class followed by its name

extends

used to indicate theat the class mentioned after it is the derivation of a superclass

Literals

indentifiers that have a particular value in themselves

Decimal

any number base 10

binary

any number base 2

octal

any number base 8

hexadecimal

any nuber base 16

floating poing decimal

numeric values only using a decimal point. represent fractional numbers

character literals

are literals that deal with characters

single quoted character

all unilength characters enclosed within single quotes

escape sequences

characters preceded by a backlash

unicode representation

represented by \u

comments

are needed whenever the developer needs to add documentation

//

singleline documentation

/* */

multiline documentation

/** */

documentation comment

unicode

is universal international standard character encoding capable of representing most of the worlds written languages.

ASCII

American Standard code for information interchange

Widening

converting one type having a lower type into a higher type

Narrowing

converting higher datatype to a lower data type

Typecasting

when you assign a value of one primitive datatype to another type

Parsing

used to convert the value of one data type to the value of another data type

Concatenation

joining two strings together

JOptionpane

simple way to make a UI component

showMessageDialog()

allows for only a message and an OK button

showConfirmDialog()

allows for various combinations of OK,YES,NO, and CANCEL BUTTON

showOptionDIalog()

will enable you to display buttons containing text of your choice.

showInputDialog()

allows the user to enter arbitrary information in a text field or with a combo box list of values. It provides only OK and CANCEL buttons

Sequence

an action or event leads to the next ordered action in predetermined order.

Branching

altering the flow of program execution by making a selection or choice

Looping

Altering the flow of porgram execution by repetition of the statements()