java 计算器

JFrame frame=new JFrame("计算器"); JPanel panel1=new JPanel(); JPanel panel2=new JPanel(); JButton btn0=new JButton("0"); JButton btn1=new JButton("1"); JButton btn2=new JButton("2"); JButton btn3=new JButton("3"); JButton btn4=new JButton("4"); JButton btn5=new JButton("5"); JButton btn6=new