如何在java中为double方法返回一个字符串

Question

我是 Java 新手，我必须编写一个 withdraw 方法来检查帐户中是否有足够的资金。
如果账户余额低于0，它只会打印出一条消息说Insufficient funds。

我尝试了以下方法：

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

Answer 1

你需要返回一个没有双精度的字符串 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 2

根据方法名withdraw(...)，我相信这里应该有减法，应该有accountbalance和withdrawAmount，值不足应该是accountbalance<withdrawAmount

您需要将返回类型从double 修改为String

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

或者，我建议返回double，如果没有足够的值，则返回0。否则返回您要求的金额

Answer 3

我认为，负账户余额是一个例外，因此应该这样实施。

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它：

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      "Successfully withdrawn %.2f, current balance %.2f", 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，而无需将它们连接起来。它使用占位符，这些占位符被格式String之后的变量替换为相应的顺序。

%s 代表String。

%f 是一个占位符，用于浮点数。在上述情况下，我使用了%.2f，它将浮点数格式化为小数点后2位。

有关异常处理的更多信息可以在official documentation 或one of the many tutorials 中找到关于该主题的信息。

Answer 4

将返回类型更改为 String 而不是 Double

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