The following new methods on AlphaComposite would simplify a fair amount
of code:

public AlphaComposite derive(float alpha);

public AlphaComposite derive(int rule);

The first one in particular would simplify the creation of new objects from:

AlphaComposite ac = AlphaComposite.getInstance(AlphaComposite.SRC_OVER, 0.5f);

to:

AlphaComposite ac = AlphaComposite.SrcOver.derive(0.5);

this would also simplify a fade operation where a new AlphaComposite needs
to be created with a different alpha parameter for each iteration of the
fade:

ac = ac.derive(newfadeamount);

The latter method that derives a new instance with a new rule is probably
less useful, but is included for completeness.