Records (Java 16+)

Records: data classes without the boilerplate

A record is a restricted class whose primary purpose is carrying immutable data. The declaration is concise:

public record Point(int x, int y) { }

The compiler automatically generates:

• A canonical constructor Point(int x, int y) that assigns all components.
• Accessor methods x() and y() — note: no getX()/getY().
• equals, hashCode, and toString based on all components.

Point p1 = new Point(3, 4);
Point p2 = new Point(3, 4);
System.out.println(p1.x());          // 3 — accessor, not getX()
System.out.println(p1.equals(p2));   // true — value equality
System.out.println(p1);             // Point[x=3, y=4]

Compact canonical constructor — validation

To add validation without duplicating assignment code, use a compact canonical constructor (no parameter list — it inherits the record's parameters):

public record Range(int lo, int hi) {
    Range {                         // compact form — no (int lo, int hi)
        if (lo > hi)
            throw new IllegalArgumentException(lo + " > " + hi);
        // assignment of fields happens automatically after this block
    }
}

What records cannot do

• Records are implicitly final — they cannot be extended.
• Component fields are implicitly private final — they cannot be mutated.
• Records cannot extend another class (they already extend java.lang.Record).
• Records can implement interfaces.