The Diamond Problem
The "diamond problem" (sometimes referred to as the "deadly diamond of death") is an ambiguity that arises when two classes B and C inherit from A, and class D inherits from both B and C. If D calls a method defined in A (and does not override the method), and B and C have overridden that method differently, then from which class does it inherit: B, or C?
For example, in the context of GUI software development, a class Button may inherit from both classes Rectangle (for appearance) and Clickable (for functionality/input handling), and classes Rectangle and Clickable both inherit from the Object class. Now if the equals method is called for a Button object and there is no such method in the Button class but there is an overridden equals method in both Rectangle and Clickable, which method should be eventually called?
It is called the "diamond problem" because of the shape of the class inheritance diagram in this situation. In this article, class A is at the top, both B and C separately beneath it, and D joins the two together at the bottom to form a diamond shape.
Read more about this topic: Multiple Inheritance
Famous quotes containing the words diamond and/or problem:
“Masts in the offing wagged their tops;
The swinging waves pealed on the shore;
The saffron beach, all diamond drops
And beads of surge, prolonged the roar.”
—John Davidson (1857–1909)
“The problem is simply this: no one can feel like CEO of his or her life in the presence of the people who toilet trained her and spanked him when he was naughty. We may have become Masters of the Universe, accustomed to giving life and taking it away, casually ordering people into battle or out of their jobs . . . and yet we may still dirty our diapers at the sound of our mommy’s whimper or our daddy’s growl.”
—Frank Pittman (20th century)