Private Interface example

[vinothg]

Just thought of posting this example about private interface which i learned from bruce eckel book "Thinking in Java"

An interface can be nested within a class or another interface. If the interface is nested within a class it can be public or private. But if a interface is nested within a interface it should be public which is by rule.

I was wondering what will be the use of private interface within a class. Then came up with this design.

class librarian {

private interface libraryRules{
void takeHome();
}

public class book implements libraryRules{
private book() {}
public void takeHome(){
System.out.println("takeHome this book");
}
}
public static libraryRules getPermission(librarian ob1){
libraryRules obj = ob1.new book();
return obj;
}

public void gotPermission(libraryRules tmp) {
tmp.takeHome();
}
}

public class library{
public static void main (String arg[]){
librarian obj = new librarian();
obj.gotPermission(librarian.getPermission(obj));
}
}