您的条件是否正常，除了您不想两次调用scanner.next()，这会吃掉"一些输入.

Your if condition is OK, except that you don't want to call scanner.next() twice, which will 'eat' some input.

您希望将scanner.next()的值设置为变量，然后在if条件下检查变量值:

You would want to set the value of scanner.next() to a variable and then check the variable value in the if condition:

String input = scanner.next(); 
if(input == null || input.equals("")){
    //Do something
}