Skip to main content

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.



Labels:

Comments

Post a Comment

Popular posts from this blog

Inner classes

Inner Classes:- class inside class or interface called inner class or nested class. Advantage of inner classes is grouping multiple classes and interfaces into a single class. Another big advantage of inner class is that inner class can happily access all the data or variables of outer class directly. Types of Nested classes:- There are two types of nested classes static and non-static nested classes. (A)Non –static inner classes:- 1)     Member inner class 2)     Anonymous inner class 3)     Local inner class (B)Static nested class Example1:-Outer.java class Outer { class Inner { void disp() { System.out.println("Hello This is Inner class Method"); } } public static void main(String[]args) { Inner in=new Inner(); in.disp(); } } Output:- C:\JAVATECH>javac Outer.java Outer.java:12: error: non-static variable this cannot be referenced from a static context Inner in=new Inner(); ...
Post a Comment
Read more

command line options

Command Line Argument:- value supplied to the main method String array from the run time or from command prompt called command line argument. All the values will be String. When we supplied value from command prompt automatically an array will be created of that length (number of arguments). Example1:- Command.java class Command { public static void main(String[]args) { System.out.println("Demo of Command Line"); } } Output:- C:\JAVATECH>javac Command.java C:\JAVATECH>java Command command com om Demo of Command Line Example2:- Command.java class Command { public static void main(String[]args) { System.out.println("Demo of Command Line"); System.out.println(args[0]); } } Output:- C:\JAVATECH>javac Command.java C:\JAVATECH>java Command command com om Demo of Command Line Command Example3:- Command.java class Command { public static void main(String[]args) { System.out.println("Demo of ...
Post a Comment
Read more

Example of Variables

Example1:- class Student { String name; int roll; String address; String course; String instName; void getData() { System.out.println("Student information is:-"); System.out.println("Name: "+name); System.out.println("RollNumber: "+roll); System.out.println("Address is: "+address); System.out.println("Course is : "+course); System.out.println("Institute is : "+instName); } public static void main(String[]args) { Student s=new Student(); s.getData(); } } Output:- C:\JAVATECH>javac Student.java C:\JAVATECH>java Student Student information is:- Name: null RollNumber: 0 Address is: null Course is : null Institute is : null In the output 0 is default value of integer variable and null is default value of all secondary data types. In the above program we have two types of variables, instance variable and local variable. Total five instance variabl...
Post a Comment
Read more