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：

    public static void bytesToInt() throws IOException {
        /**
         * 将字节数组（byte[]）转为整形(int)
         */
        byte[] byteAr = new byte[] { 0x78, 0x56, 0x34, 0x12 };
        ByteArrayInputStream bais = new ByteArrayInputStream(byteAr);
        DataInputStream dis = new DataInputStream(bais);
        System.out.println(Integer.toHexString(dis.readInt()));// output: 78563412，说明是大端
    }

    public static void intToBytes() throws IOException {
        /**
         * 将整形(int)转为字节数组（byte[]）
         */
        int a = 0x12345678;
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        DataOutputStream dos = new DataOutputStream(baos);
        dos.writeInt(a);
        byte[] b = baos.toByteArray();
        for (int i = 0; i < 4; i++) {
            System.out.print(Integer.toHexString(b[i]));
        }
        System.out.println();// Output: 12345678，说明是大端
    }

 

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.