Java：有整数，需要在0x00格式的字节中

Question

I have an integer used to seed my for loop:

for(int i = 0; i < value; i++)

Within my for loop I am seeding a byte array with byte content values that increment +1. For instance new byte[]{0x00}; But the 0x00 needs to be 0x01 on the next iteration, how can I convert my value of integer i into a value of byte in the 0x00 format?

I tried things like Byte.valueOf(Integer.toHexString(i)) but this just gives me a value that looks like 0 instead of 0x00 .

Answer 1

new byte[]{0x00}

is actually equivalent to

new byte[]{0}

The 0x00 notation is just an alternative way to write integer constants, and if the integer constant is in the range -128 to 127, then it can be used as a byte.

If you have an existing integer variable that you want to use, and its value is in the range -128 to 127, then you just have to cast it:

int i = 1;
new byte[]{(byte)i};

Answer 2

I think the real problem is that you are confused about number representations and text renderings of numbers. Here are some key facts that you need to understand:

• The byte type is the set of integral values from -128 to +127.

• All integral types use the same representation (2's complement). The difference between the different types is their ranges.

• When you "see" a number, what you are seeing is a rendering of the number into a sequence of characters. There are MANY possible renderings; eg the number represented in memory as 00101010 (42) can be rendered as "42" or "+42" or "0x2a" or ... "forty two" .

• The default format for rendering a byte , short , int and long is the same; ie an optional minus sign followed by 1 or more decimal digits (with no zero padding). If you want to see your numbers formatted differently, then you need to do the formatting explicitly; eg using String.format(...) .

So to pull this together, if you want the bytes to look like 0x00 and 0x01 when you output or display them, you need to format them appropriately as you output / display them. In your example code, I doubt that there is anything wrong with the numbers themselves, or with the loop you are using to populate the array.

Answer 3

You are confusing the string representation of the value with the value itself. A value can be represented as binary, decimal, or hex, but it is still the same value.

If you want to use your integer to initialise a byte array, you just need to cast your integer value to a byte value as follows:

arr[i] = (byte) i;

Answer 4

I would just like to note that 0 is NOT the same thing as 0x00. If i were to use:

ColorChooserOutputText.append(Integer.toHexString(list[i].getRed()));                                           
ColorChooserOutputText.append(Integer.toHexString(list[i].getGreen()));                                      
ColorChooserOutputText.append(Integer.toHexString(list[i].getBlue()));

and wanted to return the color, Purple it would return: ff0cc Which would be fine if I were just using Java. But if you are going between Java and something that had format specific needs ff0cc would not produce purple.. ff00cc is actually purple.

    //Declare some variables.
    Color HexColor = JButton1.getBackground();

    String MyRValue = null;
    String MyGValue = null;
    String MyBValue = null;

    //Get Hex Value
    MyRValue = Integer.toHexString(HexColor.getRed());
    MyGValue = Integer.toHexString(HexColor.getGreen());
    MyBValue = Integer.toHexString(HexColor.getBlue());

    //Make sure to keep both 0's                    
    MyRValue = ("00"+MyRValue).substring(MyRValue.length());
    MyGValue = ("00"+MyGValue).substring(MyGValue.length());
    MyBValue = ("00"+MyBValue).substring(MyBValue.length());

    //Format your HexColor to #00ff00, #000000, #ff00ee
    JTextArea1.append("#");
    JTextArea1.append(MyRValue+MyGValue+MyBValue);
    JTextArea1.append(", ");

Answer 5

You want

new byte[]{(byte)i}

How you print this array is another matter. Look up printf in the API reference.

Answer 6

String.Format ("%02x") is your friend :)

http://download.oracle.com/javase/1.5.0/docs/api/java/util/Formatter.html

http://www.xinotes.org/notes/note/1195/