Unsigned short in Java_问答_开发者_运维开发者技术经验分享

How can I de开发者_如何学JAVAclare an unsigned short value in Java?

You can't, really. Java doesn't have any unsigned data types, except char.

Admittedly you could use char - it's a 16-bit unsigned type - but that would be horrible in my view, as char is clearly meant to be for text: when code uses char, I expect it to be using it for UTF-16 code units representing text that's interesting to the program, not arbitrary unsigned 16-bit integers with no relationship to text.

If you really need a value with exactly 16 bits:

Solution 1: Use the available signed short and stop worrying about the sign, unless you need to do comparison (<, <=, >, >=) or division (/, %, >>) operations. See this answer for how to handle signed numbers as if they were unsigned.

Solution 2 (where solution 1 doesn't apply): Use the lower 16 bits of int and remove the higher bits with & 0xffff where necessary.

This is a really stale thread, but for the benefit of anyone coming after. The char is a numeric type. It supports all of the mathematical operators, bit operations, etc. It is an unsigned 16.

We process signals recorded by custom embedded hardware so we handle a lot of unsigned 16 from the A-D's. We have been using chars all over the place for years and have never had any problems.

You can use a char, as it is an unsigned 16 bit value (though technically it is a unicode character so could potnetially change to be a 24 bit value in the future)... the other alternative is to use an int and make sure it is within range.

Don't use a char - use an int :-)

And here is a link discussing Java and the lack of unsigned.

From DataInputStream.java

public final int readUnsignedShort() throws IOException {
    int ch1 = in.read();
    int ch2 = in.read();
    if ((ch1 | ch2) < 0)
        throw new EOFException();
    return (ch1 << 8) + (ch2 << 0);
}

No such type in java

It is not possible to declare a type unsigned short, but in my case, I needed to get the unsigned number to use it in a for loop. There is the method toUnsignedInt in the class Short that returns "the argument converted to int by an unsigned conversion":

short signedValue = -4767;
System.out.println(signedValue ); // prints -4767

int unsignedValue = Short.toUnsignedInt(signedValue);
System.out.println(unsingedValue); // prints 60769

Similar methods exist for Integer and Long:

Integer.toUnsignedLong

Long.toUnsignedString : In this case it ends up in a String because there isn't a bigger numeric type.

Yep no such thing if you want to use the value in code vs. bit operations.

"In Java SE 8 and later, you can use the int data type to represent an unsigned 32-bit integer, which has a minimum value of 0 and a maximum value of 232-1." However this only applies to int and long but not short :(

If using a third party library is an option, there is jOOU (a spin off library from jOOQ), which offers wrapper types for unsigned integer numbers in Java. That's not exactly the same thing as having primitive type (and thus byte code) support for unsigned types, but perhaps it's still good enough for your use-case.

import static org.joou.Unsigned.*;

// and then...
UShort s = ushort(1);

(Disclaimer: I work for the company behind these libraries)

No, really there is no such method, java is a high-level language. That's why Java doesn't have any unsigned data types.

He said he wanted to create a multi-dimensional short array. Yet no one suggested bitwise operators? From what I read you want to use 16 bit integers over 32 bit integers to save memory?

So firstly to begin 10,000 x 10,000 short values is 1,600,000,000 bits, 200,000,000 bytes, 200,000 kilobytes, 200 megabytes.

If you need something with 200MB of memory consumption you may want to redesign this idea. I also do not believe that will even compile let alone run. You should never initialize large arrays like that if anything utilize 2 features called On Demand Loading and Data Caching. Essentially on demand loading refers to the idea to only load data as it is needed. Then data caching does the same thing, but utilizes a custom frame work for delete old memory and adding new information as needed. This one is tricky to have GOOD speed performance. There are other things you can do, but those two are my favorite when done right.

Alright back to what I was saying about bitwise operators.

So a 32bit integer or in Java "int". You can store what are called "bits" to this so let's say you had 32 Boolean values which in Java all values take up 32 bits (except long) or for arrays they take up 8 for byte, 16 for short, and 32 for int. So unless you have arrays you don't get any memory benefits from using a byte or short. This does not mean you shouldn't use it as its a way to ensure you and others know the data range this value should have.

