Question

我是java新手，我必须使用写withdraw方法检查帐户中是否有足够的内容。
如果帐户余额低于0，则会打印出一条消息Insufficient funds。

我尝试了以下内容：

public double withdraw(double accountbalance) {
    if(accountbalance <= 0) {
        return "Insufficient funds";
    }
}

Answer 1

根据方法名称withdraw(...)，我认为应该在此处进行减法，应该有accountbalance和withdrawAmount，值不足应该是accountbalance<withdrawAmount

您需要修改从double到String

的返回类型

public String withdraw(double accountbalance)
 {
     if(accountbalance <=0){
         return "Insufficient funds";
     }
     return "Suffcient";
 }

或者，我建议退回double，如果没有足够的价值，只需返回0.否则返回您要求的金额

Answer 2

将您的返回类型更改为String而不是Double

public String withDraw(double accountbalance) {
    if(accountbalance<=0) {
        return "Insfufficient funds";
    }
    return "Money is there";
}

Answer 3

你需要返回一个String no double 并且必须在if之外。例如：

public String withdraw(double accountbalance)
   String str="";

   if (accountbalance <= 0)
   {
     str="Insufficient funds"; 
   }
   return str;
 }

Answer 4

我认为，负帐户余额是一个例外，因此应该如此实施。

public double withdraw(double amount) {
  if (accountBalance - amount < 0) {
    // throwing an exception ends the method
    // similar to a return statement
    throw new IllegalStateException("Insufficient funds");
  }
  // this is only executed,
  // if the above exception was not triggered
  this.accountBalance -= amount;
}

现在你可以这样称呼：

public String balance(double amount) {
  // to handle potentially failing scenarios use try-catch
  try {
    double newBalance = this.account.withDraw(amount)
    // return will only be executed,
    // if the above call does not yield an exception
    return String.format(
      "Successfully withdrawn %.2f, current balance %.2f", 
      amount,  
      newBalance
    );
  // to handle exceptions, you need to catch them
  // exceptions, you don't catch will be raised further up
  } catch (IllegalStateException e) {
    return String.format(
      "Cannot withdraw %.2f: %s", 
      e.getMessage()
    );
  }
}

String.format是一个方便的实用程序，用于格式化Strings而不会混淆它们。它使用占位符，它们在各自的顺序中以格式String之后的变量替换。

%s代表String。

%f是占位符，用于浮点数。在上面的例子中，我使用%.2f将浮点数格式化为小数点后的2位数。

有关异常处理的更多信息，请参阅official documentation或one of the many tutorials中有关该主题的内容。

如何在java中为double方法返回一个字符串

4 个答案: