public final class HealthDataType

A kind of health data – steps, heart rate, sleep, body mass. Instances are interned constants, so == is a valid identity test.

Why this is not an enum

Three reasons, in order of how much trouble each would cause:

1. Each constant carries a HealthUnit, and a Java enum constructor that references another class’s statics is an initialization-order hazard – the unit would be null for whichever class loaded first.
2. forId(String) has to be total across framework versions. An app that persisted "vo2Max" and is later restored by an older runtime must get null, not the IllegalArgumentException that Enum.valueOf throws.
3. Ports need to attach platform metadata to types without the core knowing about it.

There is no custom type

Deliberately no HealthDataType.custom(String). A custom type would have no canonical unit, no aggregation style and no cross-platform mapping – an untyped string passthrough that works on exactly one platform, which is the failure mode this API exists to prevent. Adding a type is a change to this class.

Permissions are declared, not inferred

The build server cannot see which of these constants an app touches: constant references compile to field reads, and the class scanner only records type and method references. Android’s per-type android.permission.health.* set therefore comes from the android.health.read and android.health.write build hints, which use the getId() values below as tokens. This also matches Google Play policy, which requires declaring exactly the data types you use.