Question

I have a byte array and create string from it using new String(array). When I convert it back to a byte array using .getBytes(), it doesn’t give me the original byte array back. What gives?

String text = "two hats";
boolean t1 = Arrays.equals(text.getBytes(), text); // true

byte[] barray = {(byte)0x8f, (byte)0xd5, (byte)0xaf, (byte)0x30, (byte)0xb9};        

String test1 = new String(barray); 
boolean t2 = Arrays.equals(barray.getBytes(), test1); // false

// I tried setting an encoding but that didn't help.

Charset cs = Charset.forName("UTF-8"); 
String test2 = new String(barray, cs);       
boolean t3 = Arrays.equals(barray, test2, cs); // false

Here’s the code I am actually using.

// test byte array vs string
public static void testEqual(byte[] bytes, String str) {
    byte[] fromString = str.getBytes();        

    printBytes(bytes);        
    printBytes(fromString);        
    System.out.println(Arrays.equals(bytes, fromString));        
}

// test byte array vs string, with charset
public static void testEqual(byte[] bytes, String str, Charset charset) {
    byte[] fromString = str.getBytes(charset);        

    printBytes(bytes);        
    printBytes(fromString);        
    System.out.println(Arrays.equals(bytes, fromString));
}

// prints bytes as hex string
public static void printBytes(byte[] bytes) {
    for (byte b: bytes) {
        System.out.print(String.format("%02X ", b));
    }        
    System.out.println();
}

public static void main(String[] args) {
    String text = "two hats";
    testEqual(text.getBytes(), text); // works fine

    byte[] barray = {(byte)0x8f, (byte)0xd5, (byte)0xaf, (byte)0x30, (byte)0xb9};        

    String test1 = new String(barray); // breaks      
    testEqual(barray, test1);

    Charset cs = Charset.forName("UTF-8"); // breaks too
    String test2 = new String(barray, cs);       
    testEqual(barray, test2, cs);
}

Demo: http://ideone.com/IRHlb

PS: I don’t want to use Base64 or somesuch

Answer 1

You appear to be trying to store arbitrary binary data by converting it to a string using the platform default encoding. Don’t do that. Use base64 or hex to represent arbitrary binary data as text. There are lots of classes for base64 conversion; I like this public domain one.

If the data really is a binary-encoded form of some text, you should specify that encoding explicitly – but this is only appropriate if the original data was text. (Using the platform default encoding is almost always a bad idea.)

Binary data and text data are very different. Converting opaque binary data into a string arbitrarily is like expecting to be able to load an arbitrary file into an image editor and see something useful.