Incompatible type for <thing>. Can't convert <type> to <other type>

You have provided an item of data that wasn't of the type expected, and Java isn't aware of a way to convert between them (although there might be). If you are being told what looks like a char is a String, then see "<char>" Vs '<char>'.

String foo = new String("bar");

boolean bob = foo.startsWith(5);  The startsWith method needs a String, not an int

Code that would work:
boolean bob = foo.startsWith("5");
or
boolean bob = foo.startsWith("b");

Check any parameters you're passing are of the right type. For example, the method doStuff(short foo) wouldn't work if you passed a String.