I was reading Planck's postulate the other day on Wikipedia and couldn't help but noticing the sentence:
"...is the postulate that the energy of oscillators in a black body is quantized..."
And a black body is nothing but a theoretic object that absorbs all energy and emits nothing back (i.e. a black hole)
This causes a conflict in my understanding because I know that aside from energy, many other things are also quantized i.e. angular momentum. But I would have never assumed that quantization only exists for a black body.
Can someone resolve this conflict? Is a black body the only thing that exhibits the phenomenon of quantization or is quantization everywhere in nature?