如何检查变量是否为空？

Question

我知道这不起作用，但我怎么知道用户是否添加了一个字符？

public class Program
import java.util.Scanner;
{
public static void main(String[] args) {
    Scanner a = new Scanner(System.in);
    String b = a.nextLine();

//I know this doesnt work but how can I know if the user added even one char?
    if (b!=null){
    System.out.println(b);
}
}
}

Answer 1

您可以使用.equals("")或.isEmpty()

检查check if the variable is null

Answer 2

你可以这样做

if (!b.isEmpty()) {
  System.out.println(b);
}