I have do it but different way. Whole toolbar item is passed via handler. I can share you code:
Forward Editor code:
package handler;
import org.eclipse.core.commands.AbstractHandler;
import org.eclipse.core.commands.ExecutionEvent;
import org.eclipse.core.commands.ExecutionException;
import org.eclipse.ui.IEditorReference;
import org.eclipse.ui.IWorkbenchPage;
import org.eclipse.ui.IWorkbenchWindow;
import org.eclipse.ui.PartInitException;
import org.eclipse.ui.handlers.HandlerUtil;
import rcp_demo.Editor.EmployeeEditor;
import rcp_demo.Editor.EmployeeEditorInput;
import rcp_demo.Editor.EnquiryEditor;
import rcp_demo.Editor.EnquiryEditorInput;
import rcp_demo.Editor.FoodDetailsEditor;
import rcp_demo.Editor.FoodDetailsEditorInput;
import rcp_demo.Editor.StaffdetailsEditor;
import rcp_demo.Editor.StaffdetailsEditorInput;
//Defauklt Editor ID
import rcp_demo.Editor.UserEditor;
import rcp_demo.Editor.UserEditorInput;
/**
 * @author summet
 * 
 */
public class SwitchingHandler extends AbstractHandler {
/*
 * (non-Javadoc)
 * 
 * @see
 * org.eclipse.core.commands.IHandler#execute(org.eclipse.core.commands.
 * ExecutionEvent)
 */
String tempEditorID = null;
@Override
public Object execute(ExecutionEvent event) throws ExecutionException {
    System.out.println("SwitchingHandler command call");
    // TODO Auto-generated method stub
    // HandlerUtil.getActiveWorkbenchWindow
    IWorkbenchWindow window = HandlerUtil.getActiveWorkbenchWindow(event);
    IWorkbenchPage page = window.getActivePage();
    IEditorReference[] editorRefs = page.getEditorReferences();
    // get the editor instance by given id (pEditorId)
    if (page.getActiveEditor() == null || page.getActiveEditor().equals("")) {
        // Default Editor Open via command
        UserEditorInput input = new UserEditorInput();
        try {
            page.openEditor(input, UserEditor.ID);
        } catch (PartInitException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return null;
    } else {
        // First check Temp ID;
        String tempID = checkActiveEditorID(page);
        if (tempID.equals(UserEditor.BID)) {
            System.out.println("You are in UserEditor.ID");
            page.closeAllEditors(true);
            EmployeeEditorInput einput = new EmployeeEditorInput();
            try {
                page.closeAllEditors(true);
                page.openEditor(einput, EmployeeEditor.ID);
                tempID = null;
            } catch (PartInitException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        } else if (tempID.equals(EmployeeEditor.BID)) {
            System.out.println("You are in EmployeeEditor.ID");
            StaffdetailsEditorInput sinput = new StaffdetailsEditorInput();
            try {
                page.closeAllEditors(true);
                page.openEditor(sinput, StaffdetailsEditor.ID);
                tempID = null;
            } catch (PartInitException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        } else if (tempID.equals(StaffdetailsEditor.BID)) {
            System.out.println("You are in StaffdetailsEditor.ID");
            FoodDetailsEditorInput finput = new FoodDetailsEditorInput();
            try {
                page.closeAllEditors(true);
                page.openEditor(finput, FoodDetailsEditor.ID);
                tempID = null;
            } catch (PartInitException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        } else if (tempID.equals(FoodDetailsEditor.BID)) {
            System.out.println("You are in FoodDetailsEditor.ID");
            EnquiryEditorInput eeinput = new EnquiryEditorInput();
            try {
                page.closeAllEditors(true);
                page.openEditor(eeinput, EnquiryEditor.ID);
                tempID = null;
            } catch (PartInitException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        } else if (tempID.equals(EnquiryEditor.BID)) {
            System.out.println("You are in EnquiryEditor.ID");
            UserEditorInput uinput = new UserEditorInput();
            try {
                page.closeAllEditors(true);
                page.openEditor(uinput, UserEditor.ID);
                tempID = null;
            } catch (PartInitException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }
    return null;
}
private String checkActiveEditorID(IWorkbenchPage page) {
    tempEditorID = page.getActiveEditor().getTitle();
    return tempEditorID;
