为什么这个程序上按钮的文本看不见啊？？请大家帮我看看怎么回事！！
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
 
class Counter extends JFrame
{  
      //实例化2个显示屏
      JTextField Jtextfield1=new JTextField(20);
      JTextField Jtextfield2=new JTextField(5);
      
      //实例化4个面板
      JPanel Jpanel1=new JPanel();
      JPanel Jpanel2=new JPanel();
      JPanel Jpanel3=new JPanel();
      JPanel Jpanel4=new JPanel();
      
      //实例化布局管理器
      GridLayout GLayout3=new GridLayout(1,3);
      GridLayout GLayout4=new GridLayout(4,5);
      
      //实例化按钮
       JButton[][] b=new JButton[][]{{new JButton("MC"),
                                      new JButton("MR"),
                                      new JButton("MS"),
                                      new JButton("M+")},
                            
                                     {new JButton("Backspace"),
                                      new JButton("CE"),
                                      new JButton("C")},
                            
                                     {new JButton("0"),
                                      new JButton("1"),
                                      new JButton("2"),
                                      new JButton("3"),
                                      new JButton("4"),
                                      new JButton("5"),
                                      new JButton("6"),
                                      new JButton("7"),
                                      new JButton("8"),
                                      new JButton("9"),
                                      new JButton("/"),
                                      new JButton("*"),
                                      new JButton("-"),
                                      new JButton("+"),
                                      new JButton("sqrt"),
                                      new JButton("%"),
                                      new JButton("1/x"),
                                      new JButton("="),
                                      new JButton("+/-")}
                                    };
                           
      ActionListener action=new ActionListener()
      {
            public void actionPerformed(ActionEvent e)
            {
                    Jtextfield1.setText(" ");
            }
      }; 
      
      public Counter(String str)
      {
              super(str);
              setLayout(null);
        setJPanel1();
        setJPanel2();
        add(Jpanel1);
        add(Jpanel2);
        for(int i=0;i<b.length;i++)
        { 
          for(int j=0;j<b[i].length;j++)
          {
                  b[i][j].addActionListener(action);
          }
        } 
      }
      public void setJPanel1()
      {
              GridLayout GLayout1=new GridLayout(1,1);
              Jpanel1.setLayout(GLayout1);
              Jpanel1.add(Jtextfield1);
              Jtextfield1.setHorizontalAlignment(JTextField.RIGHT );
              Jpanel1.setBounds(10,3,252,22);
      }
      public void setJPanel2()
      {
              GridLayout GLayout2=new GridLayout(5,1,10,10);
              Jpanel2.setLayout(GLayout2);
              Jpanel2.add(b[0][0]);
              Jpanel2.add(b[0][1]);
              Jpanel2.add(b[0][2]);
              Jpanel2.add(b[0][3]);
              Jpanel2.setBounds(10,40,40,180);
      }
        public static void main(String[] args)
        {
                Counter counter=new Counter("计算器");
                counter.setSize(280,250);
                counter.setLocation(300,250);
                counter.setVisible(true);
                counter.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        }
}