Question

I have the following abstract class

public abstract class ReturnAgentFromTab extends BasePage{

    @Persist("session")
    public abstract Agent getAgent();
    public abstract void setAgent(Agent agent);

    @InjectObject("spring:agentApplicationModeResolver")
    public abstract AgentApplicationModeResolver getAgentApplicationModeResolver();

    .... more @InjectObject()

    public void nextPage(IRequestCycle cycle) {

        setApplicationModeUsingAgentStatus(getAgent());

        AgentSearchNavigationManager navManager = getAgentSearchNavigationManagerFactory().getAgentSearchNavigationManager();
        FlowStage stage = getFlowStage();
        if (stage == null) {
            setApplicationModeUsingAgentStatus(getAgent());
            stage = getUserDefaultFlowStageService().getDefaultFlowStage(UserHolder.getUser(), getVisitClass().getApplicationMode());
        }

        Class nextPageClass = navManager.getNextPage(getUserDefaultFlowStageService());

        String nextPageQualifier = getUserDefaultFlowStageService().getPageQualifier(getAgent(), nextPageClass, getVisitClass().getApplicationMode());
        IPage nextPage = getPageUtils().getPage(nextPageClass, nextPageQualifier);
        if ((getFlowStage() instanceof PSDFlowStage)) {
            nextPageQualifier = getFlowStage().getValue();
        }
        nextPage = getPageUtils().getPage(nextPageClass, nextPageQualifier);
        if (navManager instanceof NameBasedAgentSearchNavigationManager && nextPageClass != SignOffStatusPage.class) {
            NameBasedAgentSearchNavigationManager nameBasedNavManager = (NameBasedAgentSearchNavigationManager) navManager;
            String nextPageName = nameBasedNavManager.getNextPageName(stage); 
            if (!nextPageName.equals(nextPageClass.getSimpleName())) {
                nextPage = getPageUtils().getPage(nextPageName, nextPageQualifier);
            }
        }

        if (isNextPageActivateAgentGeneral(nextPage)) {
            initialisePageLink(nextPageClass, nextPage);
        }
        ((WuamsBasePage) nextPage).init(getAgent().getAgentId());
        getPageUtils().navigateTo(nextPage);

    }

    private void setApplicationModeUsingAgentStatus(Agent agent) {
        getVisitClass().setApplicationMode(getHomeLinksFactory().getRegionHomeLinksService().getApplicationMode(agent));
    }

    private boolean isNextPageActivateAgentGeneral(IPage nextPage) {
        return nextPage instanceof ActiveAgentGeneralPage;
    }

    private void initialisePageLink(Class nextPageClass, IPage nextPage) {
        if (getVisitClass().getPageLink() == null) {
            getVisitClass().setPageLink(PageLinkUtil.getPageLinkMessageKeyFromPageClass(nextPageClass, 
                    getUserDefaultFlowStageService().getDefaultFlowStage(UserHolder.getUser(), getVisitClass().getApplicationMode()).getValue()));
        }
    }

}

What I want to do is call my nextPage(cycle) from another class that is abstract and extends ReturnAgentFromTab, but when I try

public abstract class DoSomethingWithAgent extends ReturnAgentFromTab {

@Persist("session")
public abstract ReturnAgentFromTab getReturnAgentFromTab();
public abstract void setReturnAgentFromTab(ReturnAgentFromTab returnAgentFromTab);
....
getReturnAgentFromTab().nextPage(cycle);

I get a null pointer exception, I know this is because I am not actually setting ReturnAgentFromTab anywhere but I do not understand how to set it using abstract classes. Can anybody help?

If ye need more code just ask

Answer 1

The point of abstract classes is to simply not implement certain things, such as providing certain objects. The method getReturnAgentFromTab() is a perfect example: the class itself does not care where that object comes from because that is the sole responsibility of the subclass. So extend that class, write that method, and all of a sudden the base class does its thing.