Working Effectively With Legacy Code
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Michael Feather's Working Effectively with Legacy Code presentation for Agile India User Groups in Bangalore, Delhi and Mumbai
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Working Effectively With Legacy Code
- 1. Working Effectively with Legacy Code Michael Feathers [email_address]
- 4. Let’s Try It
- 5. PageGenerator::generate() std::string PageGenerator::generate() { std::vector<Result> results = database.queryResults(beginDate, endDate); std::string pageText; pageText += "<html>"; pageText += "<head>"; pageText += "<title>"; pageText += "Quarterly Report"; pageText += "</title>"; pageText += "</head>"; pageText += "<body>"; pageText += "<h1>"; pageText += "Quarterly Report"; pageText += "</h1><table>"; …
- 6. Continued.. … if (results.size() != 0) { pageText += "<table border=amp;quot;1amp;quot;>"; for (std::vector<Result>::iterator it = results.begin(); it != results.end(); ++it) { pageText += "<tr border=amp;quot;1amp;quot;>"; pageText += "<td>" + it->department + "</td>"; pageText += "<td>" + it->manager + "</td>"; char buffer [128]; sprintf(buffer, "<td>$%d</td>", it->netProfit / 100); pageText += std::string(buffer); sprintf(buffer, "<td>$%d</td>", it->operatingExpense / 100); pageText += std::string(buffer); pageText += "</tr>"; } pageText += "</table>"; } else { …
- 7. Continued.. … pageText += "<p>No results for this period</p>"; } pageText += "</body>"; pageText += "</html>"; return pageText; } // Argh!!
- 16. (told you) public class AccountDetailFrame extends Frame implements ActionListener, WindowListener { private TextField display = new TextField(10); … private AccountDetailFrame(…) { … } public void performAction(ActionEvent event) { String source = (String)event.getActionCommand(); if (source.equals(“project activity”)) { DetailFrame detailDisplay = new DetailFrame(); detailDisplay.setDescription( getDetailText() + “ “ + getProjectText()); detailDisplay.show(); String accountDescription = detailDisplay.getAccountSymbol(); accountDescription += “: “; … display.setText(accountDescription); … } }
- 17. Separate a dependency public class AccountDetailFrame extends Frame implements ActionListener, WindowListener { private TextField display = new TextField(10); … private AccountDetailFrame(…) { … } public void performAction(ActionEvent event) { String source = (String)event.getActionCommand(); if (source.equals(“project activity”)) { DetailFrame detailDisplay = new DetailFrame(); detailDisplay.setDescription( getDetailText() + “ “ + getProjectText()); detailDisplay.show(); String accountDescription = detailDisplay.getAccountSymbol(); accountDescription += “: “; … display.setText(accountDescription); … } }
- 18. After a method extraction.. public class AccountDetailFrame extends Frame implements ActionListener, WindowListener { … public void performAction(ActionEvent event) { performCommand((String)event.getActionCommand()); } void performCommand(String source); if (source.equals(“project activity”)) { DetailFrame detailDisplay = new DetailFrame(); detailDisplay.setDescription( getDetailText() + “ “ + getProjectText()); detailDisplay.show(); String accountDescription = detailDisplay.getAccountSymbol(); accountDescription += “: “; … display.setText(accountDescription); … } }
- 19. More offensive dependencies.. public class AccountDetailFrame extends Frame implements ActionListener, WindowListener { … void performCommand(String source); if (source.equals(“project activity”)) { DetailFrame detailDisplay = new DetailFrame(); detailDisplay.setDescription( getDetailText() + “ “ + getProjectText()); detailDisplay.show(); String accountDescription = detailDisplay.getAccountSymbol(); accountDescription += “: “; … display.setText(accountDescription); … } }
- 20. More refactoring.. public class AccountDetailFrame extends Frame implements ActionListener, WindowListener { private TextField display = new TextField(10); private DetailFrame detailDisplay; … void performCommand(String source); if (source.equals(“project activity”)) { setDescription(getDetailText() + “” + getProjectText()); … String accountDescripton = getAccountSymbol(); accountDescription += “: “; … setDisplayText(accountDescription); … } } …
- 21. The aftermath.. We can subclass and override getAccountSymbol , setDisplayText , and setDescription to sense our work
- 22. A Test.. public void testPerformCommand() { TestingAccountDetailFrame frame = new TestingAccountDetailFrame(); frame.accountSymbol = “SYM”; frame.performCommand(“project activity”); assertEquals(“06 080 012”, frame.getDisplayText()); }
- 33. Breaking Dependencies 0 Extract Interface Extract Implementor
- 41. Breaking Dependencies 1 Parameterize Method Extract and Override Call
- 46. Breaking Dependencies 2 Link-Time Polymorphism
- 47. Link-Time Polymorphism void account_deposit(int amount) { struct Call *call = (struct Call *) calloc(1, sizeof (struct Call)); call->type = ACC_DEPOSIT; call->arg0 = amount; append(g_calls, call); }
- 49. Breaking Dependencies 3 Expose Static Method
- 54. Breaking Dependencies 4 Introduce Instance Delegator
- 58. Dependency Breaking 5 Template Redefinition
- 60. Template Redefinition template<typename SOCKET> class AsyncReceptionPortImpl { private: SOCKET m_socket; Packet m_packet; int m_segmentSize; … public: AsyncReceptionPortImpl(); void Run(); }; typedef AsyncReceptionPortImpl<CSocket> AsyncReceptionPort;
- 62. Writing Tests
- 68. WELC Understanding, Isolating, Testing, and Changing ..Untested Code www.objectmentor.com www.michaelfeathers.com
Editor's Notes
- Notes 2/5/2004 Michael Feathers