Perhaps you pressed the insert key, which will change the Eclipse editor to Overwrite , and not to Smart Insert (see the information panel at the bottom of the editor) and change the cursor to a block, not a vertical line?
Update : Thanks for the clarification - see mikej's answer, which is correct. I will leave this answer if someone has a similar, related issue that I am describing.
DNA Mar 05 2018-12-12T00: 00Z
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