写出赋值语句a:=(a-b)*b c对应的后缀式,三元式序列,四元式序列

public class SwingPro { private JFrame mainWin = new JFrame(""); private JButton ok = new JButton("确定"); private JButton cancel = new JButton("取消"); public void init() { JPanel jp = new JPanel(); // 为两个按钮设