Best implementation for an isNumber(string) method

Question

In my limited experience, I've been on several projects that have had some sort of string utility class with methods to determine if a given string is a number. The idea has always been the same, however, the implementation has been different. Some surround a parse attempt with try/catch ``` public boolean isInteger(String str) { try { Integer.parseInt(str); return true; } catch (NumberFormatException nfe) {} return false; } ``` and others match with regex ``` public boolean isInteger(String str) { return str.matches("^-?[0-9]+(\.[0-9]+)?$"); } ``` Is one of these methods better than the other? I personally prefer using the regex approach, as it's concise, but will it perform on par if called while iterating over, say, a list of a several hundred thousand strings? Note: As I'm kinda new to the site I don't fully understand this Community Wiki business, so if this belongs there let me know, and I'll gladly move it. EDIT: With all the TryParse suggestions I ported Asaph's benchmark cod…

Accepted Answer

I just ran some benchmarks on the performance of these 2 methods (On Macbook Pro OSX Leopard Java 6). ParseInt is faster. Here is the output:

```
This operation took 1562 ms.
This operation took 2251 ms.
```

And here is my benchmark code:

```
public class IsIntegerPerformanceTest {

public static boolean isIntegerParseInt(String str) {
        try {
            Integer.parseInt(str);
            return true;
        } catch (NumberFormatException nfe) {}
        return false;
    }

public static boolean isIntegerRegex(String str) {
        return str.matches("^[0-9]+$");
    }

public static void main(String[] args) {
        long starttime, endtime;
        int iterations = 1000000;
        starttime = System.currentTimeMillis();
        for (int i=0; i<iterations; i++) {
            isIntegerParseInt("123");
            isIntegerParseInt("not an int");
            isIntegerParseInt("-321");
        }
        endtime = System.currentTimeMillis();
        System.out.println("This operation took " + (endtime - starttime) + " ms.");
        starttime = System.currentTimeMillis();
        for (int i=0; i<iterations; i++) {
            isIntegerRegex("123");
            isIntegerRegex("not an int");
            isIntegerRegex("-321");
        }
        endtime = System.currentTimeMillis();
        System.out.println("This operation took " + (endtime - starttime) + " ms.");
    }
}
```

Also, note that your regex will reject negative numbers and the parseInt method will accept them.

Best implementation for an isNumber(string) method

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