I have Engineer which looks not very good. Could you point me, how can I make him better organized? Share with me some best practices!

Here is interface:

public interface Engineer {
    String HOMELESS = "homeless";
    String ENGINEER = "engineer";
    String SOFTWARE_ENGINEER = "softwareEngineer";
    String TEST_ENGINEER = "testEngineer";
    String TEST_AUTOMATION_ENIGNEER = "testAutomationEngineer";

    static final int WORK = 1;
    static final int LOOKING_FOR_NEW_JOB = 2;
    static final int BUSY = 3;
    static final int FREE = 4;
    static final int SLEEP = 5;

    boolean isHappy();
    String getEmployer();
    String getType();

    String makeOffer(int salary, String employer);

    void fire();
    void setView(EngineerImpl.View view);
    /**
     * Sets employer
     * @param name
     * @return
     */
    void setEmployer(String name);
    String getName();
    void startWork(long time);

    /**
     * Stops {@link Engineer}
     * @return
     */
    int stopWork(long time);

    /**
     * Sets {@link Engineer} into hibernate mode for {@code seconds}
     * @param seconds
     */
    void sleep(int seconds);
    boolean eatPizza(int pieces);    
}

here is implementation:

public class EngineerImpl implements Engineer {

    private View view;

    static class EngineersFactory {
        public static Engineer getEngineer(String name, String type) {
            return new EngineerImpl(name, type);
        }

        public static Engineer getEngineer(String name) {
            return getEngineer(name, ENGINEER);
        }

        public static Engineer getSoftwareEngineer(String name) {
            return getEngineer(name, SOFTWARE_ENGINEER);
        }

        public static Engineer getTestEngineer(String name) {
            return getEngineer(name, TEST_ENGINEER);
        }

        public static Engineer getTestAutomationEngineer(String name) {
            return getEngineer(name, TEST_AUTOMATION_ENIGNEER);
        }
    }

    interface View {
        void showSmile();
    }

    private boolean isHappy = false;
    private String employer;
    private int salary;
    private String name;
    private int status;
    private long workStartedAt;
    private int previousStatus;
    private final String type;

    public EngineerImpl(String name, String type) {
        isHappy = true;
        this.name = name;
        status = WORK;
        this.type = type;
    }

    @Override
    public String getType() {
        return type;
    }

    @Override
    public void setView(View view) {
        this.view = view;
    }

    @Override
    public boolean isHappy() {
        return isHappy;
    }

    @Override
    public String getEmployer() {
        return employer;
    }

    @Override
    public String makeOffer(int salary, String employer) {
        if (shouldIAcceptNewOffer(salary, employer)) {
            acceptOffer(salary, employer);
            return employer;
        }
        return this.employer;
    }

    @Override
    public void fire() {
        this.salary = 0;
        this.employer = HOMELESS;
        isHappy = false;
        status = LOOKING_FOR_NEW_JOB;
    }

    @Override
    public void setEmployer(String name) {
        this.employer = name;
    }

    @Override
    public String getName() {
        return name;
    }

    @Override
    public void startWork(long time) {
        status = BUSY;
        workStartedAt = time;
    }

    @Override
    public int stopWork(long time) {
        status = FREE;
        view.showSmile();
        return (int) (time - workStartedAt);
    }

    @Override
    public void sleep(int seconds) {
        previousStatus = status;
        status = SLEEP;
        try {
            Thread.sleep(seconds);
        } catch (InterruptedException e) {
            // ...
        }
        status = previousStatus;
    }

    @Override
    public boolean eatPizza(int pieces) {
        isHappy = ((pieces % 2) == 0 && status == FREE);
        if (isHappy) {
            view.showSmile();
        } else {
            sleep(10);
        }
        return isHappy;
    }

    @Override
    public boolean equals(Object engineer) {
        if (this == engineer) {
            return true;
        }
        Engineer e = (Engineer) engineer;
        return this.isHappy == e.isHappy() && hashCode() == e.hashCode();
    }

    @Override
    public int hashCode() {
        return getName().hashCode()
                + getEmployer().hashCode()
                + getType().hashCode();
    }

    private boolean shouldIAcceptNewOffer(int salary, String employer) {
        return salary > this.salary && employer.equals(this.employer);
    }

    private void acceptOffer(int salary, String employer) {
        this.salary = salary;
        this.employer = employer;
        isHappy = true;
        view.showSmile();
    }
}

Some explicit questions:

1. Is it OK to put constants to interface and use them in implementation?
2. Should I make constants static final if they are defined in interface? Which constants should I prefer, int or String?
3. Can I make some additional actions in setter's?
4. When should I write JavaDoc?

Please, keep in mind that I will use this review to refer.