Introduction to Java Basics
Java Overview
Why Java
Java is a general-purpose, computer programming language that is:
Concurrent.
Class-based.
Object-oriented.
Designed to have as few implementation dependencies as possible.
Java is intended to let application developers write once, run anywhere (WORA).
Compiled Java code can run on all platforms that support Java without the need for recompilation.
There were five primary goals in the creation of the Java language:
Simple, object-oriented, and familiar.
Robust and secure.
Architectural-neutral and portable.
Executed with high performance.
Interpreted, threaded, and dynamic.
Java enables users to develop and deploy applications on the Internet for servers, desktop computers, and small handheld devices. Today’s computing is profoundly influenced by the Internet, and Java promises to remain a big part today and in the future:
Java is a general-purpose programming language.
Java permeates the Internet, and is the invisible force behind many applications and devices that power our day-to-day lives. From mobile phones to handheld devices and games, and from navigation systems to e-business solutions. Java is everywhere!
Java History
James Gosling, Mike Sheridan, and Patrick Naughton initiated the Java language project in June 1991. The small team of Sun Microsystems (now a subsidiary of Oracle Corporation) engineers called it Green Team, which was originally designed for small, embedded systems in electronic appliances such as set-top boxes.
As a development of the Green Project, the name was changed to “Oak.”
In 1994, Oak was renamed “Java,” and was released in 1995.
Java 1.0 released in January 23, 1996.
The most current version, “Java 12,” was released in March 2019.
Java Version History
Java Features
Java is a platform-independent language.
Java is simple.
Java is object-oriented.
Java is distributed.
Java is JIT-compiled.
Java is robust.
Java is secure.
Java is multi-threaded.
Java is dynamic.
Java provides Automatic Garbage Collection.
Java includes easy, open-source libraries for the latest technologies.
Java Architecture
Java Architecture is a collection of components (e.g., JVM, JRE, and JDK). It integrates the process of interpretation and compilation, and defines all of the processes involved in creating a Java program.
Java Architecture completes the following stages.
Java compiler converts the Java code into bytecode.
The JVM converts the byte code into machine code.
The machine code is then executed by the machine.
Java Environment
JVM (Java Virtual Machine)
JRE (Java Runtime Environment)
JDK Java Development Kit)
Java Environment - Java Development Kit
Java Development Kit
The Java Development Kit (JDK) is a software development environment used for developing Java applications. It includes the Java Runtime Environment (JRE), an interpreter/loader (Java), a compiler (javac), an archiver (jar), a documentation generator (Javadoc), and other tools needed in Java development.
Java Environment - Java Runtime Environment
Java Runtime Environment
Java Runtime Environment (JRE), also written as Java RTE, provides the minimum requirements for executing a Java application; it consists of the Java Virtual Machine (JVM), core classes, and supporting files.
Java Environment - Java Virtual Machine
Java Virtual Machine
Java Virtual Machine (JVM) manages system memory and provides a portable execution environment for Java-based applications. It includes:
A specification — where requirements of a JVM are specified.
An implementation — a computer program that meets the requirements of the JVM specification.
A runtime instance — an instance of JVM is created whenever a Java command is written on the command prompt to run the Java class.
Java Development Kit Editions
Java technology is both a programming language and a platform. The Java programming language is high-level and object-oriented, and has a particular syntax and style. A Java platform is a particular environment on which Java programming language applications run.
There are four platforms of the Java programming language
Java Platform, Java Standard Edition (Java SE)
Java SE can be used to develop client-side, stand-alone applications or applets. Throughout this course, we will use Java SE 1.8 for development.
Java Platform, Java Enterprise Edition (Java EE)
Java EE can be used to develop server-side applications such as Java Servlets, JavaServer Pages, and JavaServer Faces.
Java Platform, Java Micro Edition (Java ME)
Java ME can be used to develop applications for handheld devices such as cell phones.
Java FX
JavaFX can be used to create rich Internet applications using a lightweight user-interface API. Its applications may be clients of Java EE platform services.
