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Regarding class files

Class files:-Regarding class file or dot class file also known as byte code of class, in a java programming language we can use any number of classes in our program. After compilation all classes convert into individual .class file.

Example:-

class A
{
}
class B
{
}
class C
{
}
class Student
{
public static void main(String[]args)
{
System.out.println("Well-come to my java blog");
}
}

We can save above program to any classname.java or we can use any other name.java, there is no compulsion for java file name. But recommended to save by that class name which having main method.

I saved the above file to Student.java name. Before compilation my C:\JAVATECH folder contain only one java file.

Student.java

For  compilation.

C:\JAVATECH>javac  Student.java

After compilation my C:\JAVATECH folder contains five files, one java file as previous and four .class files.

Student.java
Student.class
A.class
B.class
C.class

For Run:-

C:\JAVATECH>java Student

Well-come to my java blog

If we save above program b y A.java name then no issue we can do this.

For  compilation.

C:\JAVATECH>javac  A.java

After that successfully program will compile and generate .class files same as above.

For Run:-

C:\JAVATECH>java A

Error: Main method not found in class A, please define the main method as:
   public static void main(String[] args).

Because jvm search main method in A.class file only.
So for successfully execution we have to use below commands.

C:\JAVATECH>javac  A.java
C:\JAVATECH>java Student

Well-come to my java blog

In the above program we can write main method in every class.

class A
{
public static void main(String[]args)
{
System.out.println("Well-come to my java blog  A class main method");
}

}
class B
{
public static void main(String[]args)
{
System.out.println("Well-come to my java blog  B class main method");
}

}
class C
{
public static void main(String[]args)
{
System.out.println("Well-come to my java blog C class main method");
}

}
class Student
{
public static void main(String[]args)
{
System.out.println("Well-come to my java blog Student class main method");
}
}

We can save above program by any class name or we can use any other name for (.java) file and run by any .class file because every class having main method. Suppose above program is saved by Test.java name.

C:\JAVATECH>javac Test (compile once only)
C:\JAVATECH>java Student

Well-come to my java blog Student class main method.

C:\JAVATECH>java A

Well-come to my java blog A class main method.

C:\JAVATECH>java B

Well-come to my java blog B class main method.

C:\JAVATECH>java C

Well-come to my java blog C class main method.



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