Let us consider the following example:
main class HelloWorld {
component Button bt{text=="Hello World!"};
}
This program has only one component declaration which declares that
the panel has a button named bt and the text on the button is
"Hello World!". The statement in the brackets after bt is called
a constraint that constrains the value of the text attribute of
bt. Nothing is said about the color and size of the button, the
font of the text, and the position of the button in the panel. we can
but do not have to give the values to these attributes. The system
will determine the attribute values for us either by using the
constraints we provided or by using the default values.