JVM大端判断

最新推荐文章于 2023-05-24 15:32:27 发布

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最新推荐文章于 2023-05-24 15:32:27 发布

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文章标签： java 操作系统

原文链接：http://www.cnblogs.com/z-sm/p/6049172.html

博客介绍了JVM采用大端方式存储多字节数据，阐述了大小端模式在存放字节顺序上的区别，大端将高位存低地址，与阅读顺序一致；小端将高位存高地址，利于计算机处理，且目前大小端优劣尚无定论。

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 interfaces java.io.DataInput and java.io.DataOutput and classes such as java.io.DataInputStream and java.io.DataOutputStream.

转载于:https://www.cnblogs.com/z-sm/p/6049172.html