Use Type class to call parameterized constructor

Question

Using this to get below working:

    public class t12345 implements Database.Batchable<sObject> {

        String query;
        Boolean xyz;

        public t12345(String query){
            this.query= query;
        }

public Database.QueryLocator start(Database.BatchableContext bC){      
    return Database.getQueryLocator(query);
}
    }

and when I run below from developer console,

    Type api = Type.forName('t12345');
    Object apiCall = JSON.deserialize('{"query":"hello world"}',api);
Database.executeBatch((Database.Batchable<sObject>) apiCall);

above execution results in error Argument 1 cannot be null which is coming from start method of batch where query value is still null as constructor with query is not invoked

Answer 1

If you try:

MyClass instance = new MyClass(); // or any other approach to construction
Database.executeBatch((Database.Batchable<Account>)instance);

You should get this error:

System.TypeException: Invalid conversion from runtime type MyClass to Database.Batchable

If you want to cast a class to Database.Batchable<SObject>, it has to implement that interface.

Instead of:

public class MyClass { ... }

Use:

public class MyClass implements Database.Batchable<SObject> { ... }

This adjustment will mean you actually have to define the methods enforced by that interface.

Answer 2

You cannot generically call a non-no-argument constructor. While other object-oriented languages have methods for doing this, Apex Code does not have any support for this.

Answer 3

Your JSON.deserialize will (probably) set the fields but not via the constructor you have the System.debug in. (Constructors can have an arbitrary signature but the field names are effectively a fixed signature.)