JVM大端判断
JVM采用大端方式存多字节的数据,判断方法如下:
1 public static void bytesToInt() throws IOException { 2 /** 3 * 将字节数组(byte[])转为整形(int) 4 */ 5 byte[] byteAr = new byte[] { 0x78, 0x56, 0x34, 0x12 }; 6 ByteArrayInputStream bais = new ByteArrayInputStream(byteAr); 7 DataInputStream dis = new DataInputStream(bais); 8 System.out.println(Integer.toHexString(dis.readInt()));// output: 78563412,说明是大端 9 } 10 11 public static void intToBytes() throws IOException { 12 /** 13 * 将整形(int)转为字节数组(byte[]) 14 */ 15 int a = 0x12345678; 16 ByteArrayOutputStream baos = new ByteArrayOutputStream(); 17 DataOutputStream dos = new DataOutputStream(baos); 18 dos.writeInt(a); 19 byte[] b = baos.toByteArray(); 20 for (int i = 0; i < 4; i++) { 21 System.out.print(Integer.toHexString(b[i])); 22 } 23 System.out.println();// Output: 12345678,说明是大端 24 }
采用大小模式对数据进行存放的主要区别在于在存放的字节顺序,大端方式将高位存放在低地址,小端方式将高位存放在高地址。采用大端方式数据存放与阅读顺序一致,符合人类的正常思维,而采用小端方式进行数据存放利于计算机处理。到目前为止,采用大端或者小端进行数据存放,其孰优孰劣也没有定论。
参考资料:
Java's Virtual Machine's Endianness-StackOverFlow
The Java Virtual Machine Specification, Java SE 7 Edition, Chapter 4: The class File Format
A
class
file consists of a stream of 8-bit bytes. All 16-bit, 32-bit, and 64-bit quantities are constructed by reading in two, four, and eight consecutive 8-bit bytes, respectively. Multibyte data items are always stored in big-endian order, where the high bytes come first. In the Java SE platform, this format is supported by interfacesjava.io.DataInput
andjava.io.DataOutput
and classes such asjava.io.DataInputStream
andjava.io.DataOutputStream
.