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Top => IntelliJ IDEA on Mac OS X

JetBrains IntelliJ IDEA on Mac OS X

Kata: Extract method 1

The extract method refactoring takes a block of inline code and re-casts it as a method in the same class, replacing the inline code with a method call. Even if there is no duplication, it can be useful to extract chunks of code out of a long method to make the code more readable and easier to isolate.

Extract method is often used to reduce duplication by consolidating identical or very similar inline code snippets into a single method. It is also a building block for multi-steps refactorings such as decompose conditional and compose method.

Key sequences to practice

  • ⌃⇥ (Ctrl + Tab) - navigate from the project view pane to an editor pane

  • ⌘↖︎ (Command + Home) or fn⌘← (Fn + Command + Left Arrow) - navigate to the top of the file (in editor)

  • ⌥→ (Option + Right Arrow) - move forward by token (word)

  • ⌥⇧→ (Option + Shift + Right Arrow) - move forward by token (word) selecting as you go

  • ⌘C (Command + C) - select current line (when nothing is selected)

  • ⌃↓ (Ctrl + Down Arrow) - move through the file method by method

  • ⌥→ (Option + Right Arrow) - move through the file token (word) by token

  • ↘︎ (End) or fn→ (Fn + Right Arrow) - move the caret to the end of the current line.

  • → (Right Arrow) - move the caret one position to the right

  • ⌘⌥⇧] (Command + Option + Shift + ]) - select from caret through end of block

  • ⇧ and ↓ (Shift) with (Down Arrow) - select lines

  • ⌘⌥M (Command + Option + M) - open the "extract method" dialog

Keystrokes without explanations

⌃⇥
⌘↖︎ (or fn⌘←)
⌘L 32
⌥→
⌥→
⌥→
⌥⇧→
⌥⇧→
⌥⇧→
⌥⇧→
⌥⇧→
⌥⇧→
⌥⇧→
hold ⇧
→
release ⇧
⌘⌥M
Visibility: Public
Name: isABC
Arguments: stringArg
OK

Walkthrough of steps with explanations

  1. Open the Java source file, LongConditional.java.
  2. If focus is not already in the editor pane for LongConditional.java, press ⌃⇥ (Ctrl + Tab) and select the editor pane for LongConditional.java.
  3. Press ⌘↖︎ (Command + Home) or fn⌘← (Fn + Command + Left Arrow) to place the caret at the top of the file.
  4. Press ⌘L (Command + L) to open the "goto line number" dialog. Navigate to line 32. (This should be a line that reads, "if (stringArg.matches("^ABC.*?")) {").
  5. Press ⌥→ (Option + Right Arrow) three times. The caret should now be at the "s" in "stringArg".
  6. Press ⌥⇧→ (Option + Shift + RightArrow) seven times, to select this text: "stringArg.matches("^ABC.*?"". Note that if you press it one more time, it will select both the closing parentheses, and we only want the first one.
  7. Hold ⇧ (Shift) and press → (Right Arrow) once to extend the selection so that the first closing parenthesis is included.
  8. Press ⌘⌥M (Command + Option +M) to open the "extract method" dialog.
  9. In the "extract method" dialog, select:
  • Visibility: Public
  • Name: isABC
  • Arguments: stringArg

The editor will detect addtional code fragments that match the selection, and will prompt you to review and replace them. Choose "Replace" for each one.

To reverse the changes:

  1. Press ⌘Z (Command + Z) repeatedly until the changes have been reversed.