JOptionPane 中的 NullpointerException

Question

****它在 JOptionPane 代码中抛出 NullPointerException，如下所示。****

public static void main(String[]args){


    String[] options={"Do it again?", "Exit"};
    int response=0;
    int indexOfZip;
    do{
        try{

        String dataStr=JOptionPane.showInputDialog("Enter a zip code");


        if(dataStr!=null){
             while (k<i){
                 if (place[k].equals(dataStr)){

                 indexOfZip=k;
                     k++;
                 }

             }
             int data=Integer.parseInt(dataStr);
             response=JOptionPane.showOptionDialog(null,
                           "You asked me to search for zip code:"+dataStr+"The zip code "+dataStr+" belongs to"+place[k].getTown()+","+place[k].getState()+"Do you want me to search again?",
                           "results",

                           JOptionPane.YES_NO_OPTION,
                           JOptionPane.QUESTION_MESSAGE,
                           null,
                           options,options[0]);


             System.out.println("You asked me to search for zip code:"+dataStr);
             System.out.println("The zip code "+dataStr+" belongs to"+place[k].getTown()+","+place[k].getState());
             System.out.println("Do you want me to search again?");

        }


        }catch(NumberFormatException e){
        JOptionPane.showMessageDialog(null,"Bad Numeric String, try again.", "Input Error",JOptionPane.ERROR_MESSAGE);

         }
    }while(response==0);
    if (response!=0){
       System.out.print("No");
       System.out.println("Good Bye!");
    }



    }

终端说异常是针对这一行响应=JOptionPane.showOptionDialog（空，

但是我看不出这里有什么问题，因为"response"之前已经初始化了。

Answer 1

看来place[k]一定是null, place[k].getTown() 触发 NullPointerException。在调试器中观察 place[k] 的值（或添加打印语句）。

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