Scanner sc = new Scanner(System.in);
System.out.print("请输入一个数:");
double number = sc.nextDouble();
if(number==0)System.out.println("这是0");
else if(number>0)System.out.println("正数");
else System.out.println("负数");
zhezhongwentishuozhengde,nihaishibuyaixuele.