java字符串值应该在double.valueof（..）中使用

Question

I am creating .jsp page and reiceve error about it ;

        String energyv="";

        int number= Integer.parseInt(request.getParameter("number"));
        energyv="_"+number;
    *
    *
    *
        if (tokenNumber == 2 && found && value1.equals("")) {
        value1= nextToken;
        if (value1.equals(""))
        found = false;

        }

        if (tokenNumber == 3 && found && value2.equals("")) {
        value2= nextToken;

        }

*
*
*
        Double activeTotalLong = Double.valueOf( "value" + energyv );

*
*
*

When try to do this I recieve tomcat error;

02 Aug 2012 11:17:30,097 ERROR http-8080-4 org.apache.catalina.core.ContainerBase.[Catalina].[localhost].[/PlantVisorPRO].[jsp] - Servlet.service() for servlet jsp threw exception java.lang.NumberFormatException: For input string: "value2" at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1224) at java.lang.Double.valueOf(Double.java:475)

Java can create my value ( like a value2 or value1), but how can i fix string problem ?

Answer 1

Double activeTotalLong = Double.valueOf( "value" + energyv );

This method takes valid numbers represented in a string.

"value2" isn't a valid number format.

Example usages of Double.valueOf():

Double d;
d = Double.valueOf("23.72");
d = Double.valueOf("-1.247002");
d = Double.valueOf("1e9"); // e  =    *10^()

---

So, what you are trying to do is, get the value of value2 or value1 . And what you actually wrote is

   "value" + 2
=  "value2"    // This is a string! not a variable!

So, to solve this, there are two options:

• use arrays
• use if-else

---

Using arrays:

String values[] = new String[2];
values[0] = value1;
values[1] = value2;
Double.valueOf(values[energyv - 1]);

Using if-else:

Double activeTotalLong;
if (energyv == 1)
{
    activeTotalLong = Double.valueOf(value1);
} else if (energyv == 2)
{
    activeTotalLong = Double.valueOf(value2);
}