Java Swing 调用了自定义对话框，对话框里面的内容为什么显示不了？？

我写了一个自定义对话框的类来接收参数，调试的时候对话框没有任何问题，但放到主程序调用的时候，对话框里面的所有控件都显示不了， setVisible(true); 这个语句放到哪里都没用。

在网上查了很多资料，还是没有解决，望望各位大神指条明路，谢谢

代码如下：

public class ParaRequestDialog extends JDialog {
    private Map<String, String> para;
    private boolean isReceived = false;

    private Map<String, JTextField> paraTexts = new HashMap<>();

    public ParaRequestDialog(Map<String, String> para) {
        this.para = para;
        int num = para.size() - 1;
        int height = num * 35 + 80;

        setLayout(null);
        setDefaultCloseOperation(DISPOSE_ON_CLOSE);
        setTitle("请输入以下参数值：");
        setBounds( 200,300,290, height);

        int i = -1;
        for (String key : para.keySet()) {
            if (key.equals("isReceived"))
                continue;
            i++;
            JLabel label = new JLabel(key + ":");
            label.setBounds(20, i * 35 + 10, 50, 25);
            JTextField text = new JTextField();
            text.setBounds(75, i * 35 + 10, 180, 25);
            paraTexts.put(key, text);

            add(label);
            add(text);
        }

        JButton confirm = new JButton("确定");
        confirm.addActionListener(this::ConfirmAction);
        JButton cancel = new JButton("取消");
        cancel.addActionListener(this::CancelAction);

        confirm.setBounds(60, height - 70, 60, 25);
        cancel.setBounds(150, height - 70, 60, 25);
        add(confirm);
        add(cancel);
        setVisible(true);
    }

    private void ConfirmAction(ActionEvent actionEvent) {
        for (String key : paraTexts.keySet()) {
            para.put(key, paraTexts.get(key).getText());
        }
        para.put("isReceived", "true");
        isReceived = true;
        this.dispose();
    }

    private void CancelAction(ActionEvent actionEvent) {
        para.put("isReceived", "false");
        isReceived = false;
        this.dispose();
    }

    public Map<String, String> getPara() { return para; }

    public boolean isReceived() { return isReceived; }
}

自定义框代码呢?

缺少main

import java.awt.event.ActionEvent;
import java.util.HashMap;
import java.util.Map;

import javax.swing.*;
import javax.swing.JTable;
import javax.swing.table.DefaultTableModel;

public class ParaRequestDialog extends JDialog {
    private Map<String, String> para;
    private boolean isReceived = false;
 
    private Map<String, JTextField> paraTexts = new HashMap<>();
 
    public ParaRequestDialog(Map<String, String> para) {
        this.para = para;
        int num = para.size() - 1;
        int height = num * 35 + 80;
 
        setLayout(null);
        setDefaultCloseOperation(DISPOSE_ON_CLOSE);
        setTitle("请输入以下参数值：");
        setBounds( 200,300,290, height);
 
        int i = -1;
        for (String key : para.keySet()) {
            if (key.equals("isReceived"))
                continue;
            i++;
            JLabel label = new JLabel(key + ":");
            label.setBounds(20, i * 35 + 10, 50, 25);
            JTextField text = new JTextField();
            text.setBounds(75, i * 35 + 10, 180, 25);
            paraTexts.put(key, text);
 
            add(label);
            add(text);
        }
 
        JButton confirm = new JButton("确定");
        confirm.addActionListener(this::ConfirmAction);
        JButton cancel = new JButton("取消");
        cancel.addActionListener(this::CancelAction);
 
        confirm.setBounds(60, height - 70, 60, 25);
        cancel.setBounds(150, height - 70, 60, 25);
        add(confirm);
        add(cancel);
        setVisible(true);
    }
 
	private void ConfirmAction(ActionEvent actionEvent) {
        for (String key : paraTexts.keySet()) {
            para.put(key, paraTexts.get(key).getText());
        }
        para.put("isReceived", "true");
        isReceived = true;
        this.dispose();
    }
 
    private void CancelAction(ActionEvent actionEvent) {
        para.put("isReceived", "false");
        isReceived = false;
        this.dispose();
    }
 
    public Map<String, String> getPara() { return para; }
 
    public boolean isReceived() { return isReceived; }
    
    public static void main(String[] argv) throws Exception {

        
		HashMap hm = new HashMap<>();
        hm.put("Username", "Username");
        hm.put("Password", "Password");
        
        ParaRequestDialog f = new ParaRequestDialog(hm);
        f.setSize(550, 350);

        f.setVisible(true);
     }
}