Java Generics: chaining together generic function object

Question

I\'ve been struggling with the following problem. I have a series of function objects, each with it\'s own input and output types defined via generic type arguments in java. I w

Answer 1

Here's a way to do it. The run method is not typesafe, but given that the only way to append a pipe is to do it in a type-safe way, the whole chain is type-safe.

public class Chain {
    private List> pipes;

    private Chain() {
    }

    public static  Chain start(Pipe pipe) {
        Chain chain = new Chain();
        chain.pipes = Collections.>singletonList(pipe);;
        return chain;
    }

    public  Chain append(Pipe pipe) {
        Chain chain = new Chain();
        chain.pipes = new ArrayList>(pipes);
        chain.pipes.add(pipe);
        return chain;
    }

    @SuppressWarnings({ "rawtypes", "unchecked" })
    public T run(S s) {
        Object source = s;
        Object target = null;
        for (Pipe p : pipes) {
            target = p.transform(source);
            source = target;
        }
        return (T) target;
    }

    public static void main(String[] args) {
        Pipe pipe1 = new Pipe() {
            @Override
            public Integer transform(String s) {
                return Integer.valueOf(s);
            }
        };
        Pipe pipe2 = new Pipe() {
            @Override
            public Long transform(Integer s) {
                return s.longValue();
            }
        };
        Pipe pipe3 = new Pipe() {
            @Override
            public BigInteger transform(Long s) {
                return new BigInteger(s.toString());
            }
        };
        Chain chain = Chain.start(pipe1).append(pipe2).append(pipe3);
        BigInteger result = chain.run("12");
        System.out.println(result);
    }
}