++ All future methods and Batch Classes are Asynchronous and we can not call an Asynchronous call from and Asynchronous call. But to Take control of your asynchronous Apex processes by using the Queueable interface. This interface enables you to add jobs to the queue and monitor them, Future methods can’t be used in Visualforce controllers in getMethodName(), setMethodName(), nor in the constructor. You can’t call a future method from a future method. Nor can you invoke a trigger that calls a future method while running a future method. Using @future annotations, your method execute the callout when your salesforce has resources available.You can call future method for long operations such as web services because future method runs in background asynchronously.Use the future annotations when making a asynchronous callouts to the external service. Refer the below link:- To avoid a Mixed DML error, I must use @future method to change the non-user record, which then would ideally trigger the Batch method to handle the large amount of records that will be changed. The ability to call Batch from @future would be great. Or remove the Mixed DML limitation on user records.
2) You cannot call another future method from a future method. As per Salesforce documentation, You cannot call a method annotated with future from a method that also has the future annotation. Nor can you call a trigger from an annotated method that calls another annotated method. If you do not have dependency between f1 & f2, you can call both methods one by one from original class. Future methods can’t be used in Visualforce controllers in getMethodName(), setMethodName(), nor in the constructor. You can’t call a future method from a future method. Nor can you invoke a trigger that calls a future method while running a future method. The reason why sObjects can’t be passed as arguments to future methods is because the sObject might change between the time you call the method and the time it executes. In this case, the future method will get the old sObject values and might overwrite them. A future call allows Apex code to kick off some other Apex code that will run later, and then the current transaction can continue without waiting for that other code to complete. One worry when trying to do future calls is that there is a limit to the number of future calls based on your number of licenses or an org minimum of 250,000.
Yes, future method can be invoked from Trigger. Many examples: https://salesforce.stackexchange.com/questions/173444/help-with-calling-future-method-from-trigger A future method runs in the background, asynchronously. You can call a future method for executing long-running operations, such as callouts to external Web services or any operation you’d like to run in its own thread, on its own time. Yes, we can’t call future method from batch class. You cannot normally call a future method in another future method, but if your salesforce license has the pilot feature enabled then you can call a future method from another future method. To get the pilot feature you ll need to contact the salesforce where you can also double or triple some governor limits of asynchronous apex in your org.
You can neither call a method annotated with future from a method that also has the future annotation, nor call a trigger from an annotated method that calls
28 Dec 2017 First, using a future call tells the platform to wait and process the method at the next convenient time for the platform. Remember that Salesforce You can't call another future method from a future method. As per Salesforce documentation, You can't call a method annotated with the future from a method that also has the future annotation. Nor can you call a trigger from an annotated method that calls another annotated method. If you do not have a dependency between f1 & f2, you can call both methods one by one from the original class.