JAVA BY DURGA SIR

Java file contain any number of class but only but atmost one can be decleared as public.
If there is no public class the we can use any name for java program .
If there is a public class name of the program should be a class name.
Java file name is depend on the name of the public class.
We can use 0 or 1 public class in java file.

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There is two types of import statement. -Implicit import import java.util* -Explicit import import java.util.ArrayList

java.lang package is already imported in program .
Default package are not need to import like self directory package.
Using Explicit import is a good practice for writing a code.
Whenever we import a package all the all the classes and interfaces present in that packege is by default avalible but not a sub package class.
If you want to use any class in sub package then complesary we have to write import statement until subpackage level.

if there is class is java -> util -> regex -> Pattern

Package is the encapsulation/groping mechanism to group related calsses and interfaces into a single unit.
With the help of package we can avoid naming conflict.
Maintainability
Security

package is keyword in java.
To declear the package we write in header of package package com.mech2it.ocja
This is the universal naming conventation that is used to name the package.
We use domain name because it has its own unique identity
For compiling the java package we cannot use javac filename.java.
We use javac -d . filename.java
-d is stand for the destination where you want to save the .class file.
So the class file will save in /com/mech2it/ocja
And for run the code java com.mech2it.ocja.ClassName
In any java program only 1 package statement is allow.
If you want to import package, package must be decleared in the first line of program. Order for import and package

    package com.mech2it.ocja		// Atmost 1 //
    import java.util.*				
    // Any Number //
    class/interface/enum			// Any Number //

shreeshailaya / basic