Most efficient way of converting String to Integer in java

Question

There are many ways of converting a String to an Integer object. Which is the most efficient among the below:

Integer.valueOf()
Integer.parseInt()
org.apache.commons.beanutils.converters.IntegerConverter

My usecase needs to create wrapper Integer objects...meaning no primitive int...and the converted data is used for read-only.

Solution 1

Don't even waste time thinking about it. Just pick one that seems to fit with the rest of the code (do other conversions use the .parse__() or .valueOf() method? use that to be consistent).

Trying to decide which is "best" detracts your focus from solving the business problem or implementing the feature.

Don't bog yourself down with trivial details. :-)

On a side note, if your "use case" is specifying java object data types for your code - your BA needs to step back out of your domain. BA's need to define "the business problem", and how the user would like to interact with the application when addressing the problem. Developers determine how best to build that feature into the application with code - including the proper data types / objects to handle the data.

Solution 2

If efficiency is your concern, then creating an Integer object is much more expensive than parsing it. If you have to create an Integer object, I wouldn't worry too much about how it is parsed.

Note: Java 6u14 allows you to increase the size of your Integer pool with a command line option -Djava.lang.Integer.IntegerCache.high=1024 for example.

Note 2: If you are reading raw data e.g. bytes from a file or network, the conversion of these bytes to a String is relatively expensive as well. If you are going to write a custom parser I suggest bypassing the step of conversing to a string and parse the raw source data.

Note 3: If you are creating an Integer so you can put it in a collection, you can avoid this by using GNU Trove (trove4j) which allows you to store primitives in collections, allowing you to drop the Integer creation as well.

Ideally, for best performance you want to avoid creating any objects at all.

Solution 3

Your best bet is to use Integer.parseInt. This will return an int, but this can be auto-boxed to an Integer. This is slightly faster than valueOf, as when your numbers are between -128 and 127 it will use the Integer cache and not create new objects. The slowest is the Apache method.

private String data = "99";

public void testParseInt() throws Exception {
    long start = System.currentTimeMillis();
    long count = 0;
    for (int i = 0; i < 100000000; i++) {
        Integer o = Integer.parseInt(data);
        count += o.hashCode();
    }
    long diff = System.currentTimeMillis() - start;
    System.out.println("parseInt completed in " + diff + "ms");
    assert 9900000000L == count;
}

public void testValueOf() throws Exception {
    long start = System.currentTimeMillis();
    long count = 0;
    for (int i = 0; i < 100000000; i++) {
        Integer o = Integer.valueOf(data);
        count += o.hashCode();
    }
    long diff = System.currentTimeMillis() - start;
    System.out.println("valueOf completed in " + diff + "ms");
    assert 9900000000L == count;
}


public void testIntegerConverter() throws Exception {
    long start = System.currentTimeMillis();
    IntegerConverter c = new IntegerConverter();
    long count = 0;
    for (int i = 0; i < 100000000; i++) {
        Integer o = (Integer) c.convert(Integer.class, data);
        count += o.hashCode();
    }
    long diff = System.currentTimeMillis() - start;
    System.out.println("IntegerConverter completed in " + diff + "ms");
    assert 9900000000L == count;
}

parseInt completed in 5906ms
valueOf completed in 7047ms
IntegerConverter completed in 7906ms

Solution 4

I know this isn't amongst your options above. IntegerConverter is ok, but you need to create an instance of it. Take a look at NumberUtils in Commons Lang:

Commons Lang NumberUtils

this provides the method toInt:

static int toInt(java.lang.String str, int defaultValue) 

which allows you to specify a default value in the case of a failure.

NumberUtils.toInt("1", 0)  = 1

That's the best solution I've found so far.

Solution 5

I'm always amazed how quickly many here dismiss some investigation into performance problems. Parsing a int for base 10 is a very common task in many programs. Making this faster could have a noticable positive effect in many environments.

As parsing and int is actually a rather trivial task, I tried to implement a more direct approach than the one used in the JDK implementation that has variable base. It turned out to be more than twice as fast and should otherwise behave exactly the same as Integer.parseInt().

public static int intValueOf( String str )
{
    int ival = 0, idx = 0, end;
    boolean sign = false;
    char ch;

    if( str == null || ( end = str.length() ) == 0 ||
       ( ( ch = str.charAt( 0 ) ) < '0' || ch > '9' )
          && ( !( sign = ch == '-' ) || ++idx == end || ( ( ch = str.charAt( idx ) ) < '0' || ch > '9' ) ) )
        throw new NumberFormatException( str );

    for(;; ival *= 10 )
    {
        ival += '0'- ch;
        if( ++idx == end )
            return sign ? ival : -ival;
        if( ( ch = str.charAt( idx ) ) < '0' || ch > '9' )
            throw new NumberFormatException( str );
    }
}

To get an Integer object of it, either use autoboxing or explicit

Interger.valueOf( intValueOf( str ) ).

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