Let's get this sorted out—you're right that most searches fixate on tabs vs spaces, but the issue here is about the Tab key's behavior when your cursor isn't at the start of the line. Here's what you need to check:

Step 1: Verify the Smart Insert Mode setting #

The option you already checked (Tab key adjusts the indentation of the current line) works hand-in-hand with Smart Insert Mode to handle indentation anywhere in the line:

1. Open Window > Preferences
2. Navigate to Java > Editor > Typing
3. At the top of the page, make sure Smart Insert Mode is checked. This mode lets Eclipse intelligently adjust indentation instead of just inserting a tab character when you press Tab mid-line or at the end.

Step 2: Align Indentation and Tab Sizes #

Mismatched settings here can cause unexpected behavior:

1. Go to Java > Editor > Indentation
2. Ensure:
   • Indentation size and Tab size are set to the same value (e.g., 4 is standard)
   • Your Tab policy is set to either Spaces only or Mixed (stick with Spaces only if you want to avoid tab characters entirely)

Step 3: Check for Plugin Conflicts #

If you have third-party code editing plugins (like CodeMix, Spring Tools Suite extensions, or custom formatters) installed, they might override Eclipse's default Tab behavior. Try temporarily disabling these plugins and testing the Tab key again to rule out conflicts.

Quick Workaround (If Settings Don't Stick) #

If you need an immediate fix while troubleshooting, use Eclipse's built-in shortcut Ctrl+I—this will adjust the indentation of the current line regardless of where your cursor is positioned.

内容的提问来源于stack exchange，提问作者Cassie