Скачать или смотреть Understanding Kotlin Conversion to and from Byte Array

A beginner's guide on converting doubles to byte arrays in Kotlin, including tips on handling negative numbers for accurate data conversion.
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Mastering Byte Array Conversion in Kotlin

When working with data in Kotlin, it often becomes necessary to convert objects into byte arrays for various applications, such as saving data or network communication. One common issue arises when handling primitive types, especially with doubles. This guide will delve deeper into the problem of converting a double to an 8-byte format and ensuring that conversions from byte arrays preserve the integrity of the data.

The Problem

Imagine you've created a class with several variables of primitive types, and you're trying to convert a double value to an 8-byte array. Upon retrieving the value, you find that it isn't the same as the original—it's close, but not exact. This kind of discrepancy often stems from issues related to handling negative values within the byte array conversion process.

The Solution

To fix the issue, it's important to understand how negative numbers are represented in byte arrays and how to correctly shift and convert these values back and forth. Below, we'll break down both the writing and reading processes that you'll need to implement.

Writing to Byte Array

Here's the function you started with for writing a long integer to a byte array:

[[See Video to Reveal this Text or Code Snippet]]

Initialization: We create a byte array of size Long.SIZE_BYTES (8 bytes) and initialize our index and shift values.

Looping through Bytes: We shift the long integer right by 8 * size and apply a mask with 0xFFL to capture only the last byte.

Storing Bytes: Each processed byte is stored at the appropriate index in the byte array, ensuring accurate retrieval later.

Reading from Byte Array

Here's the original reading function you implemented:

[[See Video to Reveal this Text or Code Snippet]]

This function has a fundamental flaw when dealing with negative byte values.

Negative Numbers Issue: When bytes are negative, they are represented by a 0xFF value. For instance, when a byte containing FF (or -1 in decimal) is converted, it does not translate as expected. The line:

[[See Video to Reveal this Text or Code Snippet]]

treats the byte incorrectly. The conversion can yield unexpected results, such as 0xFFFFFFFFFFFFFFFF, instead of 0x00000000000000FF.

Correcting the Read Method

To ensure accurate conversion, modify the line to mask the byte properly, like this:

[[See Video to Reveal this Text or Code Snippet]]

Summary

To summarize, when converting from a byte array to a long in Kotlin:

Always mask the byte with 0xFF to capture only the lowest byte.

Understand the behavior of positive and negative numbers during conversion to ensure you are manipulating the correct values.

Conclusion

By implementing these changes, you can confidently convert a double to a byte array in Kotlin and back without data loss or discrepancies. Remember, handling byte representation can seem tricky at first, but with practice, you'll master the art of data conversion. Happy coding!