Kotlin i.inc（）比i ++慢10倍？
所以今天我了解了kotlin中的num.inc（）特性，并决定在我的代码中实现它。 不用说，这增加了我的代码的延迟时间的10倍（从〜400ms到4000 + ms）
这是我的传统方式（i ++，400ms）
package com.beaudoin import java.io.BufferedWriter import java.io.FileInputStream import java.io.FileWriter import java.nio.channels.FileChannel fun main(args: Array<String>) { val s = System.currentTimeMillis() val channel = FileInputStream("client.dll").channel val buffer = channel.map(FileChannel.MapMode.READ_ONLY, 0, channel.size()) val data = ByteArray(buffer.capacity()) buffer.get(data) val writer = BufferedWriter(FileWriter("dump.txt", false)) val bytes = ByteArray(16) var offset = 0 var i = 0 while (i < data.size) { for (j in bytes.indices) { bytes[j] = data[i++] } writer.write(HexRow(offset, bytes).toString()) writer.newLine() offset += 16 } writer.close() println(System.currentTimeMillis() - s) } private val HEX_ARRAY = "0123456789ABCDEF".toCharArray() private val bytes = ByteArray(4); class HexRow(val offset: Int, val values: ByteArray) { fun bytesToChar(bytes: ByteArray, width: Int): CharArray { val hexChars = CharArray((bytes.size * 2) + (bytes.size / width)) for (i in bytes.indices) { val v = bytes[i].toInt() and 0xFF val idx = (i * 2) + i / width hexChars[idx] = HEX_ARRAY[v.ushr(4)] hexChars[idx + 1] = HEX_ARRAY[v and 0x0F] if (idx + 2 < hexChars.size) { hexChars[idx + 2] = ' ' } } return hexChars; } fun bytesToHex(value: Int) = String(bytesToChar(toByteArray(value), 6)) fun bytesToHex(bytes: ByteArray) = String(bytesToChar(bytes, 1)) fun toByteArray(value: Int): ByteArray { bytes[0] = value.ushr(24).toByte() bytes[1] = value.ushr(16).toByte() bytes[2] = value.ushr(8).toByte() bytes[3] = value.toByte() return bytes } override fun toString() = bytesToHex(offset) + " " + bytesToHex(values) } 这里是使用i.inc（）（4000ms +）的代码
package com.beaudoin import java.io.BufferedWriter import java.io.FileInputStream import java.io.FileWriter import java.nio.channels.FileChannel fun main(args: Array<String>) { val s = System.currentTimeMillis() val channel = FileInputStream("client.dll").channel val buffer = channel.map(FileChannel.MapMode.READ_ONLY, 0, channel.size()) val data = ByteArray(buffer.capacity()) buffer.get(data) val writer = BufferedWriter(FileWriter("dump.txt", false)) val bytes = ByteArray(16) var offset = 0 /* var i = 0 while (i < data.size) { for (j in bytes.indices) { bytes[j] = data[i++] } writer.write(HexRow(offset, bytes).toString()) writer.newLine() offset += 16 }*/ for (i in data.indices) { for (j in bytes.indices) { bytes[j] = data[i] i.inc() } writer.write(HexRow(offset, bytes).toString()) writer.newLine() offset += 16 } writer.close() println(System.currentTimeMillis() - s) } private val HEX_ARRAY = "0123456789ABCDEF".toCharArray() private val bytes = ByteArray(4); class HexRow(val offset: Int, val values: ByteArray) { fun bytesToChar(bytes: ByteArray, width: Int): CharArray { val hexChars = CharArray((bytes.size * 2) + (bytes.size / width)) for (i in bytes.indices) { val v = bytes[i].toInt() and 0xFF val idx = (i * 2) + i / width hexChars[idx] = HEX_ARRAY[v.ushr(4)] hexChars[idx + 1] = HEX_ARRAY[v and 0x0F] if (idx + 2 < hexChars.size) { hexChars[idx + 2] = ' ' } } return hexChars; } fun bytesToHex(value: Int) = String(bytesToChar(toByteArray(value), 6)) fun bytesToHex(bytes: ByteArray) = String(bytesToChar(bytes, 1)) fun toByteArray(value: Int): ByteArray { bytes[0] = value.ushr(24).toByte() bytes[1] = value.ushr(16).toByte() bytes[2] = value.ushr(8).toByte() bytes[3] = value.toByte() return bytes } override fun toString() = bytesToHex(offset) + " " + bytesToHex(values) }
有人可以告诉我为什么i.inc（）比i ++慢得多吗？
PS：用任何文件替换client.dll（应该是〜12mb，以获得准确的数字我的或简单地下载我的测试文件在这里
inc()在你的代码中调用是完全多余的：它不会改变变量：
var x = 0 x.inc() println(x) // 0
对于运行时间的差异，两种实现的语义也是不同的：
-
第一个片段：
while (i < data.size) { for (j in bytes.indices) { bytes[j] = data[i++] } //... }内循环改变
i，所以不会有迭代，while对于每一个i，i一些（甚至大部分，我想）值将被跳过。 -
第二个片段：
for (i in data.indices) { for (j in bytes.indices) { bytes[j] = data[i] // removed redundant i.inc() } //... }内循环在外循环中被调用，因此需要更长的时间。