Builder: required fields in the constructor, optional in setters

Not every builder needs a separate Builder class: putting the fields that must always be supplied in the constructor, and letting chained setters fill in the rest, still forces callers to provide the essentials while keeping the optional ones fluent.

Code

class Coordinate {
    private final double lat, lon;
    private String label = "unnamed";
    Coordinate(double lat, double lon) { this.lat = lat; this.lon = lon; }
    Coordinate label(String l) { label = l; return this; }
    public String toString() { return label + " (" + lat + ", " + lon + ")"; }
}
Coordinate point = new Coordinate(12.9, 77.6).label("Office");
System.out.println(point);

Output

Office (12.9, 77.6)