请教java代码里的一个小问题？

//site address
    String response2=JOptionPane.showInputDialog(
        null,"Enter the site address:");
    address=new JTextField(response2,20);    //site type
    String choices[]={"Personal","Commercial","Unknow"};
    int response3=JOptionPane.showOptionDialog(
        null,"What type of site is it?","Site Type",0,
        JOptionPane.QUESTION_MESSAGE,null,choices,choices[0]);
    type=new JTextField(choices[response3],20); //??????????????请问在site type里的type=new JTextField(choices[response3],20)是什么意思
为什么他没有像site address里的address=new JTextField(response2,20)那样
choices[response3]是啥意思？choices[]不是初始化过了吗，怎么有用这个？？