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Here, we will learn what happens while we compile and run the Java program.

Java at Compile time?

In Java, programs are not compiled into executable files,they are compiled into bytecode , then JVM (Java Virtual Machine) executes this at runtime. Java source code is compiled into bytecode when we use javac compiler. Bytecode is stored on disk with a file extension like .class.

At Runtime?

Runtime is the final phase of the program life-cycle in which the machine executes the program’s code and following steps are performed:

Now we will cover some point for interview purpose:

• we can save a java source file by other name than the class name. if the class is not public

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

In above program If we can save program using Test.java,
compile program using javac Test.java command and run using java Basic command then program will work correctly

Output

Hello World

• we can write multiple classes in a java program and below is the example

class Computer {
   void computerMethod() {
      System.out.println("Power Up! computer is working fine…");
   }

   public static void main(String[] args) {
      Computer my = new Computer();
      Laptop your = new Laptop();
      my.computerMethod();
      your.laptopMethod();
   }
}

class Laptop {
   void laptopMethod() {
      System.out.println("Power Up! laptop is working fine…");
   }
}

Output

Power Up! computer is working fine…
Power Up! laptop is working fine…