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Thread: Java equivalent of Python’s struct.pack?

  1. #1
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    Default Java equivalent of Python’s struct.pack?

    Is there any function equivalent to Python's struct.pack in Java that allows me to pack and unpack values like this?

    pump_on = struct.pack("IIHHI", 0, 0, 21, 96, 512)
    event = open(("/dev/input/event7"), "r+",0)
    event.write(valve_on)


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    Default Re: Java equivalent of Python’s struct.pack?

    Not as far as I know, but you can serialize Java objects that implement the Serializable interface and then use the Object writer to write the object data to a binary file.

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    Super Moderator Json's Avatar
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    Default Re: Java equivalent of Python’s struct.pack?

    I take it you're actually creating a struct of a files contents there, in theory you could do this with a byte array.

    This might not be what you want and there might be a more simple solution to this but at least it works

        public static void main(String[] args) throws Throwable {
            // Create a "struct" or a buffer that we wish to output
            final ByteBuffer outputByteBuffer = ByteBuffer.allocate(30);
            outputByteBuffer.putChar('I').putChar('I').putChar('H').putChar('H').putChar('I').putInt(0).putInt(0).putInt(21).putInt(96).putInt(512);
            outputByteBuffer.flip();
     
            // Write the buffer to a file
            final File file = new File("/dev/input/event7");
            final FileOutputStream fileOutputStream = new FileOutputStream(file);
            fileOutputStream.getChannel().write(outputByteBuffer);
            fileOutputStream.close();
     
            // Open the file and read in the buffer
            final ByteBuffer inputByteBuffer = ByteBuffer.allocate(30);
            final FileInputStream fileInputStream = new FileInputStream(file);
            fileInputStream.getChannel().read(inputByteBuffer);
            fileInputStream.close();
     
            // Each character takes 2 bytes so therefore we have the characters at index 0, 2, 4, 6 and 8
            System.out.println(Character.toString(inputByteBuffer.getChar(0)) + Character.toString(inputByteBuffer.getChar(2)) + Character.toString(inputByteBuffer.getChar(4)) + Character.toString(inputByteBuffer.getChar(6)) + Character.toString(inputByteBuffer.getChar(8)));
     
            // First int will be on index 10 because of the 2 bytes taken by the character before it
            System.out.println(inputByteBuffer.getInt(10));
     
            // Second int will be a at 14 because an int takes 4 bytes
            System.out.println(inputByteBuffer.getInt(14));
     
            // Third int will be a at 14 because an int takes 4 bytes
            System.out.println(inputByteBuffer.getInt(18));
     
            // Forth int will be a at 14 because an int takes 4 bytes
            System.out.println(inputByteBuffer.getInt(22));
     
            // Fifth int will be a at 14 because an int takes 4 bytes
            System.out.println(inputByteBuffer.getInt(26));
     
        }

    // Json

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