Refactoring Legacy Code Tutorial

Code examples for Refactoring Legacy Code Tutorial.

See the checklist below for the complete list of refactorings applied in the tutorial.

Step 1: Removing the clutter

• Run XMLToJsonTest with coverage.
• Rename variable url to urlToTOC - enables better understanding of the variable's purpose.
• Remove dead/commented code - improves code clarity and maintainability.
• Remove the cast to Element - unnecessary and clutters the code.
• Convert wrapper type Boolean to primitive boolean - avoids unnecessary object creation and potential null pointer exceptions.
• Decompose conditional - extract conditional code to clearly named method.
• Remove else branch with empty body - simplifies the code by removing unnecessary branches.
• Remove unnecessary continue statement - enhances code readability.
• Use isEmpty() to check whether the collection is empty or not.
• Remove unnecessary main method - cleans up the code by removing unused entry points.
• Replace equals("") with isEmpty() - improves readability and performance.

Step 2: Reducing Complexity and Composing Methods

• Simplify hasChildren variable assignment by removing if else statements - reduces nesting and improves readability.
• Inline hasChildren variable - eliminates unnecessary variable and simplifies the code.
• Extract method getNode to reduce complexity before start iterating - breaks down large methods into smaller, more manageable pieces.
• Extract method processElement to handle element processing - Use option+Up Arrow to expand your selection.
• Extract method closeJson to handle JSON closing logic
• Extract method getJsonForDocument to inject a Document instead of obtaining it inside the method.

Step 3: Refactoring to Testability

Introduce further refactorings to improve testability and maintainability.

Replace Function with Command

Replace Function with Command aka Replace Method with Method Object encapsulates behavior in command objects for better testability.

• Extract method toJsonString(String, Element) to convert a Document element to JSON string.
• Create class DocumentElement to represent document elements - encapsulates related data and behavior.
• Add DocumentElement as parameter to toJsonString method.
• Inline method hasChildren - make the code accessible from toJsonString method.
• Convert toJsonString method to an instance method of DocumentElement - improve encapsulation and support polymorphism.
• Extract method hasChildren in DocumentElement class.
• Create constructor DocumentElement(String) - pass arguments to the command on the constructor.
• Use xPathString field in toJsonString method - utilize instance fields for better encapsulation.
• Safe delete xPathString parameter from toJsonString method - remove unused parameters to clean up the method signature.
• Add Element parameter to DocumentElement constructor - ensure all necessary data is provided at instantiation.
• Use element field in toJsonString method - utilize instance fields for better encapsulation.
• Safe delete element parameter from toJsonString method - further clean up the method signature.
• Introduce field jsonString to store the result of toJsonString method - maintain state within the command object.
• Introduce field elementName to store the element name - move the function state into the command object.
• Introduce field attributes to store the element attributes - move the function state into the command object.
• Introduce field title to store the element title - move the function state into the command object.
• Introduce field file to store the element filename - move the function state into the command object.
• Extract method processDocAttributes in DocumentElement class - break down toJsonString methods into smaller pieces.
• Extract method addStateClosed in DocumentElement class - compose method to handle state closing logic.
• Extract method closeElement in DocumentElement class - compose method to handle element closing logic.
• Extract method processFolderAttributes in DocumentElement class - break down toJsonString methods into smaller pieces.

Replace Conditional with Polymorphism

Replace Conditional with Polymorphism uses polymorphism to handle conditional logic.

• Extract method processElement() in DocumentElement class - extract conditional statement into its own method.
• Encapsulate variable elementName - self-encapsulate the type code.
• Replace Constructor with Factory Function aka Replace Constructor with Factory Method - use factory methods to create an instance of DocumentElement.
• Create DocElement subclass and add selector logic for doc type code value in the factory method.
• Override the type code getter in DocElement class to return the literal type code value.
• Create FolderElement subclass and add selector logic for folder type code value in the factory method.
• Override the type code getter in FolderElement class to return the literal type code.
• Remove type code field elementName from DocumentElement class.
• Add default branch in the factory method to handle unexpected type code values.
• Make getElementName an abstract method and DocumentElement an abstract class.
• Override processElement method in DocElement class. Copy the relevant logic from the conditional statement.
• Push Down Method processDocAttributes to DocElement class - move method to the subclass where it's relevant.
• Rename processDocAttributes method in DocElement class to processAttributes - generalize method name for better readability.
• Push Down Method addStateClosed to DocElement class - move method to the subclass where it's relevant.
• Push Down Method hasChildren to DocElement class - move method to the subclass where it's relevant.
• Override processElement method in FolderElement class. Copy the relevant logic from the conditional statement.
• Push Down Method processFolderAttributes to FolderElement class - move method to the subclass where it's relevant.
• Rename processFolderAttributes method in FolderElement class to processAttributes - generalize method name for better readability.
• Declare processElement method in DocumentElement class as abstract - enforce implementation in subclasses.
• Safe delete getElementName method from DocumentElement class and its subclasses - clean up unused methods.