Java：“[B@1ef9157”背后的语法和含义？二进制/地址？

发布于 2024-07-26 04:45:33 字数 697 浏览 2 评论 0原文

嘿，我正在尝试弄清楚 [B@ 前缀在 java 中的含义。当我尝试打印字节数组时，它们就会出现。但是，大小为 32 和大小为 4 的字节数组的长度相同。始终“[@B1234567”。

这是什么？此外，它们还具有仅打印十六进制值的属性。我知道它不能只是二进制打印，因为会出现随机扩展的 ascii 字符。

下面是 byte[] 到 byte[] 哈希表映射打印的示例，其中映射由冒号分隔，这些是 4 字节键和 32 字节元素的字节数组。

[B@1ef9157:[B@1f82982
[B@181ed9e:[B@16d2633
[B@27e353:[B@e70e30
[B@cb6009:[B@154864a
[B@18aaa1e:[B@3c9217
[B@20be79:[B@9b42e6
[B@16925b0:[B@14520eb
[B@8ee016:[B@1742700
[B@1bfc93a:[B@acb158
[B@107ebe1:[B@1af33d6
[B@156b6b9:[B@17431b9
[B@139b78e:[B@16c79d7
[B@2e7820:[B@b33d0a
[B@82701e:[B@16c9867
[B@1f14ceb:[B@89cc5e
[B@da4b71:[B@c837cd
[B@ab853b:[B@c79809
[B@765a16:[B@1ce784b
[B@1319c:[B@3bc473

原文

Hey, I'm trying to figure out what the [B@ prefix means in java. They come out when I attempt to print byte arrays. However, byte arrays of size 32 and size 4 are identical in length. Always "[@B1234567".

What is this? Also, they have the property of only printing hex values. I know it can't just be a binary print because random extended ascii chars would appear.

Here is an example of a byte[] to byte[] hashtable mapping print, where mappings are separated by a colon, and these are byte arrays of 4-byte keys and 32-byte elements.

[B@1ef9157:[B@1f82982
[B@181ed9e:[B@16d2633
[B@27e353:[B@e70e30
[B@cb6009:[B@154864a
[B@18aaa1e:[B@3c9217
[B@20be79:[B@9b42e6
[B@16925b0:[B@14520eb
[B@8ee016:[B@1742700
[B@1bfc93a:[B@acb158
[B@107ebe1:[B@1af33d6
[B@156b6b9:[B@17431b9
[B@139b78e:[B@16c79d7
[B@2e7820:[B@b33d0a
[B@82701e:[B@16c9867
[B@1f14ceb:[B@89cc5e
[B@da4b71:[B@c837cd
[B@ab853b:[B@c79809
[B@765a16:[B@1ce784b
[B@1319c:[B@3bc473

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晨曦÷微暖 2024-08-02 04:45:34

您正在查看对象 ID，而不是内容转储。

[ 表示数组。
B 表示字节。
@ 将类型与 ID 分开。
十六进制数字是对象 ID 或哈希码。

如果目的是打印数组的内容，有很多方法。例如：

byte[] in = new byte[] { 1, 2, 3, -1, -2, -3 };
System.out.println(byteArrayToString(in));

String byteArrayToString(byte[] in) {
    char out[] = new char[in.length * 2];
    for (int i = 0; i < in.length; i++) {
        out[i * 2] = "0123456789ABCDEF".charAt((in[i] >> 4) & 15);
        out[i * 2 + 1] = "0123456789ABCDEF".charAt(in[i] & 15);
    }
    return new String(out);
}

完整列表类型命名法可以在 JNI 文档。

以下是完整列表：

B - 字节
C - 字符
D - 双精度
F - 浮点
I - int
J - long
L***完全限定类*;** - 介于 L 和 < code>; 是完整的类名，使用 / 作为包之间的分隔符（例如，Ljava/lang/String;）
S< /strong> - 短
Z - 布尔值
[ - 数组的每个维度都有一个 [
(***参数类型*< /strong>)***return-type* - 方法签名，例如 (I)V，带有用于 void 方法的附加伪类型 V

You're looking at the object ID, not a dump of the contents.

