使用Integer存储版本号

格式为 

1. (仿 java) 魔法数 1A2B占2个字节

2. 主版本号占1个字节(0~255)

3. 次版本号占1个字节(0~255)

可供升级的版本为 6W多个,基本够用了

/**
     * 1. 魔法数 1A2B占2个字节
     * 2. 主版本号占1个字节(0~255)
     * 3. 次版本号占1个字节(0~255)
     */
    static class Header implements Comparable<Header> {
        //魔法数
        private final static short MagicValue = 0x1A2B;
        //魔法数
        private short magicValue;
        //主版本号
        private byte mainVersion;
        //次版本号
        private byte subVersion;

        public Header(byte mainVersion, byte subVersion) {
            magicValue = MagicValue;
            this.mainVersion = mainVersion;
            this.subVersion = subVersion;
        }

        public int toInt() {
            //魔法值 右移16位,即占Int32的高16位
            //主版本号 右移8位,即点Int32的低16位中的高8位
            // 次版本号占低8位
            return (magicValue & 0xFFFF) << 16 |
                    (mainVersion & 0xFF) << 8 |
                    (subVersion & 0xFF);
        }

        public static int toInt(Header header) {
            return header.toInt();
        }

        public static Header toHeader(int headerInt) {
            // 首次校验header里的魔法位是不是正确的
            int mv = (headerInt >> 16) & 0xFFFF;
            if (mv != MagicValue) {
                throw new RuntimeException("格式不对");
            }
            byte mainVersion = (byte) ((headerInt >> 8) & 0xFF);
            byte subVersion = (byte) ((headerInt) & 0xFF);
            return new Header(mainVersion, subVersion);
        }

        public static int toInt(int mainVersion, int subVersion) {
            return (MagicValue & 0xFFFF) << 16 |
                    (mainVersion & 0xFF) << 8 |
                    (subVersion & 0xFF);
        }

        @Override
        public int compareTo(Header o) {
            if (o == null) {
                return 0;
            }
            return this.toInt() - o.toInt();
        }

        @Override
        public String toString() {
            return "Header{" +
                    //"magicValue=" + magicValue + "(" + String.format("%x", magicValue) + ")" +
                    "magicValue=" + magicValue + "(" + Integer.toHexString(magicValue) + ")" +
                    ", mainVersion=" + mainVersion +
                    ", subVersion=" + subVersion +
                    '}';
        }

        @Override
        public boolean equals(Object o) {
            if (this == o) {
                return true;
            }
            if (o == null || getClass() != o.getClass()) {
                return false;
            }

            Header header = (Header) o;
            return toInt() == header.toInt();
        }

        @Override
        public int hashCode() {
            return  toInt();
        }
    }

    public static Header makeHeader(byte mainVersion, byte subVersion) {
        return new Header(mainVersion, subVersion);
    }

    public static void main(String[] args) {

        Header header = makeHeader((byte) 1, (byte) 1);
        System.out.println(header);
        int headerInt = header.toInt();
        System.out.println(headerInt);
        Header header2 = Header.toHeader(headerInt);
        System.out.println(header2);
        Header header_1_20 = makeHeader((byte) 2, (byte) 20);
        System.out.println(header_1_20);
        System.out.println(header.compareTo(header_1_20));
        System.out.println(Header.toHeader(539025921));
    }

输出为:

Header{magicValue=6699(1a2b), mainVersion=1, subVersion=1}
439025921
Header{magicValue=6699(1a2b), mainVersion=1, subVersion=1}
Header{magicValue=6699(1a2b), mainVersion=2, subVersion=20}
-275

Exception in thread "main"

java.lang.RuntimeException: 格式不对

    at com.g2.IntToByteArray$Header.toHeader(IpV4Utils.java:135)
    at com.g2.IntToByteArray.main(IpV4Utils.java:200)

Process finished with exit code 1