We can use DefaultTableModel.setRowCount(int) for this purpose, refering to Java's Documentation:
public void setRowCount(int rowCount)
Sets the number of rows in the model. If the new size is greater than
the current size, new rows are added to the end of the model If the
new size is less than the current size, all rows at index rowCount
and greater are discarded.
This means, we can clear a table like this:
DefaultTableModel dtm = (DefaultTableModel) jtMyTable.getModel();
dtm.setRowCount(0);
Now, on "how does java discard those rows?", I believe it just calls some C-like free(void*) ultimately somewhen, or maybe it just removes all references to that memory zone and leaves it for GC to care about, the documentation isn't quite clear regarding how this function works internally.
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