为什么这个JOptionPane命令不起作用？

Question

为什么这个JOptionPane命令不起作用？

  if (let != 'D' || let != 'S' || let != 'M' || let != 'A' || let != 'X'){
  JOptionPane.showMessageDialog (null, "Wrong character entered.", 
  JOptionPane.ERROR_MESSAGE);}

它似乎给了我错误信息：

JOptionPane.showMessageDialog (null, "Wrong character entered.", JOptionPane.ERROR_MESSAGE);}
             ^
method JOptionPane.showMessageDialog(Component,Object,String,int,Icon) is not applicable (actual and formal argument lists differ in length)
method JOptionPane.showMessageDialog(Component,Object,String,int) is not applicable (actual and formal argument lists differ in length)
method JOptionPane.showMessageDialog(Component,Object) is not applicable (actual and formal argument lists differ in length)

Answer 1

您忘记了title参数。它应该在消息后立即传递：

JOptionPane.showMessageDialog (null, 
                               "Wrong character entered.", 
                               "Title", 
                               JOptionPane.ERROR_MESSAGE);

有关此方法的详情，请访问here。

Answer 2

您试图通过传递错误的参数来调用方法。没有像JOptionPane.showMessageDialog(Component parentComponent,String message,int messageType）这样的方法。

可能你正在寻找这种方法。 JOptionPane#showMessageDialog(Component parentComponent, Object message, String title, int messageType)。 您可以将String作为DialogBox的标题传递。

所以改变

JOptionPane.showMessageDialog (null, "Wrong character entered.", JOptionPane.ERROR_MESSAGE);

到

JOptionPane.showMessageDialog (null, "Wrong character entered.", "Attention!" ,JOptionPane.ERROR_MESSAGE);