Records

For decades, a simple Java class that just held a few values meant pages of boilerplate — fields, a constructor, getters, equals , hashCode , toString . Records (Java 16+) collapse all of that into a single line, giving you immutable, correct data classes for free.

Learn Records in our free Java course — a beginner-friendly interactive lesson with worked examples, a practice exercise and a quick reference.

Part of the free Java course at LearnCodingFast — hands-on lessons with examples you run in your browser, plus practice exercises and a quick quiz.

You should know classes, constructors, and fields , and have met equals and hashCode — records generate both for you, so seeing the manual version first makes the magic obvious.

💡 Analogy: Writing a data class the old way is like filling in a long form by hand — name field, address field, signature, witness — for every single document. A record is a pre-filled template: you state the fields once on the dotted line ( record Point(int x, int y) ) and the rest — constructor, accessors, equality, printing — is stamped in automatically. Less to write, nothing to get wrong.

The components you list in the parentheses are the record's whole identity. Two records are .equals() when their components are equal — value-based, not reference-based — which is exactly what you want for data.

A record declaration lists its components in parentheses. From that one line Java generates: private final fields, a canonical constructor, an accessor per component, and equals / hashCode / toString .

To appreciate records, look at what you'd otherwise hand-write — and have to keep in sync every time you add a field. A record does all of this, correctly, in one line.

Records aren't just dumb holders. A compact constructor lets you validate or normalise inputs — note it has no parameter list and no field assignments ; you only write the checks, and Java assigns the fields afterwards.

You can also add normal methods, derived values, static factory methods, and implement interfaces (including Comparable ). What you can't do: add extra instance fields or extend another class.

Records shine with the rest of modern Java. Because each component has a clean accessor, method references like Product::price plug straight into a Comparator . This is the combination you'll meet again in the checkpoint.

These lines declare a record with a compact constructor and use it. Put them in the right order.

Open the record header, open the compact constructor (no parameter list!), add the validation, close the constructor, close the record, then use it.

Predict the output before opening each answer.

Answer: true Coord[x=1, y=2] . Records get value-based equals for free, so two coords with the same components are equal, and the generated toString prints the component names and values.

Answer: No. A record component becomes a private final field with no setter, so u.name = "Bob" fails to compile ( cannot assign a value to final variable name , and the field isn't accessible anyway). Records are immutable — to "change" one, create a new instance.

Answer: C — m.cents() . The accessor is named after the component with no "get" prefix and is a method call, so m.getCents() doesn't exist and m.cents (the field) is private.

🎯 Your Turn #1 — Declare a record

Write a one-line Book record with the right components so the main method compiles.

🎯 Your Turn #2 — Validate with a compact constructor

Add a compact constructor that rejects a negative quantity.

🧩 Mini-Challenge — Contact book

Model contacts with a record, then sort and print them with aligned columns.

You can now declare records, know exactly what they generate, why they're immutable and value-based, how to validate with a compact constructor, and how to add your own methods. You've replaced pages of error-prone boilerplate with a single, correct line.

Next up: Regular Expressions — matching and extracting text patterns with Pattern and Matcher.

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