ExceptionUnions.java

package com.benjiweber.example;

import java.util.Random;

public class ExceptionUnions {

    public static void main(String... args) {
        try {
            foo().check();
        } catch (Eint eint) {
            System.out.println("eint " + eint.i);
        } catch (EString eString) {
            System.out.println("estring " + eString.s);
        }

        Either<Eint,Edouble> x = () -> new Edouble(5.5);
        try {
            x.check();
        } catch (Edouble e) {
            System.out.println("double " + e.d);
        } catch (Eint e) {
            throw new IllegalStateException("Won't be");
        }
    }

    public static Either<Eint, EString> foo() {
        // return () -> new Edouble(4.4); // compile failure
        return new Random().nextBoolean()
            ? () -> new Eint(4)
            : () -> new EString("blah");
    }

    interface Either<E1 extends E, E2 extends E> {
        void check() throws E1, E2;
    }

    static class E extends Exception {
        public Throwable fillInStackTrace() {
            return this;
        }
    }

    static class EString extends E {
        String s;

        EString(String s) throws EString {
            this.s = s;
            throw this;
        }
    }

    static class Eint extends E {
        int i;

        Eint(int i) throws Eint {
            this.i = i;
            throw this;
        }
    }

    static class Edouble extends E {
        double d;

        Edouble(double d) throws Edouble {
            this.d = d;
            throw this;
        }
    }

}