Vanilla unsigned ints

Unisgned.java

package org.fesler.vanilla;

import java.io.*;

public enum Unsigned {;
    public static int add(int i, int j) {
        return i + j;
    }

    public static int subtract(int i, int j) {
        return i - j;
    }

    public static int multiply(int i, int j) {
        return i * j;
    }

    public static int shiftLeft(int i, int n) {
        return i << n;
    }

    public static int shiftRight(int i, int n) {
        return i >>> n;
    }

    public static int parseUnsignedInt(String text) {
        long tmp = Long.parseLong(text);
        return (((int) (tmp >> 1)) << 1) + ((int) (tmp & 1));
    }

    public static String toString(int n) {
        return Long.toString((((long) (n >>> 1)) << 1) + (n & 1));
    }

    // missing methods

    public static void writeUnsignedInt(DataOutputStream dos, int uint) throws IOException {
        dos.writeInt(uint);
    }

    public static int readUnsignedInt(DataInputStream dis) throws IOException {
        return dis.readInt();
    }

    public static void main(String... args) throws Exception {
        assert "2500000000".equals(toString(subtract(add(2000 * 1000 * 1000, 1750 * 1000 * 1000), 1250 * 1000 * 1000)));
        assert "2500000001".equals(toString(add(subtract(add(2000 * 1000 * 1000, 1750 * 1000 * 1000), 1250 * 1000 * 1000), 1)));
        assert "4000000000".equals(toString(multiply(1000 * 1000, 4000)));
        assert "3200000000".equals(toString(shiftLeft(100 * 1000 * 1000, 5)));
        assert "1000000000".equals(toString(shiftRight(parseUnsignedInt("4000000000"), 2)));

        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        DataOutputStream dos = new DataOutputStream(baos);
        writeUnsignedInt(dos, multiply(1000 * 1000, 4000));
        writeUnsignedInt(dos, parseUnsignedInt("3210000000"));
        dos.close();
        DataInputStream dis = new DataInputStream(new ByteArrayInputStream(baos.toByteArray()));
        assert "4000000000".equals(toString(readUnsignedInt(dis)));
        assert "3210000000".equals(toString(readUnsignedInt(dis)));
        dis.close();
    }

}

Solution to the puzzle presented here: http://vanillajava.blogspot.com/2012/01/unsigned-challenge.html