Task: Base64 encode data
C++: #include <iostream>
#include <fstream>
#include <vector>

typedef unsigned char byte;
using namespace std;

const unsigned m1 = 63 << 18, m2 = 63 << 12, m3 = 63 << 6;

class base64
{
public:
    base64() { char_set = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"; }
    string encode( vector<byte> v )
    {
	string res;
	unsigned d, a = 0, l = static_cast<unsigned>( v.size() );
	while( l > 2 )
	{
	    d = v[a++] << 16 | v[a++] << 8 | v[a++];	
	    res.append( 1, char_set.at( ( d & m1 ) >> 18 ) );	
	    res.append( 1, char_set.at( ( d & m2 ) >> 12 ) );	
	    res.append( 1, char_set.at( ( d & m3 ) >>  6 ) );
	    res.append( 1, char_set.at( d & 63 ) );
	    l -= 3;
	}
	if( l == 2 )
	{
	    d = v[a++] << 16 | v[a++] << 8;
	    res.append( 1, char_set.at( ( d & m1 ) >> 18 ) );	
	    res.append( 1, char_set.at( ( d & m2 ) >> 12 ) );	
	    res.append( 1, char_set.at( ( d & m3 ) >>  6 ) );
	    res.append( 1, '=' );
	}
	else if( l == 1 )
	{
	    d = v[a++] << 16;
	    res.append( 1, char_set.at( ( d & m1 ) >> 18 ) );	
	    res.append( 1, char_set.at( ( d & m2 ) >> 12 ) );	
	    res.append( "==", 2 );
	}
	return res;
    }

private:
    string char_set;
};

int main( int argc, char* argv[] )
{
    base64 b;
    basic_ifstream<byte> f( "favicon.ico", ios::binary );
    string r = b.encode( vector<byte>( ( istreambuf_iterator<byte>( f ) ), istreambuf_iterator<byte>() ) );
    copy( r.begin(), r.end(), ostream_iterator<char>( cout ) );
    return 0;
}

Java: import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
import java.net.URLConnection;
import java.util.Arrays;

public class Base64 {

    private static final char[] alpha = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/".toCharArray();

    static String base64(InputStream is) throws IOException {
        StringBuilder sb = new StringBuilder();
        int blocks = 0;

        while (true) {
            int c0 = is.read();
            if (c0 == -1)
                break;
            int c1 = is.read();
            int c2 = is.read();

            int block = ((c0 & 0xFF) << 16) | ((Math.max(c1, 0) & 0xFF) << 8) | (Math.max(c2, 0) & 0xFF);

            sb.append(alpha[block >> 18 & 63]);
            sb.append(alpha[block >> 12 & 63]);
            sb.append(c1 == -1 ? '=' : alpha[block >> 6 & 63]);
            sb.append(c2 == -1 ? '=' : alpha[block & 63]);

            if (++blocks == 19) {
                blocks = 0;
                sb.append('\n');
            }
        }

        if (blocks > 0)
            sb.append('\n');

        return sb.toString();
    }

    private static void assertBase64(String expected, byte[] bytes) throws IOException {
        String actual = base64(new ByteArrayInputStream(bytes));
        if (!actual.equals(expected)) {
            throw new IllegalStateException(String.format("Expected %s for %s, but got %s.",
                    expected, Arrays.toString(bytes), actual));
        }
    }

    private static void testBase64() throws IOException {
        assertBase64("", new byte[]{});
        assertBase64("AA==\n", new byte[]{0});
        assertBase64("AAA=\n", new byte[]{0, 0});
        assertBase64("AAAA\n", new byte[]{0, 0, 0});
        assertBase64("AAAAAA==\n", new byte[]{0, 0, 0, 0});
        assertBase64("/w==\n", new byte[]{-1});
        assertBase64("
        assertBase64("
        assertBase64("
    }

    public static void main(String[] args) throws IOException {
        testBase64();

        URLConnection conn = new URL("http:
        conn.addRequestProperty("User-Agent", "Mozilla"); 
        try (InputStream is = conn.getInputStream()) {
            System.out.println(base64(is));
        }
    }
}