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Java HelloWorld Example

Let’s write our first java program Console Output: Hello World. Java is strictly typed programming language. We need simple editor such as notepad, or an IDE like Eclipse. And JDK installed, setup for compiling and running our program. -  Any Java application consists of collections of classes, packages and can also be nested inside other classes. One thing to remember that every java application must have an entry point and that is main method and it must be static, declared public and accept array of string Main method never returns a value and must return void.   Verify Java path is set: Type java version and enter Lets analyze the structure of the above Java program   Line 1. public class HelloWorld - We are creating class named HelloWorld and declaring it as public class - is the keyword used to create a class. Line 2. Main is method - required for stand-alone programs args[] - Main method has an array of string as an argument. Main method can take input for use within the program Line 3. System.out.println("Hello World !") - Displays the output on the console. Here we have string literal and it can be an argument passed through main method as well. we are going to discuss more about classes, methods in coming tutorials.   Compile Java code: --------------------- 1. Java code is called source and save the course code as HelloWorld.java file 2. Use Command prompt and Check Java path if not set the path to your practice directory 3. Now lets compile our Java file. type javac HelloWorld.java and press enter. 4. Java is strictly typed language and will display syntax errors if any. If everything is fine javac will return command prompt 5. You can check with dir command or practice folder to see HelloWorld.class file which is class file compiled by Javac. 6. This class file is the Java byte code file and to execute simply type java HelloWorld.class and press enter. 7. Done - you will see the output of Hello World on the console.   Errors in Java code ----------------------------   We just now completed simple program and got the output as expected. Small code which has few lines of code or large program with multiple lines of code error checking is being done and needs to be corrected before class file can be compiled and run.   some general errors are   1. Classpath - not correct/ not set Watch Learn how to set classpath under installation and setup 2. Verify Java/javac command to run from your current / practice directory 3. Verify that the class file is in the classpath. Source files must be named after the public class they contain, Appending the file suffix .java, for example, HelloWorldApp.java. It must first be compiled into bytecode, using a Java compiler, producing a file named HelloWorld.class. - - Only then can it be executed, or "launched". The Java source file may only contain one public class, but it can contain multiple classes with other than public access and any number of public inner classes. When the source file contains multiple classes, make one class "public" and name the source file with that public class name. The name of the class file is the name of the class, with .class appended The keyword public denotes that a method can be called from code in other classes