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.