More than one!!

[Niyas Ahmed Sheikh]

public interface C 
{
   void ex();
}
 
public interface B 
{
   void ex();
}
 
public class AA111 implements B,C
{
  public void ex()
  {
     System.out.println("aaaaaaaaa");
  }
 
  public static void main(String args[])
  {
     AA111 a = new AA111();
     a.ex();
  }
}

Error Message:
AA111.java:1: class C is public, should be declared in a file named C.java
public interface C
^
AA111.java:6: class B is public, should be declared in a file named B.java
public interface B
^
2 errors

Why if I am using more than one 'public' class or interface raises an error?

[Ernest Friedman-Hill]

As the error messages imply, a public class X must be in a file named X.java. That's just the rule. You can include any number of nonpublic classes in a single file, however.