What is need History.fireCurrentHistoryState() in GWT History?

Hello I am working on a GWT sample history management application. Here is my onModuleLoad Code.

public void onModuleLoad() {
    ContentPanel panel = ContentPanel.getInstance();
    if(History.getToken()!=null && History.getToken().length()==0)
    {
        History.newItem("first_page");
    }
    History.addValueChangeHandler(new HistoryHandler());
    RootPanel.get().add(panel);
    History.fireCurrentHistoryState();
}

In this I fired History.fireCurrentHistoryState(); to fire current state of history. Now In my firstPanel class ther is button named Second Panel on which history token second_page is fired.

public FirstPanel() {
    VerticalPanel panel = new VerticalPanel();
    Button button2 = new Button("Second Panel");
    button2.addClickHandl开发者_如何学Pythoner(new ClickHandler() {
        public void onClick(ClickEvent event) {
            History.newItem("second_page");
        }
    });
    panel.add(button2);
    initWidget(panel);
}

But here no need to fire History.fireCurrentHistoryState() ; again. simply histtory.newItem works fine.

Now I want to know that what the need of History.fireCurrentHistoryState() at module load time only? Also why it is not required second time in the application.?

History.fireCurrentHistoryState() invokes your history handlers without actually inserting new history item in browser history stack, while History.newItem(token) does insert new history token into history stack.

Note: if your current token is the same as new token (i.e. same page is reloaded), then browsers do not insert this into history stack. In this case (current token == new token) History.fireCurrentHistoryState() has the same effect as History.newItem(currentToken).