Converting if/else chains to ternary operator in IntelliJ IDEA (if/else if/else)

Question

Why doesn't IntelliJ IDEA convert an if/else chain like:

int x;
if (true) x = 5;
else if (false) x = 7;
else x = 9;

into the equivalent ternary expression:

int x = true ? 5 :
        false ? 7 :
         9;

Even though the inspection says it supports if/else chains?

Answer

IntelliJ IDEA's default behavior does not support converting an entire if/else chain to a ternary operator. For chains involving more than two outcomes, such as multiple if/else statements, a ternary conversion is not implemented directly. However, if you need a ternary operator to replace your if/else chain, especially in cases like:

int x = (color(sky) == blue) ? 5 :
        (temp(sun) == hot) ? 7 : 
         9;

where conertion to ternary or switch expressions are not applicable, you can create a custom inspection in IntelliJ IDEA to achieve this.

Steps to Enable Custom Inspection for Ternary Conversion:

1. Open the Settings: Go to Settings/Preferences and navigate to Editor | Inspections.

2. Add a Custom Inspection:

   • Click Add Custom Inspections.
   • Select Add Structural Replace Inspection.
   • In the top-right corner, set the language to Java.

3. Define the Search Template: Copy and paste the following template as the Search template:

   $Type$ $var$;
   if ($Condition1$) $var$ = $ThenStatement$;
   else if ($Condition2$) $var$ = $ElseStatement1$;
   else $var$ = $ElseStatement2$;
   

4. Define the Replace Template: Copy and paste the following for the Replace template:

   $Type$ $var$ = $Condition1$ ? $ThenStatement$ :
           $Condition2$ ? $ElseStatement1$ :
                   $ElseStatement2$;
   

5. Save Inspection:

   • Click OK to save the structural pattern.
   • Click OK again in the Inspections window to apply the settings.

6. Apply the Inspection: Go to your code, place your caret at the int x; line, press option+Enter (Mac), Alt+Enter(Windows), and IntelliJ should suggest a replacement with the ternary operator.

By following these steps, you can enable the ternary replacement for if/else chains as per your needs.

Reference

https://www.jetbrains.com/help/idea/regex-search-and-replace-inspections.html