You: Master, I heard this PECS in the JAVA world. But I’m deeply puzzled by it.
Master: Do you know what it stands for?
You: Producer Extends Consumer Super?
Master: In order to understand it, you shall stop thinking about what these words mean, it’s not helpful at all. Just follow my questions.
You: Yes, Master. Please start.
Master: There are plants, then there are fruits, then there are apples and pears. They form a hierarchy.
You: Apples and pears are fruits, and all fruits are also plants. Right?
You: I think there are also plants other than fruits, like grass?
Master: You are right. Keep that in mind for now.
Master: (Pointing at a basket on the table) What is this?
You: A basket.
Master: Correct. Simply a basket. No more no less.
Master: Pay attention to my words now carefully. I tell you now that this is a fruit basket.
You: OK, so it has fruits in it then. What fruits I wonder?
Master: Asorted fruits, not important.
Master: Now I tell you that all fruits are edible.
Master: Answer me. Do you think you can take anything from the basket with you eyes closed, and eat it?
You: Yes, I can.
Master: Now let’s change the setting. If I now tell you that this is a plant basket. Do you think you can still do the above task?
You: No, I may get grass, which is not tasty I guess.
Master: (Still pointing at the basket) Now I tell you this is a fruit basket.
Master: Suppose you have an apple, are you feeling comfortable putting it in the basket?
Master: Suppose you have an pear instead, are you feeling comfortable putting it in the basket?
Master: OK. Now I tell you that this is not a fruits basket, but a plant basket. Are you now feeling comfortable putting you apple or pear in it?
You: Yes, I am. Apples and pears are also plants anyway.
Master: You are right. Now let’s again change the setting. I tell you now that this is a apples basket. And you have a pear in your hand. Are you feeling comfortable putting it in the basket?
You: … Not sure I want to put a pear into a basket that is full of apples.
Master: OK. We are done here.
You: (feeling enlightened)