What's the best way to check if a String represents an integer in Java?

If you are not concerned with potential overflow problems this function will perform about 20-30 times faster than using Integer.parseInt().

public static boolean isInteger(String str) {    if (str == null) {        return false;    }    int length = str.length();    if (length == 0) {        return false;    }    int i = 0;    if (str.charAt(0) == '-') {        if (length == 1) {            return false;        }        i = 1;    }    for (; i < length; i++) {        char c = str.charAt(i);        if (c < '0' || c > '9') {            return false;        }    }    return true;}

You have it, but you should only catch NumberFormatException.

Did a quick benchmark. Exceptions aren't actually that expensivve, unless you start popping back multiple methods and the JVM has to do a lot of work to get the execution stack in place. When staying in the same method, they aren't bad performers.

 public void RunTests() {     String str = "1234567890";     long startTime = System.currentTimeMillis();     for(int i = 0; i < 100000; i++)         IsInt_ByException(str);     long endTime = System.currentTimeMillis();     System.out.print("ByException: ");     System.out.println(endTime - startTime);     startTime = System.currentTimeMillis();     for(int i = 0; i < 100000; i++)         IsInt_ByRegex(str);     endTime = System.currentTimeMillis();     System.out.print("ByRegex: ");     System.out.println(endTime - startTime);     startTime = System.currentTimeMillis();     for(int i = 0; i < 100000; i++)         IsInt_ByJonas(str);     endTime = System.currentTimeMillis();     System.out.print("ByJonas: ");     System.out.println(endTime - startTime); } private boolean IsInt_ByException(String str) {     try     {         Integer.parseInt(str);         return true;     }     catch(NumberFormatException nfe)     {         return false;     } } private boolean IsInt_ByRegex(String str) {     return str.matches("^-?\\d+$"); } public boolean IsInt_ByJonas(String str) {     if (str == null) {             return false;     }     int length = str.length();     if (length == 0) {             return false;     }     int i = 0;     if (str.charAt(0) == '-') {             if (length == 1) {                     return false;             }             i = 1;     }     for (; i < length; i++) {             char c = str.charAt(i);             if (c <= '/' || c >= ':') {                     return false;             }     }     return true; }

Output:

ByException: 31

ByRegex: 453 (note: re-compiling the pattern every time)

ByJonas: 16

I do agree that Jonas K's solution is the most robust too. Looks like he wins :)