Java将字符串转换为双精度[重复]

Question

我正在创建一个基本的GUI，它接受用户输入的金额，并用预先存在的金额减去它。然而，它不会让我运行下面的一个，因为我得到了一个字符串不能转换为double的错误。这里使用parseInt方法不起作用，因为im使用getText方法。

String message = txtaMessage.getText();
    String transaction1 = txtfAmountTransfer.getText();
    String reciever = txtfTransferTo.getText();
    
    lblOutputTransferInfo.setText("Your Amount of "+transaction1+" has been sent to "+reciever+" .");
    lblOutputTransferMsg.setText("With a Message: "+ message);

   double balance = 5123.84;
   
   String newBalance = balance - transaction1;//this will not work but the concept I need 
   
   lblSavingsBalance.setText(newBalance);

Answer 1

如果getText返回下面的字符串，则代码将起作用。

        String message = txtaMessage.getText();
    String transaction1 = txtfAmountTransfer.getText();

    String reciever = txtfTransferTo.getText();


    lblOutputTransferInfo.setText("Your Amount of "+transaction1+" has been sent to "+reciever+" .");

    lblOutputTransferMsg.setText("With a Message: "+ message);

    double balance = 5123.84;

    balance = balance - Double.parseDouble(transaction1);//this will not work but the concept I need

    lblSavingsBalance.setText(String.valueOf(balance));

如果您使用的是android，

（假设txtaMessage、transaction1、Receiver是TextView对象或EditText对象）

txtaMessage.getText(); //This won't return a String. This will return a CharSequence.

你必须把它转换成字符串。所以正确的方法是，

String message = txtaMessage.getText().toString();

对所有编辑文本和文本视图执行此操作。

那么事务1应该转换为Double

Double.parseDouble(transaction1);

之后，可以从平衡中减去transtraction1并将其指定给原始平衡。

balance = balance - Double.parseDouble(transaction1)

android代码的完整版本如下所示。

        String message = txtaMessage.getText().toString();
    String transaction1 = txtfAmountTransfer.getText().toString();

    String reciever = txtfTransferTo.getText().toString();


    lblOutputTransferInfo.setText("Your Amount of "+transaction1+" has been sent to "+reciever+" .");

    lblOutputTransferMsg.setText("With a Message: "+ message);

    double balance = 5123.84;
    
    balance = (balance - Double.parseDouble(transaction1));//this will not work but the concept I need
        lblSavingsBalance.setText(String.valueOf(balance));

   

如果transaction1值不是数字，则会发生异常。所以用try/catch包装它是个好主意。

            try {
        balance = (balance - Double.parseDouble(transaction1));//this will not work but the concept I need
        lblSavingsBalance.setText(String.valueOf(balance));
    } catch (NumberFormatException e) {
        //Send error message like showing a toast
        e.printStackTrace();
    }

Answer 2

它不起作用，因为这里transation1是一个字符串，而balance是double。在java中，我们没有从double中减去string的方法。因此，首先，您需要将transaction1转换为double。我建议您使用双倍新天平。parseDouble（Transaction1） 然后<代码>LBL节省平衡。setText（newBalance.toString（）） 将双值转换为字符串

希望一切顺利。。。