Java: Why can a file not have more than one public class

Question

public class A
{
}  

public class B 
{
    public static void main(String[] args) 
    {
    }
}

Why cant we declare both class as public?
Why only Main class can be public? i know that by making class public ,it will allow you access in package ok ,but what if i make

     public    class a
     { 

     }
    class B
     {
    public static void main(String[] args) 
    {

     }
  }

why this code give error do we really need to notify that main class is public bcoz every class is public

A public class requires saving with the same file name as the class name. — Lion, Jun 06 '13 at 20:32
No by default, a class is applied *no modifier* which is different in nature from public. — Lion, Jun 06 '13 at 20:38

Adam Siemion · Answer 1 · 2013-06-06T20:40:33.117

4

Because one .java file can contain only one public class.

If you want these two classes to be public they have to be put into two .java files: A.java and B.java.

From the JLS 7.6. Top Level Type Declarations:

This restriction implies that there must be at most one such type per compilation unit. This restriction makes it easy for a Java compiler to find a named class within a package. In practice, many programmers choose to put each class or interface type in its own compilation unit, whether or not it is public or is referred to by code in other compilation units.

edited Jun 06 '13 at 20:40

answered Jun 06 '13 at 20:31

Adam Siemion

15,569
7
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but by default every class in java is public ..so is it really important to mention it..and if,then why they said so.. – user2461247 Jun 06 '13 at 20:34
Not every class in java is public by default. They are package-private by default – waldol1 Jun 06 '13 at 20:37
1

thanks guys it realy helps...:) – user2461247 Jun 06 '13 at 20:46
no if we put the package thing apart then what will happen,, – user2461247 Jun 06 '13 at 20:48
@user2461247 : How do you *put the package thing apart*? A Java class is always inside a package even though you don't mention so. In which case, it uses a default package. – Lion Jun 06 '13 at 20:52
This does not answer the question. – Don Larynx Apr 02 '15 at 12:14
@DonLarynx Then write your own answer. – Adam Siemion Apr 02 '15 at 16:16
to be more specific, your answer uses circular reasoning. Why cant we have more than one public class? Because we cant. You beg the question. – Don Larynx Apr 02 '15 at 18:49

score 2 · Answer 2 · answered Jun 06 '13 at 20:33

2

The filename for a Java class is the public class' name. You cannot have 2 file names, hence you cannot have 2 public classes.

answered Jun 06 '13 at 20:33

Vaishak Suresh

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Java: Why can a file not have more than one public class

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