How covariant list allows the blocked operations.

DemoClass.java

package com.tutorials.vishal;

import com.tutorials.vishal.hierarchy.BaseWork;
import com.tutorials.vishal.hierarchy.RxWork;
import com.tutorials.vishal.hierarchy.Scheduler;

import java.util.ArrayList;
import java.util.List;

public class DemoClass {

    void driver() {
        List<BaseWork> baseWorks = new ArrayList<>();
        List<RxWork> rxWorks = new ArrayList<>();
        
        baseWorks.add(new RxWork());
        baseWorks.add(new BaseWork());
        
        startJob(baseWorks); // Bingo!
        startJob(rxWorks);
    }

    void startJob(List<? extends BaseWork> incomingWork) {
        // validate the work and submit.
        for (BaseWork b : incomingWork) {
            Scheduler.submit(b);
        }
    }
}