Android studio - byte operations - changing value

Question

I have a problem with bit operations

int progress = slider.getProgress(); value of user input

then I have to do shift left and change it to HEX

int shl = 1<<progress-1;
String hexStr = Integer.toHexString(shl);

Nex Im sending bytes by BT

byte bit = Byte.decode(hexStr)
command[2]=bit;

Now the problem If user set for example 2 it is ok 0b100 = 0x04

But if user set 5 0b10000 = hexStr = 10 in command[2] it gets value 0x0A

Why is it changing value?

It's been a while since I worked with bit shifting, but are you sure you are actually experiencing an error? If I still remember how to do this, then 5 is 0101 in binary, which becomes 1010 when bit-shifted left. 10 represented in Hex is A, which is the value you are getting. — Lasse Samson, Jun 14 '17 at 12:27
I need only one "1" in whole command to send by BT If user set 5 it means 5th led should light so 10000 If user set 10 - 10th led should light 1000000000 Im not translating decimal to bin or hex, but the user input tells on which position "1" should go Hope its clear :) — Max Kolanko, Jun 14 '17 at 12:53

VC.One · Answer 1 · 2017-06-17T17:18:38.247

"But if user set 5 0b10000 = hexStr = 10 in command[2] it gets value = 0x0A.
Why is it changing value?"

It is correct. What different result are you expecting?

For example : If progress is 5 then...

Doing bit shift like 1 << progress-1 == 1 << 4 = (resulting bits= 0001 0000) which gives :
int shl = 10 in hex format or even int shl = 16 in decimal format
Doing String hexStr = Integer.toHexString(shl); puts shl's "10" hex string value to the other string hexStr (ie: is also now a "10")...
Doing byte bit = Byte.decode(hexStr) makes a byte with a decimal value of hexStr's "10".

This is how your result is command[2] saying hex value of 0x0A which == decimal value of 10.

....

"I'm not translating decimal to binary or hex, but the user input which tells on which position "1" should go. Hope it's clear..."

Why not just write "1" and then add as many zeroes as required (padding)?

Note: I'm not sure what value command[2]= is supposed to get. Maybe it checks the 8 bits of that byte, or maybe it expects a number (integer). It's confusng becuase your numbers rely on "1 followed by zeroes", also binary can be "1 followed by zeroes"

Binary : There are 8 bits in a byte, so the max binary you can send is 10000000 only.
Integer : A single byte is signed so the max value s 128. By this logic your options are 1, 10, 100 only.

See if this helps (check which command[2]= you want. I've commented // them out for now) :

    int progress = 5; 
    int shl = 1 << progress-1; //why??

    String hexStr = Integer.toHexString(shl);
    String shlStr = Integer.toString(shl);

    String zeroStr = "";

    byte bit = Byte.decode(hexStr);
    //command[2]=bit;

    System.out.println("shl result string  : "  + shlStr);
    System.out.println("Bytes string hex : "  + hexStr);

    //# Padding
    for(int i = 0; i < (progress-1); i++) 
    { zeroStr += "0"; }    

    shlStr = "1" + zeroStr;
    //command[2]= Byte.decode(shlStr);

    System.out.println("Result string hex : "  + zeroStr);
    System.out.println("shi padding string  : "  + shiStr);

Android studio - byte operations - changing value

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