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Polymorphism.java RUNNABLE

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abstract class Shape {
  abstract double area();
  void describe() {
    System.out.println("Area = " + area());
  }
}

class Circle extends Shape {
  double r;
  Circle(double r) { this.r = r; }
  double area() { return Math.PI * r * r; }
}

// Same call → different result. That's polymorphism.
Shape s = new Circle(7.0);
s.describe();   // Area = 153.93

Run → Area = 153.93804002589985 OOP · Topic 4 of 16

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Stop copying codeyou don't understand.

Three on-ramps.

From Hello World to JVM internals

Data structures that stick

From LLMs to production agents

Pick your forge.

Every tutorial, three layers.

Plain-English analogy

Real code, with context

The interview question

Get new tutorials in your inbox.

Stop copying code
you don't understand.