Check out example codes for "sql developer sql worksheet not showing". It will help you in understanding the concepts better.

Code Example 1

I was able to solve this by :

Closing SQL developer
Deleting the file SqlHistory.xml that is located at C:\Users\AppData\Roaming\SQL Developer\. Alternatively, you can rename it to e.g SqlHistoryOLD.xml
Now when you open SQL developer and create a new SQL worksheet, it will work :)

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