![A Simple Java Program
//First Java program single line comment
public class Hello
{
/* Description: multi line comment
Writes the words "Hello Java" on the screen */
public static void main(String[] args)
{
System.out.println("Hello Java");
}
}
Note:
Class name : Hello
Keywords : public, static, void
Data type : String
Array name : args](https://image.slidesharecdn.com/unit1-240129150753-0c9f60f9/85/unit1-pptx-15-320.jpg)
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unit1.pptx
- 1. Unit 1 Introduction to Java
- 2. What is Object-Oriented Programming? • Object-oriented programming (OOP) is a programming standard based on the concept of “objects”. • These objects can contain data known as attributes and code known as methods. • The core concept of the object-oriented approach is to break complex problems into smaller objects.
- 3. Introduction to Java • Java is object-oriented programming language where programs are written using classes. • It allows application developers to write once, and run anywhere (WORA) • This means that compiled Java code can run on all platforms that support Java without the need for recompilation. • Java is widely used for developing applications for desktop, web, and mobile devices. • Java is simple, robust, and secure.
- 4. Explain Java Features 1. Simple, easy and familiar : – Java is easy to learn because its syntax is just like c++. – It is simple because it does not use header files and does not use pointers 2. Compiled and Interpreted : – Java code is translated into byte code after compilation and the byte code is interpreted by JVM (Java Virtual Machine). 3. Platform Independent : – Compiler converts source code to bytecode and then the JVM executes the bytecode generated by the compiler. – This bytecode can run on any platform like Windows, Linux, or macOS which means if we compile a program on Windows, then we can run it on Linux and vice versa. 4. Object-Oriented : – Java is Object oriented - which means no coding outside of class definitions, including main(). 5. Robust : – Robust means inbuilt capabilities to handle errors/exceptions.
- 5. 6. Secure : – it enables to develop virus-free systems. – It has strong authentication techniques . 7. Multithreaded : – It is possible to write a single program that can perform many tasks simultaneously. 8. Dynamic flexibility : – Java gives us the flexibility to add classes, new methods to existing classes, and even create new classes through sub-classes.
- 6. What is Java Architecture. Explain • Java Architecture is a collection of components JVM, JRE, and JDK. • Java Architecture explains each and every step of how a java program is compiled and executed. • Java Architecture can be explained by using the following steps: – There is a process of compilation and interpretation in Java. – Java compiler converts the Java code into byte code. – After that, the JVM converts the byte code into machine code. – The machine code is then executed by the machine.
- 8. Java Virtual Machine • The main feature of Java is Write Once Run Anywhere. • Java Virtual Machine makes it possible to write our code once and use it on any operating system. • JVM converts byte code into machine code. • It loads the code into memory, verifies it and then executes the code
- 9. Java Runtime Environment and Java Development Kit • The JRE contains libraries and software needed by your Java programs to run. • JRE takes our Java code, uses the required libraries, and then starts the JVM to execute it. • JDK is a software development environment used in the development of Java applications and applets. • Java Development Kit contains JRE, a compiler, an interpreter , and many development tools in it.
- 10. List Java Applications • Mobile App Development : – The Java programming language is used for building android applications . • Eg. Spotify and Twitter • Desktop GUI Applications : – Java provides tools which contain pre-assembled components for developing the GUI based desktop application. • Web-based Applications : – Java is used for developing the web-based application using Servlet and JSP. • Gaming Applications : – Java is widely used for developing gaming applications – Eg. Minecraft, Mission Impossible III, etc.
- 11. • Cloud-based Applications : – Java provides the environment to develop cloud-based applications – The cloud applications are widely used to share data between companies or to develop applications remotely. • IoT Applications : – IoT is found almost in all the small devices such as smartphones, wearables, smart lighting, TVs, etc. – For developing the IoT application Java is used, because of its security, flexibility, and versatility.
- 12. Describe structure of Java program A Java program involves the following sections: • Documentation Section • Package Statement • Import Statements • Interface Statement • Class Definition • Main Method Class – Main Method Definition
- 13. • Documentation Section Comments can be written in this section. They help the programmer to understand the code. These are optional • Package statement A package is a group of classes that are defined by a name. If it is required to declare many classes within one element, it can be declared within a package. It is an optional part of the program. package keyword is used to create a a package. Eg. package program; • Import statement This statement is used if it is required to use a class of another package by specifying the package name and the class name separated with a dot operator. Eg. import calc.add; • Interface statement Interfaces are like a class that includes a group of method declarations. It's an optional section and can be used when programmers want to implement multiple inheritances in a program.
- 14. • Class Definition A Java program may contain several class definitions. Classes are the essential elements of any Java program. • Main Method Class Every Java program requires the main method, which is the starting point of the program. There may be many classes in a Java program, but, only one class defines the main method. Methods contain data type declaration and executable statements.
- 15. A Simple Java Program //First Java program single line comment public class Hello { /* Description: multi line comment Writes the words "Hello Java" on the screen */ public static void main(String[] args) { System.out.println("Hello Java"); } } Note: Class name : Hello Keywords : public, static, void Data type : String Array name : args
- 16. Write steps for Compiling and Executing a Java program taking an example of a simple Java program Steps to save the file, compile, and execute the program. • Open notepad and add the Java code. • Save the file as: Hello.java. • Open a command prompt window and go to the directory where you saved the java code. • Type javac Hello.java and press enter to compile your code. If there are no errors in your code, the command prompt will take you to the next line. • Now, type java Hello to run your program. • You will be able to see Hello Java printed on the screen.