Apex : convert object to a list

apexlistobject

I have an object with value (s1,s2,s3,s4) (this is the value I get during System.debug).
Now I want to convert this values to list of strings, i.e ['s1','s2','s3','s4'].

How can I do that?

I tried,

List<String> test = new List<String>();
test.addAll((List<String>)obj); // threw an error cant convert List<Any> to List<String>

List<String> test = new List<String>();
test.addAll((List<String>) JSON.deserializeUntyped(obj.toString())); 
// throws Unexpected character ('(' (code 40)): expected a valid value (number, String,  array, object, 'true', 'false' or 'null') at input location [1,2]

EDIT:
In case you are wondering how I got the object.
The object is a list of strings I retrieved from the body during an API call, after converting to Map<String, Object> I get the above obj

Best Answer

Unfortunately apex doesn't handle list-level type conversion so if "obj" is a List<Object> and even if each Object is actually a String you still cannot convert that list directly to a List<String> via type casting.

You have two options. First is to do a loop:

List<Object> obj = ...;
List<String> objAsStrings = new List<String>();

for (Object value : obj) {
  objAsStrings.add((String) value);
}

Or you can try serializing and deserializing via JSON:

objAsStrings = (List<String>) JSON.deserialize(JSON.serialize(obj), List<String>.class);

Both will fail if not all entries in the obj are strings (the JSON approach will be more permissive, only failing with numeric and Boolean entries, since many other types are still expressed as string-like in JSON).

Both are relatively expensive, CPU wise, but the JSON approach costs more CPU time for smaller arrays. It wins when you get to large arrays.

Related Solutions

[SalesForce] Simple Apex class to return a list of strings

You can't instantiate a List like that using an integer. You don't need to explicitly specify how much items are going into the list when it is created. Instead, just remove the integer:

//Instantiate the list
String[] myArray = new List<String>();

You're logic in your loop seems to be incorrect as well. Specifically, myArray's size will always be 0 when you instantiate it. Change your loop logic to:

for(Integer i=0;i<length;i++) {
   // code
}

You want to generate a List of strings based on the i variable. You will want to change your internal logic to:

//Populate the array
myArray.add('Test ' + i);

// Write value to the debug log
System.debug(myArray[i]);

Finally, you want to return that Array. You need to change your method so the return type is no longer void by changing its signature:

public static String[] generateStringArray(Integer length)

then it is just a matter of returning that array at the end of your method:

return myArray;

This would bring it all together as:

public class StringArrayTest {
    //Public Method
    public static String[] generateStringArray(Integer length) {
        //Instantiate the list
        String[] myArray = new List<String>();

        //Iterate throught the list
        for(Integer i=0;i<length;i++) {
            //Populate the array
            myArray.add('Test ' + i);

            // Write value to the debug log
            System.debug(myArray[i]);
        } //end loop

        return myArray;
    }//end method       
}// end class

Some more info on Arrays and Lists, Loops, and Class methods for future reference.

[SalesForce] System.JSONException: Malformed JSON: Expected ‘[‘ at the beginning of List/Set when deserializing JSON object in apex

JSON arrays are simply written as '[ "Item1", "Item2", "Item3" ]'.

As for generating the correct array, you should be using JavaScript built-ins, instead of trying to write your own JSON by hand:

var inputs = [];
inputs.push("String 'One'")
inputs.push("String 'Two'")
inputs.push("String 'Three'")
document.getElementById('{!$Component.pageId.form.hiddenfield}').value = JSON.stringify(inputs);

Best Answer

Related Solutions

[SalesForce] Simple Apex class to return a list of strings

[SalesForce] System.JSONException: Malformed JSON: Expected ‘[‘ at the beginning of List/Set when deserializing JSON object in apex

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