How to design an execution engine for a sequence of tasks

Question

I am trying to code a problem in Java where I have to execute a bunch of tasks.

Problem

Execute a job which consists of multiple tasks and thos

Answer 1

Abstracting from the multithreading

class TaskA{
    SimpleTask Y;
    SimpleTask Z;

    SimpleTask PJ;
    SimpleTask RJ;

    Run(){
        // do the partial job
        PJ.Run();
        Y.Run();
        // do the remaining job
        RJ.Run();
        Z.Run();
        // return;
    }
} 

class TaskB{
    TaskA P;
    SimpleTask J;

    Run(){
        // do the job
        J.Run();
        P.Run();
        // return;
    }
}