Want to check what list contains

Question

I have a list with datatype "string" But I want to check whether it contains number as a string or not.

Answer 1

Use the isNumeric() method on the strings.

for (String s : strings) {
    if (s.countMatches('.') <= 1) {
        system.debug(s.remove('.').isNumeric());
    } else system.debug(false);
}

Answer 2

Create a Set of Strings which will contain all the elements from the list:

List <String> myList = new List <String> {'1', '2', '3', '2'};
Set <String> mySet = new Set <String> ();
mySet.addAll(myList);

which will remove any duplicates.

Then you can convert your number into a string and check whether the set contains it by using the contains method:

if (mySet.contains(String.valueOf(1))) 
{
    // do something 
}

The other option is to cast the number to a string and then iterate through the List of Strings until you find it:

List <String> myList = new List <String> {'1', '2', '3', '2'};
String myNumberAsString = String.valueOf(3);
Boolean numberFound = false;

for (String listItem : myList)
{
    if (listItem == myNumberAsString)
    {
        numberFound = true;
        break;
    }
}

if (numberFound)
{
    // do something
}

Answer 3

You can make use of instanceOf method to compare and find what kind of value the list is storing.

instanceOf - If you need to verify at run time whether an object is actually an instance of a particular class, use the instanceof keyword.

So if you just want to verify if the element within your list of strings is a number(Integer/Decimal) or not, you can make use of instanceOf Integer or instanceOf Decimal

For eg:

List <String> myList = new List <String> {'1.0', 'aajcka', '3.35', '2'};
List<Integer> indexesofElementsAsNumber = new List<Integer>();

for(Integer i=0; i < myList.size(); i++){
    try{
        Object o = Decimal.valueOf(myList[i]);
        Boolean b =  o instanceof Decimal;
        if(b){
              indexesofElementsAsNumber.add(i);
        }
    }
    catch(TypeException te){
         continue;
    }           
}
system.debug('=====List of indexes that contain nummbers===='+indexesofElementsAsNumber);

The above code gives me below output:

=====List of indexes that contain nummbers====(0, 2, 3)

PS: There is a need to make the use of Object class while you do the comparision because if you do Integer.valueOf() instance of Integer will throw error saying Integer is always an instance of Integer.