java - Where to start in building an app/system that compresses and decompresses a file -


i'm developing application in java/android allows user compress , decompress files. @ first, started study file size such as:

1byte = 8bits 1kb = 1024byte 1mb = 1024kb 1gb = 1024mb 1tb = 1024gb 1pb = 1024tb 1eb = 1024pb 1zb = 1024eb 1yb = 1024zb

after studied this, studied , read articles on net , found out there 2 types of file compression (correct me if i'm wrong): lossless , lossy. lossless compression means file compressed smaller bit without losing single file while lossy compression means important files being removed while compressing file.

i read compression(run-length coding method) this:

aaabbccdffffeeeeh

to this:

3a2b2cd4f4eh

which gives me idea on how compressing/decompressing works on file.

i searched net there api compressing file on java(also applicable on android) is

java.util.zip

i tried codes on compressing , decompressing file various helpful websites/forum/etc (including stackoverflow.com) gives me experience study.

i read algorithms used in data compression are

 huffman encoding algorithm -  assigns code characters in file based on how characters occur  run-length encoding - generates two-part value repeated characters: first part specifies number of times character repeated, , second part identifies character  lempel-ziv algorithm - converts variable-length strings fixed-length codes consume less space original strings.

now, need know how code algo in compressing , decompressing file using java.util.zip(i don't know how use it. tutorials on net not working me :/). algo winzip, winrar, compressed folder(windows), , androzip(android app) using? please teach me step step(treat me unschooled person) on how java.util.zip works , different algorithms. sorry long post folks. future , posts(if there be)!

public static final byte[] unzip(byte[] in) throws ioexception { // decompress using gzipinputstream  bytearrayoutputstream outstream =    new bytearrayoutputstream(expected_compression_ratio * in.length);  gzipinputstream instream =    new gzipinputstream ( new bytearrayinputstream(in) );  byte[] buf = new byte[buf_size]; while (true) {   int size = instream.read(buf);   if (size <= 0)      break;   outstream.write(buf, 0, size); } outstream.close();  return outstream.tobytearray(); }   public static final byte[] zip(byte[] in) { try {   // compress using gzipoutputstream    bytearrayoutputstream byteout=      new bytearrayoutputstream(in.length / expected_compression_ratio);    gzipoutputstream outstream= new gzipoutputstream(byteout);    try {     outstream.write(in);   } catch (exception e) {     log.error("", e);   }    try {     outstream.close();   } catch (ioexception e) {       log.error("", e);   }    return byteout.tobytearray();  } catch (ioexception e) {     log.error("", e);   return null; } }

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