    // TODO Auto-generated method stub
}
}
Backward Editor code:
 package handler;
 import org.eclipse.core.commands.AbstractHandler;
import org.eclipse.core.commands.ExecutionEvent;
import org.eclipse.core.commands.ExecutionException;
import org.eclipse.ui.IEditorReference;
import org.eclipse.ui.IWorkbenchPage;
import org.eclipse.ui.IWorkbenchWindow;
import org.eclipse.ui.PartInitException;
import org.eclipse.ui.handlers.HandlerUtil;
import rcp_demo.Editor.EmployeeEditor;
import rcp_demo.Editor.EmployeeEditorInput;
import rcp_demo.Editor.EnquiryEditor;
import rcp_demo.Editor.EnquiryEditorInput;
import rcp_demo.Editor.FoodDetailsEditor;
import rcp_demo.Editor.FoodDetailsEditorInput;
import rcp_demo.Editor.StaffdetailsEditor;
import rcp_demo.Editor.StaffdetailsEditorInput;
import rcp_demo.Editor.UserEditor;
import rcp_demo.Editor.UserEditorInput;
public class BackEditorHandler extends AbstractHandler {
/*
 * (non-Javadoc)
 * 
 * @see
 * org.eclipse.core.commands.IHandler#execute(org.eclipse.core.commands.
 * ExecutionEvent)
 */
String tempBackEditorID = null;
@Override
public Object execute(ExecutionEvent event) throws ExecutionException {
    System.out.println("BackEditorHandler  call");
    // TODO Auto-generated method stub
    IWorkbenchWindow window = HandlerUtil.getActiveWorkbenchWindow(event);
    IWorkbenchPage page = window.getActivePage();
    IEditorReference[] editorRefs = page.getEditorReferences();
    // get the editor instance by given id (pEditorId)
    if (page.getActiveEditor() == null || page.getActiveEditor().equals("")) {
        // Default Editor Open via command
        UserEditorInput input = new UserEditorInput();
        try {
            page.openEditor(input, UserEditor.ID);
        } catch (PartInitException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return null;
    } else {
        // First check Temp ID;
        String tempBackID = checkActiveEditorID(page);
        System.out.println("tempID:--" + tempBackID);
        if (tempBackID.equals(UserEditor.BID)) {
            System.out.println("You are in UserEditor.ID");
            page.closeAllEditors(true);
            EnquiryEditorInput eeinput = new EnquiryEditorInput();
            try {
                page.closeAllEditors(true);
                page.openEditor(eeinput, EnquiryEditor.ID);
                tempBackID = null;
            } catch (PartInitException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        } else if (tempBackID.equals(EmployeeEditor.BID)) {
            System.out.println("You are in EmployeeEditor.ID");
            UserEditorInput uinput = new UserEditorInput();
            try {
                page.closeAllEditors(true);
                page.openEditor(uinput, UserEditor.ID);
                tempBackID = null;
            } catch (PartInitException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        } else if (tempBackID.equals(StaffdetailsEditor.BID)) {
            System.out.println("You are in StaffdetailsEditor.ID");
            EmployeeEditorInput einput = new EmployeeEditorInput();
            try {
                page.closeAllEditors(true);
                page.openEditor(einput, EmployeeEditor.ID);
                tempBackID = null;
            } catch (PartInitException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        } else if (tempBackID.equals(FoodDetailsEditor.BID)) {
            System.out.println("You are in FoodDetailsEditor.ID");
            StaffdetailsEditorInput sinput = new StaffdetailsEditorInput();
            try {
                page.closeAllEditors(true);
                page.openEditor(sinput, StaffdetailsEditor.ID);
                tempBackID = null;
            } catch (PartInitException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        } else if (tempBackID.equals(EnquiryEditor.BID)) {
            System.out.println("You are in EnquiryEditor.ID");
            FoodDetailsEditorInput finput = new FoodDetailsEditorInput();
            try {
                page.closeAllEditors(true);
                page.openEditor(finput, FoodDetailsEditor.ID);
                tempBackID = null;
            } catch (PartInitException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }
    return null;
}
private String checkActiveEditorID(IWorkbenchPage page) {
    tempBackEditorID = page.getActiveEditor().getTitle();
    return tempBackEditorID;
    // TODO Auto-generated method stub
  }
  }