java - 为什么当我调用另一个类的构造函数时会出现空指针异常？

Question

case "Login":
        try {
            restoreUserInfo();
            String email = textf1.getText();
            String password = new String(jpass1.getPassword());
            if (hm.containsKey(email)) {
                if (hm.get(email).getPassword().equals(password)) {
                    showMessageDialog(this, "Successfully login");

                    ch = new Chat_Window("lets chat!!");
                    System.out.println("after call");

                } else {
                    showMessageDialog(this, "Invalid Password");
                }
            } else {
                showMessageDialog(this, "Invalid Login ID and Password");
            }
        } catch (Exception exc) {
            System.out.println("Invalid file");
            exc.printStackTrace();
        }

为什么当我调用“ch = new Chat_Window("lets chat!!");”时会出现空指针异常？Chat_window 类在同一个包中可用，并且具有匹配的构造函数，代码如下：

public Chat_Window(String title){
    super(title);
    setSize(500, 500);
    getContentPane().setBackground(Color.LIGHT_GRAY);
    setLocationRelativeTo(null);
    setResizable(false);
    c1=new JPanel();
    c2=new JPanel();
            lbl=new JLabel("Type Here:");
    c1.add(lbl, new GridLayout(1, 2, 50, 50));
    ta=new JTextArea(03,30);
    c1.add(ta,new GridLayout(1, 2, 50, 50) );
    c1.add(send_but,new GridLayout(1, 2, 50, 50));
    add(c1, BorderLayout.PAGE_END);
    send_but=new JButton("Send");
            setDefaultCloseOperation(EXIT_ON_CLOSE);
    setVisible(true);

}

请帮忙！！！

Answer 1

send_but在创建之前添加。

c1.add(send_but,new GridLayout(1, 2, 50, 50));  // send_but is null here
add(c1, BorderLayout.PAGE_END);
send_but=new JButton("Send");