Java：将字节转换为整数

Question

I need to convert 2 byte array ( byte[2] ) to integer value in java. How can I do that?

Answer 1

You can use ByteBuffer for this:

ByteBuffer buffer = ByteBuffer.wrap(myArray);
buffer.order(ByteOrder.LITTLE_ENDIAN);  // if you want little-endian
int result = buffer.getShort();

See also Convert 4 bytes to int .

Answer 2

In Java, Bytes are signed, which means a byte's value can be negative, and when that happens, @MattBall's original solution won't work.

For example, if the binary form of the bytes array are like this:

1000 1101 1000 1101

then myArray[0] is 1000 1101 and myArray[1] is 1000 1101 , the decimal value of byte 1000 1101 is -115 instead of 141(= 2^7 + 2^3 + 2^2 + 2^0)

if we use

int result = (myArray[0] << 8) + myArray[1]

the value would be -16191 which is WRONG.

The reason why its wrong is that when we interpret a 2-byte array into integer, all the bytes are unsigned, so when translating, we should map the signed bytes to unsigned integer:

((myArray[0] & 0xff) << 8) + (myArray[1] & 0xff)

the result is 36237 , use a calculator or ByteBuffer to check if its correct(I have done it, and yes, it's correct).

Answer 3

Also, if you can use the Guava library:

Ints.fromByteArray(0, 0, myArray[1], myArray[0]);

It was worth mentioning since a lot of projects use it anyway.

Answer 4

Simply do this:

return new BigInteger(byte[] yourByteArray).intValue();

Works great on Bluetooth command conversions etc. No need to worry about signed vs. unsigned conversion.

Answer 5

Well, each byte is an integer in the range -128..127, so you need a way to map a pair of integers to a single integer. There are many ways of doing that, depending on what you have encoded in the pair of bytes. The most common will be storing a 16-bit signed integer as a pair of bytes. Converting that back to an integer depends on whether you store it big-endian form:

(byte_array[0]<<8) + (byte_array[1] & 0xff)

or little endian:

(byte_array[1]<<8) + (byte_array[0] & 0xff)