Regular expression to compare numbers

[chandrajeet padhy]

I have a method

compare(Object value, String searchTxt);

The value can either be a Number, Date, String.
The searchTxt can have values to compare Strings, Dates, Numbers. It also can have logical comparison operators like =, !=, >, <, >=, <= eg.

compare(numValue, "> 1000 <= 2000)

compare(dateValue, "> 2006/12/12 <= 2007/01/25)

compare(stringValue, "> abc <= xyz )

Can I have some regular expression to control this comparision and make my life little easier. Because spliting the string and checking for all possible options can be a tedious job.

Peace n Regards

[chandrajeet padhy]

The searchTxt can have values like

"> 1000 <= 2000"

"> 2006/12/12 <= 2007/01/25"

"> abc <= xyz"

But I can check for the instanceof for the "value" and know that the searchTxt contains logical opearators plus (only Number or only Date or only String).

The real requirement is to comare the "value" according to the search string.

Say for eg:
if the method compare is invoked as compare(200, ">=100<500") it should return true

if the method compare is invoked as compare("xyz", ">=abc<xxx") it should return false

and so on...>

[Stan James]

I think you're stuck with splitting the string into tokens and processing each token. You're lucky in that your syntax is really simple

operator value [ operator value ... ]

And you're right, the code to test the object type, then test each token can be annoyingly boring and repetitive. I'd be tempted to build a swarm of little tiny classes - only a few lines each - to execute the operations.

Map operations = getOperationsFor( inputobject class name ) 
boolean ret = true
while more tokens
   operator = next token
   value = next token
   operation = operations.get( operator )
   ret = ret AND operation.compare( inputobject, value )
end while

An operation might look like:

class DateGT
{
   compare( object input, String value )
   {
      Date d1 = (Date)input;
      Date d2 = makeDateFrom(value); 
      return d1.compareTo(d2) > 0;
   }
}

Did that make sense? I bet you could build this with not one "if" test. Could be lost o fun.

[Stefan Wagner]

Perhaps if you transform:

compare (x, "op1 val1 op2 val2")

to

x op1 val1 && x op2 val2

and invoke a scripting engine like beanshell, to evaluate the expression?

[chandrajeet padhy]

Hi James,
Can you give an example in java please

[Jim Yingst]

[chandrajeet padhy ]:

I have a method

compare(Object value, String searchTxt);

From what you say later, I think it might make a lot more sense to instead make three methods:

compare(String value, String searchTxt)
 
compare(Number value, String searchTxt)
 
compare(Date value, String searchTxt)

And if you must, you can have an Object version:

compare(Object value, String searchTxt) {
    if (value instanceof String)
        return compare((String) value, searchText);
    if (value instanceof Number)
        return compare((Number) value, searchText);
    if (value instanceof Date)
        return compare((Date) value, searchText);
    throw new IllegalArgumentException("Can't compare class " + value.getClass());
}

Within each of the other three methods, you will know whether you're dealing with a String, Number or Date, making the code in each individual method simpler.

[Ilja Preuss]

Do those searchTxt objects *need* to be Strings? Where are they coming from?

[chandrajeet padhy]

Hi Jim Yingst,

I dont have difficulty in identifying Date, Number or String.

My problem is actually inside the compare method. How can I?
As I said The searchText is a tuff thing. And James got it right. But I need a java based solution.

[Stan James]

See if you can translate my babble into Java ... one line at a time should do it. We try to give really good hints here, but not complete solutions. If you take the effort to make some almost working code, we'll help you move it along. So jump in ... it's a lot more fun if you make it work yourself.

[chandrajeet padhy]

I made it work this way. Any suggestions for improvement is welcomed.

                if(element instanceof Number){
                    return ValueComparator.compare((Number) element, parts );
                }
                else if(element instanceof Calendar){
                    return ValueComparator.compare(((Calendar) element).getTime(), parts );
                }else if(element instanceof String){
                    return ValueComparator.compare((String) element, parts );
                }    

ValueComparator looks as:-

 public class ValueComparator
{
    static HashMap<String, Operation> oprations;
    private static String LOGICAL_OPERATORS = new String("&, |");
    public static boolean compare(Number element, String[] parts){
        Operation operation;
        boolean ret = true;
        int i=0;
        String operator, value;
        while(i<parts.length){
           operator = parts[i];
//           if(LOGICAL_OPERATORS.contains(operator)){
//               i++;
//               continue;
//           }
           value = parts[i+1];
           operation = oprations.get( operator.trim() );
           if(operation != null)
               ret = ret && operation.compare( element, new Double(value) );
           i+=2;
        }
        return ret;
    }
    private static SimpleDateFormat dateFormatter = new SimpleDateFormat();
    public static boolean compare(Date element, String[] parts){
        //to be implemented
        return false;
    }
    public static boolean compare(String element, String[] parts){
//to be implemented
        return false;
    }
    static{
        oprations =  new HashMap<String, Operation>();
        oprations.put( ">", new GreaterThan());
        oprations.put( "<", new LessThan());
        oprations.put( "=", new EqualsTo());
        oprations.put( "!=", new NotEQ());
        oprations.put( ">=", new GreaterThanEQ());
        oprations.put( "<=", new LessThanEQ());
    }
}   

And then different operations as per:

 public interface Operation
{
    public boolean compare( Number gridElement, Number inputValue );
 
    public boolean compare( Date gridElement, Date inputValue );
 
    public boolean compare( String gridElement, String inputValue );
}   

Thanks

[Stan James]

Kool. I bet you can generalize a bit more yet. Just playing thought experiments here - you can decide if it's worth trying. What if the interface for Operation was still two objects?

public boolean compare( Object gridElement, Object inputValue );

Then the Operation would have to get the two arguments into the proper format itself. That seems like a good place to create a date or a number. An abstract DateOperation could do the date manipulation and call an abstract compare( Date, Date ) method.

Your map of operations might include the type:

operations.put( "Date.>", new DateGreaterThan());
operations.put( "Number.>", new NumberGreaterThan());

That would multiply the number of operations to types*operators. Ick. Maybe we could cut back to one operator class per type:

oprations.put( "Date.>", new DateOperation(false, false, true));

where the arguments tell what to return if the standard compareTo() returns <0, 0 or >0.

Any of that sound fun?

[chandrajeet padhy]

Oh yea. I thought of that to have only one method compare(obj, obj) in the Operation interface. But, that will lead upto creating types*operators number of classes like DateGT, DateLT, DateGEQ, DateLEQ, NumberGT, NumberLT...so on.
I just kept it simiplified to have only few Operation impls to handle all data types. Great going! Thanks again.