Play with Unsigned Integers in Java
For basic knowledge of data types in Java, please see here.
There is no unsigned integral type in Java. In Java SE 8 and later, however, we could use int and long to represent unsined integers, with the range of 0 ~ 2{32}-1 (32 bits) and 0 ~ 2{64}-1 (64 bits). And the Integer and Long class also contains methods like compareUnsigned and divideUnsigned etc to support arithmetic perations for unsigned integers.
Let's play with these methods!
Below are some examples for toUnsignedLong, toUnsignedString, parseUnsignedInt, compareUnsigned, divideUnsigned, remainderUnsigned methods, and also the comparisons between them and the ones for signed integers. IntegralType.print is a function to print out 32-bit binary representation for int and 64-bit for long, please see details here. I wrote results in the console as comments.
int x = 5;
int y = -2;
String s = "11111111111111111111111111111110";
long z = -2L;
IntegralType.print("x =", x); //x = 00000000000000000000000000000101 = 5
IntegralType.print("y =", y); //y = 11111111111111111111111111111110 = -2
IntegralType.print("(unsigned) y =", Integer.toUnsignedLong(y)); //(unsigned) y = 0000000000000000000000000000000011111111111111111111111111111110 = 4294967294
IntegralType.print("z =", z); //z = 1111111111111111111111111111111111111111111111111111111111111110 = -2
System.out.println("(unsigned) z =" + Long.toBinaryString(z) + " = " + Long.toUnsignedString(z)); //(unsigned) z =1111111111111111111111111111111111111111111111111111111111111110 = 18446744073709551614
IntegralType.print("y =", Integer.parseInt("-2")); //y = 11111111111111111111111111111110 = -2
IntegralType.print("y =", Integer.parseInt("-10", 2)); //y = 11111111111111111111111111111110 = -2
//IntegralType.print("y =", Integer.parseInt(s, 2)); //Wrong!!!
//IntegralType.print("y = ", Integer.parseUnsignedInt("-2")); //Wrong!!!
IntegralType.print("y =", -Integer.parseUnsignedInt("2")); //y = 11111111111111111111111111111110 = -2
//IntegralType.print("y =", Integer.parseUnsignedInt("-10", 2)); //Wrong!!!
IntegralType.print("y =", Integer.parseUnsignedInt(s, 2)); //y = 11111111111111111111111111111110 = -2
System.out.println("Compare x and y: " + Integer.compare(x, y)); //Compare x and y: 1
System.out.println("Unsigned Compare x and y: "+Integer.compareUnsigned(x, y)); //Unsigned Compare x and y: -1
System.out.println("x/y= "+x/y); //x/y= -2
System.out.println("x%y = "+x%y); //x%y = 1
System.out.println("(unsigned) x/y = "+Integer.divideUnsigned(x, y)); //(unsigned) x/y = 0
System.out.println("(unsigned) x%y = "+Integer.remainderUnsigned(x, y)); //(unsigned) x%y = 5
System.out.println("y/x= "+y/x); //y/x= 0
System.out.println("y%x = "+y%x); //y%x = -2
System.out.println("(unsigned) y/x = "+Integer.divideUnsigned(y, x)); //(unsigned) y/x = 858993458
System.out.println("(unsigned) y%x = "+Integer.remainderUnsigned(y, x)); //(unsigned) y%x = 4
Integer.parseInt(s, 2) tends to parse s as a signed integer in radix 2. You could initialize an int as int i = 0b11111111111111111111111111111110, where i is actually -2. For parseInt, however, Java will consider "11111111111111111111111111111110" as 4294967294, which is larger than the maximum int. So this line will cause an NumberFormatException. The right way is to input a human-readable string representing a negetive int like Integer.parseInt("-10", 2).
Integer.parseUnsignedInt("-2") doesn't work because -2 is less than the minimun unsigned int 0. The same reason goes to Integer.parseUnsignedInt("-10", 2).