Java Programming: Writing Your First Java Program, Study notes of Computer Science

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Java Intro

A First Java Program

//The Hello, World! program in Java

public class Hello {

public static void main(String[] args) { System.out.println("Hello, World!"); }

A First Java Program

public class Hello {

}

• Definition for the class Hello
• Class Hello MUST be defined in a file named Hello.java
• The class definition is enclosed in {}

A First Java Program

public static void main(String[] args) { }

• Every Java application must have a main method
• The header of every main method looks the same
• The method is enclosed by {}
  • Whitespace is ignored
  • Proper indentation is not required by the compiler
    • But, it is required by the instructor...

Java

High level Code

Compiler

Interpreter Output (JVM)

Bytecode

Writing/Compiling/Running

1)Write the program using your favorite text editor –

save a class classname into file classname.java

2)Open a terminal window and cd into the directory

where your code is saved

3)To compile, type javac classname.java

4)Fix any errors and go back to step 3

5)To run, type java classname