Scanner scanner = new Scanner(System.in);

System.out.print("上次成绩：");

int prev = scanner.nextInt();

System.out.print("本次成绩：");

int score = scanner.nextInt();

double percent = (double)(score - prev) / prev * 100;

if (percent < 0) {

    System.out.printf("成绩退步了%.2f%%", Math.abs(percent));

} else {

    System.out.printf("成绩提高了%.2f%%", percent);

}