Java Fundamentals · Object-Oriented Programming · Lesson 20 of 22
Constructors and Inheritance
Concept
Constructors and Inheritance
A constructor runs automatically when an object is created, usually to set initial field values. The extends keyword lets one class inherit fields and methods from another.
By the end of this lesson
- Explain the core idea behind Constructors and Inheritance.
- Predict output before running a change.
- Test one realistic and one unusual input.
- Use the result to make the next decision.
How to study this page
- 1. Read one concept.
- 2. Change the example.
- 3. Run, compare, and explain.
- 4. Complete the challenge below.
ExampleRunnable
class Animal {
void speak() { System.out.println("..."); }
}
class Dog extends Animal {
Dog() { System.out.println("A dog was created"); }
void speak() { System.out.println("Woof!"); }
}Self-check before continuing
Without looking at the example, describe what changes when you modify one input in Constructors and Inheritance. Then reopen the editor and prove your explanation with a small test.
You are ready to continue when you can predict, test, and explain the result.
Your turn
Add a constructor to your Course class that sets title when the object is created.
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Console