Now as I was saying you could effectively store 32 Booleans into a single integer by doing the following:

int many_booleans = -1; //All are true;
int many_booleans = 0; //All are false;
int many_booleans = 1 | 2 | 8; //Bits 1, 2, and 4 are true the rest are false;

So now a short consists of 16 bits so 16 + 16 = 32 which fits PERFECTLY within a 32bit integer. So every int value can consist of 2 short values.

int two_shorts = value | (value2 << 16);

So what the above is doing is value is something between -32768 and 32767 or as an unsigned value 0 - 65535. So let's say value equaled -1 so as an unsigned value it was 65535. This would mean bits 1 through 16 are turned on, but when actually performing the math consider the range 0 - 15.

So we need to then activate bits 17 - 32. So we must begin at something larger than 15 bits. So we begin at 16 bits. So by taking value2 and multiplying it by 65536 which is what "<< 16" does. We now would have let's say value2 equaled 3 it would be OR'd 3x65536 = 196608. So our integer value would equal 262143.

int assumed_value = 262143;

so let's say we want to retrieve the two 16bit integer values.

short value1 = (short)(assumed_value & 0xFFFF); //-1
short value2 = (short)(assumed_value >> 16); //=3

Also basically think of bitwise operators as powers of 2. That is all they really are. Never look at it terms of 0's and 1's. I mostly posted this to assist anyone who may come across this searching for unsigned short or even possibly multi-dimensional arrays. If there are any typo's I apologize quickly wrote this up.

Java does not have unsigned types. What do you need it for?

Java does have the 'byte' data type, however.

You can code yourself up a ShortUnsigned class and define methods for those operators you want. You won't be able to overload + and - and the others on them, nor have implicit type conversion with other primitive or numeric object types, alas.

Like some of the other answerers, I wonder why you have this pressing need for unsigned short that no other data type will fill.

Simple program to show why unsigned numbers are needed:

package shifttest;
public class ShiftTest{
    public static void main(String[] args){
        short test = -15000;
        System.out.format ("0x%04X 0x%04X 0x%04X 0x%04X 0x%04X\n",
            test, test>>1, test>>2, test>>3, test>>4);
    }
}

results:

0xC568 0xFFFFE2B4 0xFFFFF15A 0xFFFFF8AD 0xFFFFFC56

Now for those that are not system types:

JAVA does an arithmetic shift because the operand is signed, however, there are cases where a logical shift would be appropriate but JAVA (Sun in particular), deemed it unnecessary, too bad for us on their short sightedness. Shift, And, Or, and Exclusive Or are limited tools when all you have are signed longer numbers. This is a particular problem when interfacing to hardware devices that talk "REAL" computer bits that are 16 bits or more. "char" is not guaranteed to work (it is two bytes wide now) but in several eastern gif based languages such as Chinese, Korean, and Japanese, require at least 3 bytes. I am not acquainted with the number need for sandscript style languages. The number of bytes does not depend on the programmer rather the standards committee for JAVA. So basing char as 16 bits has a downstream risk. To safely implement unsigned shorts JAVA, as special class is the best solution based on the aforementioned ambiguities. The downside of the class is the inability of overloading the mathematical operations for this special class. Many of the contributors for this thread of accurately pointed out these issues but my contribution is a working code example and my experience with 3 byte gifs languages in C++ under Linux.

//вот метод для получения аналога unsigned short
    public static int getShortU(byte [] arr, int i )  throws Exception 
    {
       try
       {
           byte [] b = new byte[2]; 
           b[1] = arr[i];
           b[0] = arr[i+1];
           int k = ByteBuffer.wrap(b).getShort();
            //if this: 
           //int k = ((int)b[0] << 8) + ((int)b[1] << 0); 
           //65536 = 2**16
           if ( k <0) k = 65536+ k; 
        return k;
      }  
       catch(Throwable t)
      {
          throw  new Exception ("from getShort: i=" + i);
      }
    }