Composite

The syntax of a simple "while" language is shown below:

    Statement   ::= Assignment | Conditional | While | Compound
    Assignment  ::= Var := Expr
    Conditional ::= if Expr then Statement else Statement
    While       ::= while Expr do Statement
    Compound    ::= begin Statement; ...; Statement end

Define classes, using the Composite pattern, for representing programs in this language. For example, the following factorial program

    begin
      fact := 1;
      while (n > 1) do
        begin
          fact := fact * n;
          n := n - 1
        end
    end

is constructed, using the classes you are expected to define, by this Java declaration and initialization

    Statement factorial = new Compound (
        new Assignment ("fact", new Expr ()),
        new While (new Expr (), new Compound (
            new Assignment ("fact", new Expr ()),
            new Assignment ("n", new Expr ()))));

To simplify the code, expressions are represented by a trivial placeholder. Include in your classes methods to pretty print a program. The expected output when object "factorial" is printed is

    begin
      fact := expression;
      while expression do
        begin
          fact := expression;
          n := expression
        end
    end