In C++, it is always possible to have one class nested inside other or
for that matter, a data structure nested inside other data structure.
Something like:

class A
{
   public:
     struct A1
      {
            char a[10];
            char b[10];
      } a1;
     struct A2
      {
            char a2[10];
            char b2[10];
      } a2;
       ...........

};

What i am struggling with is, i am searching for similar representation
for a java class.
I tried doing it as:

public class  Temp
{
  class A1
  {
      public String a1;
      public String b1;
  };
  class A2
  {
      public String a2;
      public String b2;
  };

   ..............
};

This gets compiled but what i see is n no. of .java files get generated
named:

Temp.java
Temp$A1.java
Temp$A2.java

This behavior is coming as a surprise package to me.
I agree i dont't know much of java and am a begineer in this.