unsigned : Java Glossary

byte b;
// ...
int i = b & 0xff;

To get the effect of a 16-bit unsigned use char.

To get the effect of a 32-bit unsigned:

int i;
// ...
long l = i & 0xffffffffL;

Here

// combining two unsigned shorts into an unsigned int.
short ush = 4;
short usl = 9999;
int ucombined = ( ush & 0xffff ) << 16 | ( usl & 0xffff );

For 64-bit unsigned, consider that addition and subtraction give you the same results whether you consider the operands signed or unsigned. When you multiply two unsigned 64-bit operands together you get a 128-bit result which won’t fit in a long anyway, so 64-bit unsigned multiply is not useful. To implement an unsigned 64-bit division, you could handle it 32 bits as a time, much the way you handled decimal division in grade 4. Check the signs first, if they are 0 just use ordinary division.

You could store a signed or unsigned number in byte, char, int or long.

Sometimes you get the same result in terms of bits whether you treat quantities as signed or unsigned.

For large unsigned numbers, look into BigInteger and a BigDecimal.

Displaying

Java’s Integer.toString interprets the value as signed. Here is how to treat it as unsigned.

/**
 * Convert an unsigned int to a String.
 * @param i the int to convert.
 * @return the equivalent unsigned String
 */
public static void unsignedToString( int i )
   {
   return Long.toString( i & 0xffffffffL )
   }

Gotchas

Working with a mixture of constants and bytes, it is easy to trip up when int constants don’t sign extend and (byte) constants do. Consider this example:

Why?

Gosling, one of the creators of Java, said he left out unsigned types because of the way they complicated the C and C++ languages. They create too many corner cases where gotchas hide.

I see so more problem than with char. Unsigned bytes could be promoted to int, just like char.

I think the reason was the original C had signed bytes. Back then, 7-bit ASCII (American Standard Code for Information Interchange) was in vogue, which did not need the sign bit. The sign bit was free to use as a special flag.