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The Java Interview Handbook: 300+ Interview Questions

Designing Classes

Explore how to design Java classes effectively by understanding best practices in overriding equals and hashCode methods, managing immutability, cloning, encapsulation, and using nested classes. This lesson helps you write safer, cleaner, and more maintainable classes in Java.

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Notes on Class Design

  1. Avoid finalizers as they slow down performance and run non-deterministically or may never run at all. Use try-with-resources or try-with-finally to ensure code cleanup.

  2. Overriding equals() method should honour the following properties:

    • Reflexivity: x.equals(x) == true

    • Symmetric: x.equals(y) == y.equals(x)

    • Transitivity: x.equals(y) == y.equals(z) == z.equals(x)

    • Consistent: x.equals(y) == x.equals(y) == x.equals(y) == ...

    • Non-nullity: x.equals(null) should equal false

  3. Always override hashCode() when you override equals()

  4. Overriding hashCode() should honor the following properties:

    • Invoking hashCode() on the same object should always return the same integer.

    • If there are two objects x and y and x.equal(y) then x.hashCode() == y.hashCode().

    • On the contray if x ...