APEX: Use a dynamic string to create an instance of a class

2.7K Asked by behail_3566 in Salesforce , Asked on Jul 19, 2021

I have an abstract class called Process that I extend to create a list of processes (List); each in relation to an object. For now everything works as expected but I'm really hoping to create a very dynamic approach to these processes. For example I also have a Process__c custom object, and with a SOQL statement I can get a list of all the Process_c records I need for a given context. These records contain the String name of a class that I want to instantiate, but for the life of me I can't seem to find a way to do this.

I've tried something like the following:

String s = 'Account'; List activeProcesses = [SELECT Name FROM Process__c WHERE Active__c = TRUE AND Object__c = :s]; List processNames = Utils.Data.Convert.stringList(activeProcesses, 'Name'); Type t = Type.forName('Process'); List processes = new List(); for(String processName : processNames){ Process p = t.newInstance(processName); processes.add(p); }

The error I'm getting when attempting this is: Method does not exist or incorrect signature: [Type].newInstance(String) I really hope the harsh reality isn't that this is just not possible but if it is I need to know that as well, so any insight you have with this question would be greatly appreciated.

Answered by Bhaanumati shukla

Your strategy will work to solve apex string class, but your constructor must contain no parameters, and the same goes for your newInstance() call. You pass the name of the Type you want to construct into the Type.forName method.

Type customType = Type.forName('SomeClass'); SomeClass instance = (SomeClass)customType.newInstance();

You probably will want to implement an interface here as well. Something like:

public interface IProcess { void execute(); } public class Process1 { public Process1() { // instantiation logic } public void execute() { // execution logic } }

You would use the above as follows:

IProcess instance = (IProcess)Type.forName('Process1').newInstance();

You don't even really need to cache it for simple cases:

(IProcess)Type.forName('Process1').newInstance().execute();

Your Answer

Answer (1)

Ranjana

In Salesforce Apex, creating an instance of a class dynamically using a string involves leveraging the Type class. This approach is useful when the class name is determined at runtime. Here’s how you can achieve this:

Steps to Dynamically Create an Instance of a Class in Apex

Class Names in String Form:

You start with the class name in string form.

  String className = 'MyClass';

Using the Type Class:

Use the Type.forName method to get the Type reference for the class.

Type t = Type.forName(className);

Instantiate the Class:

Create an instance of the class using the newInstance method of the Type class.

Object obj = t.newInstance();

Casting to the Appropriate Type:

Cast the object to the specific class type if you need to call methods on it.

MyClass instance = (MyClass) obj;

instance.myMethod();

Complete Example

Here’s a complete example demonstrating these steps:

public class DynamicInstanceCreator {

    public void createInstance() {

        // The class name is provided as a string

        String className = 'MyClass';

        // Get the Type reference

        Type t = Type.forName(className);

        // Create an instance of the class

        Object obj = t.newInstance();

        // Cast the object to the appropriate class

        MyClass instance = (MyClass) obj;

        // Call a method on the instance

        instance.myMethod();

    }

}

public class MyClass {

    public void myMethod() {

        System.debug('Method executed!');

    }

}

Handling Exceptions

Check Existence of the Class:

Handle cases where the class might not exist.

try {

    Type t = Type.forName(className);

    Object obj = t.newInstance();

} catch (TypeException e) {

    System.debug('Class not found: ' + e.getMessage());

}

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