Temporary Field

Symptom

A class field used by only one method, set to null or default the rest of the time.

Goal

The temporary state moves to a dedicated class that exists only when it's relevant.

Smellier version

class Order {
  shippingTrack = null;
  ship() {
    this.shippingTrack = computeTrack();
  }
}

Fresher version

class Order    { ship() { return new Shipment(this); } }
class Shipment { /* owns the track */ }

Savings

Null-checks vanish; class invariants tighten; the new class has a clear purpose.

Note

Reader must trace the conditions under which the field is meaningful; null-checks scatter; the field's role is unclear.