Inheritance Polymorphism vs Interface Polymorphism

// Reader.java
public interface Reader {
    public String Read();
}

// StdinReader.java
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class StdinReader implements Reader {
    public String Read() {
        String input = "";
        try {
            BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
            input = br.readLine();
        } catch (IOException io) {
            io.printStackTrace();
        }
        return input;
    }
}

// Writer.java
public interface Writer {
    public void Write(String msg);
}

// StdoutWriter.java
public class StdoutWriter implements Writer {
    public void Write(String msg) {
        System.out.println(msg);
    }
}

// NetworkWriter.java
public class NetworkWriter implements Writer {
    private String _address;

    public NetworkWriter(String address) {
        _address = address;
    }

    public void Write(String msg) {
        System.out.println("Writing \"" + msg + "\" to: " + _address);
    }
}

// ReaderWriter.java
public class ReaderWriter implements Reader, Writer {
    Reader _reader;
    Writer _writer;

    public ReaderWriter(Reader r, Writer w) {
        _reader = r;
        _writer = w;
    }

    public String Read() {
        return _reader.Read();
    }

    public void Write(String msg) {
        _writer.Write(msg);
    }
}

// Main.java
public class Main {
    public static void Example(String exampleName, ReaderWriter rw) {
        rw.Write(exampleName);
        rw.Write("-------------------------------------");
        rw.Write("Enter some text below:");
        String someText = rw.Read();
        rw.Write("You entered: \"" + someText + "\"\n");
    }

    public static void main(String[] args) {
        Writer w = new StdoutWriter();
        Reader r = new StdinReader();
        Writer nw = new NetworkWriter("localhost:8080");

        Example("StdinReader and StdoutWriter example:", new ReaderWriter(r, w));
        Example("StdinReader and NetworkWriter example:", new ReaderWriter(r, nw));
    }
}