直到调整窗口大小，GUI元素才会显示

您永远不会将内容添加到Jframe。您需要进行的最少更改：

  public static void main(String args[]){    final main main = new main();    SwingUtilities.invokeLater(new Runnable(){      public void run(){        initComponents(main);      }    });  }

然后修改

initComponents

main

  public static void initComponents(main main){    Jframe loginframe = new Jframe("Encrypted Chat - Login");    loginframe.setDefaultCloseOperation(Jframe.EXIT_ON_CLOSE);    main loginPanel = new main();    loginPanel.setLayout(new FlowLayout());    loginframe.setSize(300, 125);    loginframe.setResizable(false);    loginframe.setVisible(true);    loginframe.add(main);  // <----- this line is added  }