Files.java

abstract class Files {
    public <R extends Readable & Closeable> void copy(InputSupplier<R> from) {
        CharStreams.copy(from, newWriterSupplier());
    }

    public <W extends Appendable & Closeable> void copy(OutputSupplier<W> to) {
        CharStreams.copy(newReaderSupplier(), to);
    }

    abstract OutputSupplier<OutputStreamWriter> newWriterSupplier();

    abstract InputSupplier<InputStreamReader> newReaderSupplier();
}