JVM (Java Virtual Machine) §
- Java is platform independent because it run on the JVM, on top of any system. In other words, any system that has a JVM can run Java applications.
- JVM however is platform dependent.
- In order to run a Java application in the JVM,
- Supply the program byte-code
- Specify the first file (it should have a main method)
- Expected signature of the main method:
public static void main
JRE (Java Runtime Environment) §
JRE = JVM + libraries- Enough to run Java applications
JDK (Java Development Kit) §
- Used to develop Java applications
JDK = JRE + Other programs (javac, etc.)- Developers use JDK, while users need only JRE to run the applications
- Thus Java is referred to as “WORA” (Write Once Run Anywhere)
Java setup §
A Simple Java Program §
// Hello.java file
class Hello { // Need a class as Java is strictly object-oriented
public static void main (String a[]) { // JVM looks for this method
System.out.println("Hello World");
}
}
javac Hello.java # Compiles and creates a new Hello.class file
java Hello # Executes using JVM
Refs §
- https://www.youtube.com/watch?v=NHrsLjhjmi4