Can we create empty
java file, can we compile and execute it?
Yes, but after compilation we do not have .class. so we
cannot execute.
Can we create empty class;
can we compile and execute it?
Yes we can create and compile empty class. Compiler
generates .class file with that class name. we cannot execute this class
because this class does not have main method. It leads to exception.
When should be the
java file name and class name be the same?
If class is declared as public, file name should be the same
as the public class name, else its name can be user defined.
If a java file has
multiple classes what is the java file name?
Public class name. If there no public class than java file
name can be user defined.
In java file we can define only one public class and
multiple non- public class names.
If we compile
multiple classes’ java file, how many .class files are generated by compiler?
Compiler generates .class files as many class definitions as
we have in that java file. Compiler generates .class file separately for every
class with that class name.
User Defined method
and Predefined method: Developer defined method is called user defined or
custom method. Java software developers given method is called predefined
method. It means already implemented methods are called predefined methods. Ex:
println () method.
User Defined and
Predefined classes: Developer defined class is called user defined or
custom class. Java Software developers given class is called predefined class.
It means already implemented classes are called predefined classes. Ex: System,
String…
If a class does not
have main method, how can we execute that class user defined methods?
We should use another class main method. We should call this
method with its class name. In projects, we do not write main method in every
class. Instead we write main method in one class, and we will call all other
classes’ methods from this class’s main method for testing.
Basically main method
is given to start class logic execution but not for developing logic directly.
We can define user defined methods with same name in
multiple classes. While calling those methods we must use that method’s class
name.
We can call main method explicitly with this syntax:
main(new String [0]);
Println () method
places the cursor in the next line after printing current output. So that the
next coming output will be printed in next line.
But whereas print ()
method places the cursor in the same line after printing current output. So that
next coming output will be printed in same line.
Naming Conventions:
Naming a class:
class name should be “Noun”, and should be in title case “every word first
letter should be capital”
Naming a Variable:
Variable name should be “Noun”, and should be in case “every word first letter
should be small after that every word first letter should be capital”
In final variables
all its letters should be capital and words must be connected with ‘_’.
MIN_BALANCE
Naming a Method: Method
name should be “Verb”, because it represents action, and should be in case “every
word first letter should be small after that every word first letter should be capital
and should follow ()”
Ex: getUserName()
Naming Package: all
letters are small, and its length should be a short as possible.
