java双到字符串错误

Question

我正在学习Java，正在做一个关于创建银行的项目，但我无法让它工作，目标是让它返回当前的银行余额和帐号，但它说不能以字符串形式返回double

public String listProjectedPortfolioTimeframe(double desiredBalance) {
    desiredBalance = 88;
    String str = "";
    double num = 200;
    String listProjectedPortfolioTimeframe = String.valueOf(listProjectedPortfolioTimeframe);
    if (bankAccounts.size() <= 0) {
        str = "enter ammount to find number of years of constant saving will give 200 euro";
        for (BankAccount ba : bankAccounts) {
            str += ba.getAccNumber();
            str += ba.getBalance();
        }
        return str;
    } else {
        return (double) (num * 100);

    }
}

Answer 1

您的else状态正在返回（双倍）（num*100）。你需要返回一个字符串

请尝试下面的代码，您需要将双精度值转换为字符串：

public String listProjectedPortfolioTimeframe(double desiredBalance) {
    desiredBalance = 88;
    String str = "";
    double num = 200;
    if (bankAccounts.size() <= 0) {
        str = "enter ammount to find number of years of constant saving will give 200 euro";
        for (BankAccount ba: bankAccounts) {
            str += ba.getAccNumber();
            str += ba.getBalance();
        }
    } else {
        str = String.valueOf(num * 100);
    }
    return str;
}

我通常不会养成为别人工作的习惯，但今天下午我有一点空闲时间：

    public String listProjectedPortfolioTimeframe(double desiredBalance) {
        String str = "";
        double amountOfIncreasePerYear = 50; // You need to replace this...
        for (BankAccount ba: bankAccounts) {
            String currentBalance = ba.getBalance();
            if(Double.parseDouble(currentBalance) <= desiredBalance)
            {
                double numberOfYears = (desiredBalance - Double.parseDouble(currentBalance)) / amountOfIncreasePerYear;
                String currentAccNumber = ba.getAccNumber();
                str += String.Format(
                    "Account#: %s, Current Balance: %.2f, Number of Years to Reach %.2f: %f \r\n",
                    currentAccNumber, currentBalance, desiredBalance, numberOfYears
                    );
            }
        }
        if(str == "") {
            str = "No Bank Accounts";
        }
        return str;
    }

我把这本记事本打印出来，好让你记住。此外，还需要确定AmountFinCreasePerYear变量中应该包含的值。什么决定了这个价值。你能从BankAccount类会员那里得到什么吗