Integrated Development Environment and Eclipse
Java Integrated Development Environments
IDE is the Integrated Development Environment that provides the user interface for code development and testing and debugging features. It helps to organize the project artifacts that are relevant to the source code of the software application. IDEs also have the functionalities to compile and interpret the program, and has the ability to monitor resources such as memory usage and hard disk space checking, etc
Popular IDEs for Java:
NetBeans - Best Java IDE (Free Tier).
IntelliJ IDEA - Best IDE for Java (commercial version).
Eclipse - Most popular Java IDE.
JDeveloper - Java IDE for everything Oracle.
Android Studio - Free Java IDE for Android apps.
Eclipse Integrated Development Environmen
The Eclipse IDE is defined as a platform for developing the computer-based applications using various programming languages such as Java, Python, C/C++, Ruby, and many more. The Eclipse IDE Java-based programming is done in this platform. There are several plugins that can be installed in the platform. The advanced client applications can be developed.
The Eclipse IDE provides the workspace in which a user can bundle all of the projects in a single workspace. In that single workspace, the source files, artifacts, and images can all be stored in the workspace. The user has access to the complete functionality to select the name of the workspace and manage the projects in a single workspace.
Java Program Overview
Anatomy of a Java Program
Let’s explore the anatomy of a Java Program, including:
Class name.
Main method.
Statements.
Statement terminator.
Reserved words.
Curly Braces.
Parentheses.
Inline Comments.
Double Quotation Marks.
Class Name
What is a Class in Java?
Java considers any real-life object (noun) to be a class (e.g., Car, Shape, Bank etc).
Every Java program must have at least one class.
Each class has a name.
By convention, class names start with an uppercase letter.
Entering the main() Method
In order to run a class, the class must contain a method named main().
In the below code, line 3 defines the main() method.
The program execution starts with the main() method. This is the entry point for the JVM.
Executing the Statement
A statement represents an action or a sequence of actions. Every statement in Java ends with a semicolon (;).
The statement System.out.println("Welcome to Java!"); in this program causes “Welcome to Java!” to be printed to the console.
Reserved Words
Reserved words are words that cannot be used as variable names in a Java program because they are part of the syntax of the Java programming language.
Examples of Reserved Keywords: public, class, and static.
The complete list of reserved words (Java Language Keywords) can be found here.
Special Symbols
Curly Braces
A pair of curly braces {} in a program forms a code block that groups statements together.
Curly braces have many uses in Java. In general, they define discrete blocks of code.
Curly braces are always paired.
Parentheses
Parentheses are used to define methods and make calls to methods.
Inline Comments
Two forward slashes (//) begin an inline comment.
Code comments provide information to the programmer; the compiler ignores them.
Double Quotation Marks
Double quotation marks (“”) are used around string literals.
Best Practices - Programming Style and Documentation
Appropriate Comments
Include a summary at the beginning of the program to explain what the program does, its key features, its supporting data structures, and any unique techniques it uses.
At the beginning of the program, include your name, class section, instructor, date, and a brief description of the program:
Single-line comment
// This would be a single-line comment
Multi-line comment
/*This would be a multi-line comment; it could span many lines.*/
Naming Conventions: Classes
Every Java program has at least one class. Larger Java programs include many classes.
All executable code in a Java program is written inside of a method, inside of a class.
Class names should be in Upper CamelCase. Try to use nouns. A class is normally representative of something in the real world:
class CustomerAccount.
class HttpClient.
class BrowserConfiguration.
Naming Conventions: Packages
The Java classes and other program resources (e.g., images and audio used by the program) can be bundled into Packages. Java classes are assigned to Packages, based on the package keyword at the top of the Java file and by their location in a folder structure.
Package names should be written in lowercase. For small projects that only have a few packages, use simple and meaningful names: For example:
package pokeranalyzer.package mycalculator.
Normally, the package names are broken down. For example, for large projects, the package name may start with the company domain before being split into layers or features:
package com.mycompany.utilities.package org.teksystem.training.javadeveloper.
