Java Can not Cast from String to Integer_Sovled

Question

HashMap<String, String> config = Feeds.config; 

String num =  config.get("NumOfFeeds");

System.out.println(num);

feedsAmount = ((Integer)num).intValue();

System.out.println(feedsAmount);

I've also tried Integer.parseInt(num) and Integer.decode(num) and Integer.valueof(bu)

Results as follows: 40

Exception in thread "main" java.lang.NumberFormatException: For input string:"40"
at java.lang.NumberFormatException.forInputString(NumberFormatException.java:48)
at java.lang.Integer.parseInt(Integer.java:458)
at java.lang.Integer.parseInt(Integer.java:499)
at fetch_RSS.<init>(fetch_RSS.java:40)
at testing.main(testing.java:27)

The problem was caused by different encoding from the txt file I'm reading from and the encoding in Elipse which is the macRoman by default.

Answer 1

The correct way of working is this:

String num = config.get("NumOfFeeds");
int feeds = Integer.parseInt(num);

This, only when you are sure that the String is representing a number the valid way.

-30         // correct
0           // correct
2000        // correct


"40"        // invalid
40          // valid

2.000       // invalid
2.000.000   // invalid
20,0        // invalid
2,000,000   // invalid

Answer 2

Your exception got raised in Integer.java:458.

Looking into the source code of Integer I see that some characters of your String "40" returned a negative value (most probably -1) for Character.digit(s.charAt(i++), radix) where i is iterating over String's characters and radix is 10.

This should not happen normally. But it happens when the String is "4o" and not "40" like @Løkling's wild guess in the comments.

You should debug here to see what really happens.

Answer 3

Of course you can't cast from String to Integer. A String is not a Integer, and Integer is not a String.

You have to use int i = Integer.parseInt(..). It works if the string is a properly formatted integer.

Answer 4

For a cast to succeed in Java, the reference being cast must point to an object that is actually an instance of the type being cast to. A reference to String can't be cast to Integer because an object couldn't possibly be both things.

(This is somewhat unlike a cast in C, which is basically just saying, reinterpret the data stored here according to a different datatype. It would still be incorrect in C to use casting as a method to convert a string representing a number to a numeric value.)

Integer.parseInt is what you are looking for here. What problem are you having with it?

Answer 5

Remember : In java, we can only cast between objects if they are EXPLICITLY of the same type ! In other languages , like python, we can do the casting you requested here, because those languages allow "duck typing".

You must use Integer.parseInt("1234"), to create an Integer object from a String.

Alternatively you could create an Object wrapper to your data :

class MyObject
{
    Object input; 
   public MyObject(Object input)
    {
         this.input=input;
    }

    public Integer getInt()
   {  
    return Integer.parseInt(input.toString());
   }
    public String getString()
   {
       return input.toString();
   }
} 

This would be overkill for your simple problem, however :)