给定一个百分制的分数，输出相应的等级。         

90分以上        A级         

80~89          B级         

70~79          C级        

60~69          D级         

60分以下        E级 

解决方法：

import java.util.*;class Mark{    public static void main(String []args){        System.out.println("please input marks:");        double mark;        Scanner scanner = new Scanner(System.in);        mark = scanner.nextDouble();    if(mark<0||mark>100){        System.out.println("输入有误！");        System.exit(0);        }    if(mark>=90)        System.out.println("this mark is grade \'A\'");    else if(mark>=80)        System.out.println("this mark is grade \'B\'");    else if(mark>=70)        System.out.println("this mark is grade \'C\'");    else if(mark>=60)        System.out.println("this mark is grade \'D\'");    else        System.out.println("this mark is grade \'E\'");    }}