Naming Conventions: Methods and Variables
Methods: Names should be written in lower CamelCase, and include verbs that describe what the method does:
void calculateTax(), string getSurname()
Variables: Names should be written in lower CamelCase and listed in alphabetical character:
The names should represent what the value of the variable represents:
string firstName, int orderNumber
Only use very short names when the variables are short-lived, such as for loops:
for (int i=0; i<20;i++) { //i is only visible in this code block}
Constants: By convention, constant names should be written in uppercase:
static final int DEFAULT_WIDTH.static final int MAX_HEIGHT.
Naming Conventions: Interfaces
Interfaces: Names should be written in upper CamelCase.
Interfaces tend to have a name that describes an operation that a class can perform:
interface Comparable;interface Enumerable;
Note that some programmers like to distinguish interfaces by beginning the name with an "I":
interface IComparable;interface IEnumerable;
Proper Indentation and Spacing
Indentation:
Indentation is critical to a well-crafted code; it makes code readable.
Be aware of whether you are using tabs or spaces to indent. Tabs give programmers more flexibility in how their code appears in their preferred editor; but in some shops, use of spaces is the norm.
Spacing:
Use a blank line to separate segments of the code.
Block Styles
End-of-line style is the norm in many Java shops; although, the extra white space of next-line style is more readable to many developers.
Next-Line Style
Knowledge Check
What is Java?
high-level
object-oriented programming languag
platform independence
Java programs can run on any platform
used extensively in web development
open-source language
Describe at least three Java Features?
Object-Oriented Programming: Java is an object-oriented programming language, which means that it supports the concepts of classes, objects, encapsulation, inheritance, and polymorphism.
Platform Independence: Java programs can run on any platform (such as Windows, Mac, or Linux) as long as a Java Virtual Machine (JVM) is available on that platform.
Garbage Collection: Java has an automatic garbage collection feature, which automatically frees up memory occupied by objects that are no longer being used.
Exception Handling: Java has a robust exception handling mechanism that allows developers to handle and recover from errors and exceptions that occur during program execution.
Multithreading: Java supports multithreading, which allows programs to execute multiple threads concurrently, thus improving performance and responsiveness.
Security: Java has built-in security features, such as the Security Manager and the Java Cryptography Extension, which help ensure the safety and security of Java programs.
Generics: Java supports generics, which allow developers to write code that is more type-safe and reusable.
Annotations: Java has a powerful annotations feature that allows developers to add metadata to their code, which
Describe the Java Environment?
The Java environment consists of two primary components: the Java Development Kit (JDK) and the Java Runtime Environment (JRE).
Java Development Kit (JDK): The JDK is a software development kit used to develop Java applications. It contains tools such as the Java compiler, which is used to compile Java code into bytecode that can be executed on any platform with a Java Virtual Machine (JVM). The JDK also includes other tools such as the Java debugger, JavaDoc, and JavaFX, which are used to develop and test Java applications.
Java Runtime Environment (JRE): The JRE is a runtime environment that is used to execute Java programs. It includes the Java Virtual Machine (JVM), which is responsible for interpreting Java bytecode and executing Java programs. The JRE also includes the Java class libraries, which provide a set of pre-built classes and methods that Java programs can use.
Define JRE and JDK
JRE stands for Java Runtime Environment. It is a software environment that provides the minimum requirements for executing Java programs. The JRE includes the Java Virtual Machine (JVM), which is responsible for interpreting Java bytecode and executing Java programs. The JRE also includes the Java class libraries, which provide a set of pre-built classes and methods that Java programs can use.
JDK stands for Java Development Kit. It is a software development kit used to develop Java applications. The JDK includes the JRE as well as additional tools such as the Java compiler, which is used to compile Java code into bytecode that can be executed on any platform with a JVM. The JDK also includes other tools such as the Java debugger, JavaDoc, and JavaFX, which are used to develop and test Java applications.
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