The [ means array.
The B means byte.
The @ separates the type from the ID.
The hex digits are an object ID or hashcode.

If the intent is to print the contents of the array, there are many ways. For example:

byte[] in = new byte[] { 1, 2, 3, -1, -2, -3 };
System.out.println(byteArrayToString(in));

String byteArrayToString(byte[] in) {
    char out[] = new char[in.length * 2];
    for (int i = 0; i < in.length; i++) {
        out[i * 2] = "0123456789ABCDEF".charAt((in[i] >> 4) & 15);
        out[i * 2 + 1] = "0123456789ABCDEF".charAt(in[i] & 15);
    }
    return new String(out);
}

A complete list of the type nomenclature can be found in the JNI documentation.

Here is the entire list:

B - byte
C - char
D - double
F - float
I - int
J - long
L***fully-qualified-class*;** - between an L and a ; is the full class name, using / as the delimiter between packages (for example, Ljava/lang/String;)
S - short
Z - boolean
[ - one [ for every dimension of the array
(***argument types*)***return-type* - method signature, such as (I)V, with the additional pseudo-type of V for void method

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真心难拥有 2024-08-02 04:45:34

[B@ 表示“字节数组”。其他基本数组类型具有不同的前缀：

class Test
{   
    public static void main(String [] args)
    {
        byte[] b = new byte[0];
        int[] i = new int[0];
        char[] c = new char[0];
        long[] l = new long[0];
        double[] d = new double[0];
        float[] f = new float[0];
        short[] s = new short[0];        

        System.out.println(b);
        System.out.println(i);
        System.out.println(c.toString());
        System.out.println(l);
        System.out.println(d);
        System.out.println(f);
        System.out.println(s);
    }
}

打印：

[B@3e25a5
[I@19821f
[C@addbf1
[J@42e816
[D@9304b1
[F@190d11
[S@a90653

非基本类型包括 [L 之后的类型名称，例如：

[Ljava.lang.String;@a90653
[Ljava.lang.Object;@de6ced

如果您想将字节数组的内容打印为十六进制，这里有一些代码可以帮助您你：

class Test
{   
    public static void main(String [] args)
    {
        byte[] b = new byte[] { (byte) 0xf3, (byte) 0xf1, (byte) 0x7f };
        System.out.println(toHex(b));
    }

    private static final char[] HEX_DIGITS = "0123456789abcdef".toCharArray();
    public static String toHex(byte[] bytes)
    {
        char[] c = new char[bytes.length*2];
        int index = 0;
        for (byte b : bytes)
        {
            c[index++] = HEX_DIGITS[(b >> 4) & 0xf];
            c[index++] = HEX_DIGITS[b & 0xf];
        }
        return new String(c);
    }
}

[B@ means "byte array". Other primitive array types have different prefixes:

class Test
{   
    public static void main(String [] args)
    {
        byte[] b = new byte[0];
        int[] i = new int[0];
        char[] c = new char[0];
        long[] l = new long[0];
        double[] d = new double[0];
        float[] f = new float[0];
        short[] s = new short[0];        

        System.out.println(b);
        System.out.println(i);
        System.out.println(c.toString());
        System.out.println(l);
        System.out.println(d);
        System.out.println(f);
        System.out.println(s);
    }
}

Prints:

[B@3e25a5
[I@19821f
[C@addbf1
[J@42e816
[D@9304b1
[F@190d11
[S@a90653

Non-primitive types include the type name after [L for instance:

[Ljava.lang.String;@a90653
[Ljava.lang.Object;@de6ced

If you want to print the contents of a byte array as hex, here's some code to help you:

class Test
{   
    public static void main(String [] args)
    {
        byte[] b = new byte[] { (byte) 0xf3, (byte) 0xf1, (byte) 0x7f };
        System.out.println(toHex(b));
    }

    private static final char[] HEX_DIGITS = "0123456789abcdef".toCharArray();
    public static String toHex(byte[] bytes)
    {
        char[] c = new char[bytes.length*2];
        int index = 0;
        for (byte b : bytes)
        {
            c[index++] = HEX_DIGITS[(b >> 4) & 0xf];
            c[index++] = HEX_DIGITS[b & 0xf];
        }
        return new String(c);
    }
}

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