Question

Let’s consider the following code snippet in Java. There are some of possible approaches (that I know) to parse a String value to other numeric types (Let’s say for the sake of simplicity, it is an Integer, a wrapper type in Java).

package parsing;

final public class Parsing
{
    public static void main(String[] args)
    {
        String s="100";

        Integer temp=new Integer(s);
        System.out.print("\ntemp = "+temp);

        temp=Integer.parseInt(s);
        System.out.print("\ntemp = "+temp);        

        temp=Integer.valueOf(s).intValue();
        System.out.print("\ntemp = "+temp);

        temp=Integer.getInteger(s);
        System.out.print("\ntemp = "+temp);
    }    
}

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In all the cases except the last one, returns the value 100 after converting it into an Integer. Which one is the best approach to parse a String value to other numeric types available in Java? The last case returns NULL even if the String object s already contains a parsable value. Why?

Answer 1

Calling Integer.getInteger("42") attempts to fetch the value of the system property whose name is “42”. Unless you really do have a system property with that name, it will return null.

Here is the Java 7 javadoc if you want more details.

Yes, the name of the method is misleading, and its utility is questionable.

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FWIW, I’d use Integer.parseInt(String) if I required an int result and Integer.valueOf(String) if I required an Integer. I’d only use new Integer(String) if I required the object to be a new Integer and not one that might be shared.

(The reasoning is the same as for new Integer(int) versus Integer.valueOf(int). Again, read the javadocs for a more complete explanation.)