得到一个整数的绝对值  

public static void main(String[] args) {
        demo count = new demo();
        Scanner scan = new Scanner(System.in);
        System.out.println("请输入数字");
        int x = scan.nextInt();
        System.out.println(count.abs(x));
    }
public static int abs(int x){
        return Math.abs(x);
    }