Regex or Exception Handling?

Question

Which one of the following is a better practice to check if a string is float?

try{
 Double.parseDouble(strVal);
}catch(NumberFormatException e){
 //My Logic         


        

Answer 1

Below is performance test to see the performance difference between regular expression VS try catch for validating a string is numeric.

Below table shows stats with a list(100k) with three points (90%, 70%, 50%) good data(float value) and remaining bad data(strings).

                      **90% - 10%   70% - 30%   50% - 50%**
**Try Catch**           87234580    122297750   143470144
**Regular Expression**  202700266   192596610   162166308

Performance of try catch is better (unless the bad data is over 50%) even though try/catch may have some impact on performance. The performance impact of try catch is because try/catch prevents JVM from doing some optimizations. Joshua Bloch, in "Effective Java," said the following:. Joshua Bloch, in "Effective Java," said the following:

• Placing code inside a try-catch block inhibits certain optimizations that modern JVM implementations might otherwise perform.

public class PerformanceStats {
static final String regularExpr = "([0-9]*[.])?[0-9]+";

public static void main(String[] args) {

    PerformanceStats ps = new PerformanceStats();
    ps.statsFinder();
    //System.out.println("123".matches(regularExpr));

}


private void statsFinder() {
    int count =  200000;
    int ncount = 200000;
    ArrayList ar = getList(count, ncount);

    System.out.println("count = " + count + " ncount = " + ncount);

    long t1 = System.nanoTime();
    validateWithCatch(ar);
    long t2 = System.nanoTime();
    validateWithRegularExpression(ar);
    long t3 = System.nanoTime();

    System.out.println("time taken with Exception          " + (t2 - t1) );
    System.out.println("time taken with Regular Expression " + (t3 - t2) );
}


private ArrayList getList(int count, int noiseCount) {
    Random rand = new Random();

    ArrayList list = new ArrayList();
    for (int i = 0; i < count; i++) {
        list.add((String) ("" + Math.abs(rand.nextFloat())));
    }
    // adding noise
    for (int i = 0; i < (noiseCount); i++) {
        list.add((String) ("sdss" + rand.nextInt() ));
    }
    return list;
}



private void validateWithRegularExpression(ArrayList list) {
    ArrayList ar = new ArrayList<>();
    for (String s : list) {
        if (s.matches(regularExpr)) {
            ar.add(Float.parseFloat(s));
        }
    }
    System.out.println("the size is in regular expression " + ar.size());
}

private void validateWithCatch(ArrayList list) {
    ArrayList ar = new ArrayList<>();
    for (String s : list) {
        try {
            float e = Float.parseFloat(s);
            ar.add(e);
        } catch (Exception e) {
        }
    }
    System.out.println("the size is in catch block " + ar.size());
}

}