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Java Fundamentals · Object-Oriented Programming · Lesson 19 of 22

Classes and Objects

Concept

Classes and Objects

A class is a blueprint describing fields (data) and methods (behavior). An object is a specific instance created from that class with the new keyword.

By the end of this lesson
  • Explain the core idea behind Classes and Objects.
  • 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. 1. Read one concept.
  2. 2. Change the example.
  3. 3. Run, compare, and explain.
  4. 4. Complete the challenge below.
ExampleRunnable
class Student {
    String name;
    int age;
}

Student s = new Student();
s.name = "Alex";
System.out.println(s.name);
Try it Yourself »
Self-check before continuing

Without looking at the example, describe what changes when you modify one input in Classes and Objects. 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

Define a Course class with title and level fields, then create one instance.

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Console

Output will appear here...