public class TestFrame{ public static void main(String args[]){ Frame f=new Frame("Hello GUI"); f.setBackground(Color,BLUE); f.setSize(200,100); f.setVisible(true); } } 报错:--------------------Configuration: <Default>-------------------- C:\ex\09\TestFrame.java:7: cannot find symbol symbol : variable Color location: class TestFrame f.setBackground(Color,BLUE); ^ C:\ex\09\TestFrame.java:7: cannot find symbol symbol : variable BLUE location: class TestFrame f.setBackground(Color,BLUE); ^ 2 errors