Step-by-Step Tutorial:

Creating Model Classes:

1. Create a new package in your Java project to hold the model classes that correspond to the classes mentioned in the video.
2. Create a class hierarchy starting with the Program class at the top level and subclasses like Number, VariableDeclaration, Variable, Multiplication, and Addition.

Implementing the Program Class:

1. Define the Program class with a list of expressions as its attribute.
2. Create a constructor for the Program class that initializes the list of expressions.
3. Implement a method addExpression in the Program class to add expressions to the list.

Implementing Model Classes:

1. Implement the Number class with a number attribute and a constructor to initialize it.
2. Implement the VariableDeclaration class with ID, type, and value attributes along with a constructor.
3. Implement the Variable class with an ID attribute and extend it from the Expression class.
4. Implement the Multiplication and Addition classes by extending them from the Expression class and defining the necessary attributes and constructors.

Implementing Visitor Pattern:

1. Create visitor classes such as ExpressionVisitor and ExpressionBaseVisitor to transform the parse tree into model objects.
2. Define visit methods in the visitor classes corresponding to the different nodes in the parse tree.
3. Customize the visit methods by adding labels to the production rules in the grammar file to generate specific visit methods for each node.

Regenerating Antlr Parser Code:

1. Regenerate the parser code after customizing the grammar file to include labels for specific visit methods.
2. Refresh your project in Eclipse to see the updated classes and methods generated by Antlr.

Review and Implementation:

1. Review the generated classes and methods in the ExpressionVisitor and ExpressionBaseVisitor classes.
2. Implement the logic in the visit methods to convert the parse tree nodes into corresponding model objects based on the labels and hierarchy defined.

By following these steps, you can create a structured model hierarchy, implement the necessary classes, customize the visitor pattern, and regenerate the parser code to transform the parse tree into model objects as described in the tutorial video.