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Glad to help, and sleep well!

I suggest you do this:

public boolean action(Event e,Object o)
{
if (e.target == bplus)
{
D1 = new Double(t1.getText());
d1 = D1.doubleValue();
D2 = new Double(t2.getText());...

JApplets were included in Swing in Java 1.1 or 1.2 (fuzzy historical references, and I wasn't there).

Applets are AWT (not Swing). Your book should be consistent in the time frame of the material...

If you're trying to run the code you've posted (with the first 'mport' fixed), you should be seeing a red squiggly under this line:

return false;// Here ends the original code. . . . (Line 50 to...