How to pick out part of bits from a 8bytes data in java

Question

I am new to Java. I have 8 bytes (or dlc bytes ) of data in Java, which looks like this :

int dlc = 8;
byte[] myData = new byte[dlc];

Then I would like to get the value (start bit is 50, length is 2 bits) from myData.

My idea is to convert myData to bits, then find the value start from bits 50 and has a length of 2 bits, then convert the bits values to integer, is this method good ? if it's available, then how to do it in java ? if it's not, any ideas to pick out some part of value from bytes array ?

Solution : The solution is provided by @Zoyd

NOTE : BitSet.valueOf(Bytebuffer) is added from Android API 19! so if you have earlier API level, you cannot use valueOf() method. You can look at BitSet to and from integer/long

You should look up bitwise operations. – Robadob Apr 25 '14 at 08:43 — Robadob, Apr 25 '14 at 08:43

score 1 · Answer 1 · answered Apr 25 '14 at 08:45

1

try this

(myData[6] & 0x60) >> 5

answered Apr 25 '14 at 08:45

Xing Fei

287
1
6

score 1 · Accepted Answer · answered Apr 25 '14 at 08:50

1

Xing Fei's anwer is fine, but if you need a general method, you can make a BitSet from your byte array :

final BitSet bs = BitSet.valueOf(myData);

Then, you can write, for example :

boolean b = bs.get(50);

to obtain the value of bit 50.

answered Apr 25 '14 at 08:50

Zoyd

3,449
1
18
27

This is only getting one bit value, how to get e.g. 9 bits of value and represent it into a integer ? – Heidi Apr 25 '14 at 09:19
bs.get(50,58) (returns another bitset) – Zoyd Apr 25 '14 at 09:21

score 0 · Answer 3 · answered Apr 25 '14 at 08:59

0

In explanation of Xing Fei: myData[6] gives you bits 49 to 56, by AND-ing this with 0x60 (= 01100000) you set bits 49, 52, 53, 54, 55, and 56 to zero. If you shift this 5 bits to the right (>> - Operator) you have your result.

answered Apr 25 '14 at 08:59

Jan

2,060
2
29
34

How to pick out part of bits from a 8bytes data in java

3 Answers3