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Concept · Core

Polymorphism

One call, many forms: the SAME method name resolves to different behaviour depending on the actual object — decided at runtime.

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step 1 / 11
1/2One interface, many implementations
«interface»
Shape
+ area(): double
Circle
- r: double
+ area()
Square
- s: double
+ area()
Triangle
- b, h
+ area()
One interface, many implementations
 1interface Shape { double area(); }
 2 
 3class Circle   implements Shape { double area(){ return PI*r*r; } }
 4class Square   implements Shape { double area(){ return s*s; } }
 5class Triangle implements Shape { double area(){ return b*h/2; } }
State
contractarea(): double
✦

A supertype declares the contract: every Shape promises an area() method — but says nothing about HOW.