java有一个Jbutton打印来自另一个类的内容

Question

我的addEmployee方法应该检查一次只有1名销售人员、2名设计师和4名制造人员，并检查公司的员工不超过7名，方法将返回一个字符串，指示错误是什么（即“该公司已经有一名销售人员”），或者如果添加了员工，则返回null，但我的if语句不起作用，出于某种原因，它不允许我通过说“canot return a void result”来使用消息对话框，而是强制我使用inputdialog

我的print company方法似乎有问题，但我不知道是什么，因为它只返回null，而不是打印出名称、位置和位置的arraylist

我的问题是如何解决这个问题，这样无论我在gui面板中输入什么，都会显示joptionpane中的打印，而现在我得到的joption窗格是空的

以下是代码：

public String addEmployee(String fName, String lName, String pos) {
    String message = null;

//  if (pos.equals("DESIGN")&&pos.equals("SALES")&&pos.equals("MANUFACTURING")&& numDesign==0 &&numSales==0&&numManufacturing==0)
    if (pos.equals("DESIGN")&&pos.equals("SALES")&&pos.equals("MANUFACTURING")&& numDesign==0 &&numSales==0&&numManufacturing==0)
    {
         return JOptionPane.showInputDialog(null,"woow ",JOptionPane.ERROR_MESSAGE);
    }
    if (pos.equals("DESIGN")&& numDesign==1&&numSales!=2&&numManufacturing!=4)
    {
        p2=Position.DESIGN;
        addEmp = new Employees(fName, lName, pos);
        list.add(addEmp);
        numDesign++;
//  message="There are already"+ (numDesign++) +" design persons\nEmployee not added";

    }//else  return message;

    else if (pos.equals("SALES")&&numDesign<1&&numSales<2&&numManufacturing<4)
    {
        //String error;
        p2=Position.SALES;
        addEmp = new Employees(fName, lName,pos);
        list.add(addEmp);
        numSales++;

    }//else return JOptionPane.showInputDialog(null," There is already a sales person\nEmployee not added");
    else if (pos.equals("MANUFACTURING")&& numDesign<1&&numSales<2&&numManufacturing<4)
    {
        p2=Position.MANUFACTURING;
        addEmp = new Employees(fName, lName, pos);
        list.add(addEmp);
        numManufacturing++;
        //p2.MANUFACTURING++;
    }//else return JOptionPane.showInputDialog(null," There are already four manufacturing persons \nEmployee not added ","Empolyees", JOptionPane.ERROR_MESSAGE);

     if (numSales<1)
     {
         return JOptionPane.showInputDialog(null," There is already a sales person\nEmployee not added");
     }
     if (numDesign<2)
     {
         return JOptionPane.showInputDialog(null, "There are already"+ (numDesign++) +" design persons\nEmployee not added");
     }
    if (numberOfCompanies<3)
    {
        return JOptionPane.showInputDialog(null,"There are already two companies Company not added","Empolyees", JOptionPane.ERROR_MESSAGE);
    }
    if (numManufacturing<4)
    {
         return JOptionPane.showInputDialog(null," There are already four manufacturing persons \nEmployee not added ","Empolyees", JOptionPane.ERROR_MESSAGE);
    }
    if (numEmployees<7)
    {
        return  JOptionPane.showInputDialog(null,"There are already 7 employees\nEmployee not added","Empolyees", JOptionPane.ERROR_MESSAGE);//check.toString();//look
         // System.out.println(check.printCompany());
    }

    return null;
    // TODO Auto-generated method stub

}

/*public Company(String str) {
    // TODO Auto-generated constructor stub
    //
}*/





public String printCompany( ) {
    // TODO Auto-generated method stub
    String str = null;
    for (int index=0; index<list.size();index++)
    {
        str+=list.get(index).getFName()+" "+list.get(index).getLName()+" "+"Position:"+list.get(index).getPosition();
        System.out.println(str);
    }
    return str;

}
public String toString()
{
    int index=0;

    String str =list.get(index).getFName()+" "+list.get(index).getLName()+" "+"Position:"+list.get(index).getPosition();
    System.out.println(str);;
    return JOptionPane.showInputDialog(null,str);
}

这是我试图从printcompany方法打印arraylist的gui类：

private class ButtonListener implements ActionListener

{

    @Override
    public void actionPerformed(ActionEvent e) {    
        // TODO Auto-generated method stub


        String lnameInput;


        String fNameInput;
        lnameInput= lNameText.getText();


        fNameInput=fNameText.getText();


        if(e.getSource() == addEmpButton){

        if(design.isSelected())
        {
            check.addEmployee(fNameInput, lnameInput, "Design");

        }

        if(sales.isSelected())
        {
            check.addEmployee(fNameInput, lnameInput, "Sales");
        }

        if(manufacturing.isSelected())
        {
            check.addEmployee(fNameInput, lnameInput, "Manufacturing");
        }

        }

        if(e.getSource() == clearButton)
                {
            lNameText.setText("");
            fNameText.setText("");
                }
         if (e.getSource() == printEmpsButton) {
                     JOptionPane.showMessageDialog(null,check.printCompany());//look
                  System.out.println(check.printCompany());
              }

        if (e.getSource() == exitButton) {
            System.exit(0);
            }

        if(e.getSource() == newCompButton)
                {
        //  check = null;
            check = new Company(companyN);
            message=JOptionPane.showInputDialog(null, "What is the name of this Company?","Company Name", JOptionPane.PLAIN_MESSAGE);
                }







    }


}