计算成绩算法

package j;

import java.awt.Frame;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

import javax.swing.Icon;
import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JTextField;

public class j {

public static void main(String[] args) 
{

Frame f=new Frame();
f.setLayout(null);//自由布局
f.setTitle("成绩判定");//设置标题
f.setSize(586, 540);//调整大小
f.setLocation(100, 100);//设置窗口位置
JLabel l1=new JLabel("成绩");
l1.setBounds(200, 150, 50, 50);
f.add(l1);
JTextField t=new JTextField("请输入成绩");
t.setBounds(300, 160, 100, 30);
f.add(t);
JButton b1=new JButton("确定");
JButton b2=new JButton("取消");
b1.setBounds(200,230,80,30);
f.add(b1);
b2.setBounds(320,230,80,30);
f.add(b2);
t.addMouseListener(new MouseAdapter() {
public void mouseClicked(MouseEvent e) {
t.setText("");}
});
b1.addMouseListener(new MouseAdapter() {
public void mouseClicked(MouseEvent e) 
{
String s;
s=t.getText();
try 
{
int a = 0;
a= Integer.parseInt(s);
if(a<60&&a>=0)
{
JOptionPane.showMessageDialog(null, "不及格");
}
else if(a<70&&a>=0)
{
JOptionPane.showMessageDialog(null, "及格");
}
else if(a<80&&a>=0)
{
JOptionPane.showMessageDialog(null, "中");
}
else if(a<90&&a>=0)
{
JOptionPane.showMessageDialog(null, "良");
}
else if(a<=100&&a>=0)
{
JOptionPane.showMessageDialog(null, "优");
}
else 
{
JOptionPane.showMessageDialog(null, "输入错误");
}
}
catch (NumberFormatException e1) 
{

JOptionPane.showMessageDialog(null, "输入错误");
}

}
});
b2.addMouseListener(new MouseAdapter() {
public void mouseClicked(MouseEvent e) 
{

System.exit(0);
}
});
f.addWindowListener
(
new WindowAdapter() {
public void windowClosing(WindowEvent e) {
System.exit(0);
}
}
);
Icon i1 = new ImageIcon("2.jpg");

JLabel bg=new JLabel(i1);
bg.setBounds(0,0, 586,540);
f.add(bg);
f.setVisible(true);//显示窗口

}
}