How to create different activities in a workflow?

Defines an activity class and how to create multiple activity class instances in a workflow.

Can you give more info or some sample code you might have?

Each method in your ActivityInterface is an activity. You can create multiple activity stubs in your workflow code.

I have a parent workflow A. Under A, an activity runs tasks D, C, and D asynchronously. However, tasks B, C, and D are independent of each other. How to ensure that the variables obtained by B, C, and D from @QueryMethod in the activity do not affect each other?

That is, how to ensure the availability of variables in a task when four tasks are executed asynchronously under an activity ?

Temporal activities cannot invoke other activities. They also cannot have query methods.

Are you confusing activities with workflows?