parseInt is the way to go. The Integer documentation says
Use parseInt(String) to convert a string to a int primitive, or use valueOf(String) to convert a string to an Integer object.
parseInt is likely to cover a lot of edge cases that you haven't considered with your own code. It has been well tested in production by a lot of users.
Integer.parseInt is best way to convert String to Int in Java? - Stack Overflow
java - Good way to encapsulate Integer.parseInt() - Stack Overflow
[Java]Why will Integer.parseInt() not work for my String?
what is meant by parseint?
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parseInt is the way to go. The Integer documentation says
Use parseInt(String) to convert a string to a int primitive, or use valueOf(String) to convert a string to an Integer object.
parseInt is likely to cover a lot of edge cases that you haven't considered with your own code. It has been well tested in production by a lot of users.
I invite you to look at the source code of the parseInt function. Your naïve function is faster, but it also does way less. Edge cases, such as the number being to large to fit into an int or not even being a number at all, will produce undetectable bogus results with your simple function.
It is better to just trust that the language designers have done their job and have produced a reasonably fast implementation of parsing integers. Real optimization is probably elsewhere.
You could return an Integer instead of an int, returning null on parse failure.
It's a shame Java doesn't provide a way of doing this without there being an exception thrown internally though - you can hide the exception (by catching it and returning null), but it could still be a performance issue if you're parsing hundreds of thousands of bits of user-provided data.
EDIT: Code for such a method:
public static Integer tryParse(String text) {
try {
return Integer.parseInt(text);
} catch (NumberFormatException e) {
return null;
}
}
Note that I'm not sure off the top of my head what this will do if text is null. You should consider that - if it represents a bug (i.e. your code may well pass an invalid value, but should never pass null) then throwing an exception is appropriate; if it doesn't represent a bug then you should probably just return null as you would for any other invalid value.
Originally this answer used the new Integer(String) constructor; it now uses Integer.parseInt and a boxing operation; in this way small values will end up being boxed to cached Integer objects, making it more efficient in those situations.
What behaviour do you expect when it's not a number?
If, for example, you often have a default value to use when the input is not a number, then a method such as this could be useful:
public static int parseWithDefault(String number, int defaultVal) {
try {
return Integer.parseInt(number);
} catch (NumberFormatException e) {
return defaultVal;
}
}
Similar methods can be written for different default behaviour when the input can't be parsed.
This code is to simulate a simple evaluation of a postfix string. But I'm having trouble converting my variable String token to an int value.
I get the compliation error: "Error: The method parseInt(java.lang.String) is undefined for the type Integer" http://ideone.com/fzWFvp
Edit: heres the main file for testing http://ideone.com/5YwSno