https://dl.acm.org/doi/pdf/10.1145/2983990.2984004

UnsoundTypeBreakage.java

package not.hub.test;

class UnsoundTypeBreakage<T, U> {

    final Constrain<? super T> constrain;
    final U u;

    UnsoundTypeBreakage(T t) {
        u = coerce(t);
        constrain = getConstrain();
    }

    public static void main(String[] args) {
        String zero = new UnsoundTypeBreakage<Integer, String>(0).u;
    }

    <B extends U>

    U upcast(Constrain<B> constrain, B b) {
        return b;
    }

    U coerce(T t) {
        return upcast(constrain, t);
    }

    Constrain<? super T> getConstrain() {
        return constrain;
    }

    class Constrain<B extends U> {
    }

}