Seven Jobs That Throw

interface Job {
    void run();
    void pause();
    void resume();
    void progress(ProgressSink sink);
}

final class VacuumTablesJob implements Job {
    public void run()  { /* 40 minutes of DDL, not interruptible */ }
    public void pause()  { throw new UnsupportedOperationException(); }
    public void resume() { throw new UnsupportedOperationException(); }
    public void progress(ProgressSink s) { /* nothing to report */ }
}

There are 11 implementations of Job. Seven of them throw from pause and resume. The team proposes splitting the interface into Job { run(); progress(); } and PausableJob extends Job { pause(); resume(); }.

Which principle does that split most directly serve, and what disappears first?

Single Responsibility. VacuumTablesJob currently runs DDL and reports progress, and the split gives each resulting class exactly one reason to change.

Interface Segregation. Martin's statement is that many client-specific interfaces beat one general purpose interface; after the split, the scheduler's pause button binds to PausableJob and the seven UnsupportedOperationException stubs get deleted rather than relocated.

Open/Closed. New job types can be added without editing Job, so the interface stops changing every time a job with new capabilities arrives.

Dependency Inversion. The scheduler stops depending on concrete job classes and depends on an abstraction instead, so the concrete jobs become replaceable.