ij-osx-decompose-conditional.md

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JetBrains IntelliJ IDEA on Mac OS X

Kata: Decompose Conditional

The decompose conditional refactoring is used to simplify a long series of if/else blocks and/or switch blocks. This usually improves readability, and often has the side benefit of making duplicate code more obvious, when duplication hides in the repetitious blocks of code.

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)
• ⇧ and ↓ (Shift) with (Down Arrow) - select lines
• ⌘⌥M (Command + Option + M) - open the "extract method" dialog

Keystrokes without explanations

⌃⇥
⌘↖︎ (or fn⌘←)
⌘L 10
hold ⇧
↓    <= 20 times
↓
↓
↓
↓
↓
↓
↓
↓
↓
↓
↓
↓
↓
↓
↓
↓
↓
↓
↓
release ⇧
⌘⌥M
⇥
validateArguments
⏎
⌘L 12
hold ⇧
↓    <= 19 times
↓
↓
↓
↓
↓
↓
↓
↓
↓
↓
↓
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↓
↓
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release ⇧
⌘⌥M
⏎
←
⏎
⏎
⌘L 21
hold ⇧
↓    <= 19 times
↓
↓
↓
↓
↓
↓
↓
release ⇧
⌘⌥M
⇥
valueForRange
⏎
hold ⌃
⇥
release ⌃
⏎

Reverse the changes:

⌘Z (Command + Z) repeatedly.

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 10. (This should be a line that reads, "int errorCount = 0;").
5. Hold ⇧(Shift) and press ↓(Down Arrow) 20 times to select the if/else block that starts on line 10 (through line 29).
6. Press ⌘⌥M (Command + Option +M) to open the "extract method" dialog.
7. In the "extract method" dialog, select:

• Visibility: leave as private
• Name: change to validateArguments
• Arguments: leave as presented

1. Press ⏎ (Return/Enter) to apply the refactoring.
2. Press ⌘L (Command + L) to open the "goto line number" dialog. Navigate to line 12. (This should be a line that reads, "if (intArg >= 0 && intArg < 10) {").
3. Hold ⇧(Shift) and press ↓(Down Arrow) 19 times to select the if/else block that starts on line 12 (through line 30).
4. Press ⌘⌥M (Command + Option +M) to open the "extract method" dialog.
5. In the "extract method" dialog, select:

• Visibility: leave as private
• Name: leave as presented
• Arguments: leave as presented

1. Press ⏎ (Return/Enter) to apply the refactoring.
2. IntelliJ displays a dialog for "No exact method duplicates were found" and offers the option to keep the original signature or accept the changed signature. Press ← (Left Arrow) to highlight keep original signature and press ⏎ (Return/Enter) to select that option.
3. IntelliJ displays a dialog offering to replace the near-duplicate code. Press ⏎ (Return/Enter) to accept the suggestion.
4. At this point there is near-duplicate code inside the extracted getString() method.
5. Press ⌘L (Command + L) to open the "goto line number" dialog. Navigate to line 21. (This should be a line that reads, "if (intArg >= 0 && intArg < 10) {").
6. Hold ⇧(Shift) and press ↓(Down Arrow) 7 times to select the if/else block that starts on line 21 (through line 27).
7. Press ⌘⌥M (Command + Option +M) to open the "extract method" dialog.
8. In the "extract method" dialog, select:

• Visibility: leave as private
• Name: change to valueForRange
• Arguments: leave as presented

1. Press ⏎ (Return/Enter) to apply the refactoring.
2. IntelliJ displays a drop-down message entitled "Process Duplicates," with the message "IDEA has detected 1 code fragment," etc.
3. The default selection is "No." Press ⌃⇥ (Ctrl + Tab) to move the cursor to "Yes."
4. Press ⏎ (Return/Enter) to accept the suggestion.

To reverse the changes:

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