Minimize mutability
Immutable objects are your safest friend in Java. When fields don’t change after creation, reasoning about the code becomes predictable, thread-safe, and bug-resistant. Make fields private and final, provide no setters, and avoid exposing internal references that could be modified. Prefer final classes unless inheritance is truly needed.
Instead of this mutable class:
public class User {
private String name;
private int age;
public void setName(String name) { this.name = name; }
public void setAge(int age) { this.age = age; }
}Use a Java record to make it immutable and concise:
public record User(String name, int age) { }This automatically makes fields private and final, generates a constructor, and provides getter methods (name() and age()) without setters. The object cannot be modified after creation.
Practical rules:
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Use immutable collections or wrap them in
Collections.unmodifiableList. -
Avoid setters unless there’s a compelling reason.
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Prefer constructing new objects over modifying existing ones.
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Consider records for simple data carriers - they are immutable by default and reduce boilerplate.
Every commit should ask: “Could this object be modified unexpectedly elsewhere?” If yes, rethink its design. Minimizing mutability makes code safer, easier to reason about, and reduces subtle bugs that even experienced developers stumble upon.