java - 扫描器只允许定义的字符串

Question

我想用扫描仪通过用户输入读入运算符(operator)。只要键入预定义的运算符，扫描仪就应该读取输入。我认为它会像这样工作，但它在 while 部分返回 command cannot be resolved。

String [] operators = new String [3];
operators[0] ="!";
operators[1] ="&&";
operators[2] ="||";

Scanner sc = new Scanner(System.in);        
System.out.println("Command: ");

do {
String command = sc.next();
} while(!command.equals(operators[0]) || !command.equals(operators[1]) || !command.equals(operators[2]));

Answer 1

在 do-while 循环外声明 command 因为如果你在 do-while 循环内声明任何变量，它的范围将被限制为do-while 循环的主体。在循环体之外无法访问它。

String [] operators = new String [3];
operators[0] ="!";
operators[1] ="&&";
operators[2] ="||";
String command;

Scanner sc = new Scanner(System.in);        
System.out.println("Command: ");

do {
    command = sc.next();
} while(!command.equals(operators[0]) || !command.equals(operators[1]) || !command.equals(operators[2]));