We Keep Coding

Is there an equivalent java constant for go's MaxUint64

go has the constant MaxUint32, for insigned integers, but does Java have an equivalent constant? Cuz I noticed that MaxUint32 is 4294967295 and Integer.MAX_VALUE is 2x that.
What would be the java equivalent of
r := float64(stringHash(source)) / (float64(math.MaxUint32) + 1)
What's the difference between a float in Java and a float64 in go?

According to this Question on Stack Overflow, MaxUint32 is a constant for the maximum 32-bit number available within in the Go type system, ranging from 0 to 4,294,967,295.
As for Java, I can explain that Java has only signed numeric types. As commented by tgdavies, that means the largest signed 32-bit integer in Java is half that of the unsigned 32-bit integer in Go: 2,147,483,647. As a workaround for compatibility with Go, just us a 64-bit long in Java to accommodate values coming in from Go.
In recent years a facility was added to address numbers as if unsigned. But I believe that should be used only on an exceptional basis. See Declaring an unsigned int in Java, especially this Answer.
And I can quote from The Java Tutorials, provided free-of-cost by Oracle corp, which you should read before posting here on basic Java matters:
The eight primitive data types supported by the Java programming language are:
byte: The byte data type is an 8-bit signed two's complement integer. It has a minimum value of -128 and a maximum value of 127 (inclusive). The byte data type can be useful for saving memory in large arrays, where the memory savings actually matters. They can also be used in place of int where their limits help to clarify your code; the fact that a variable's range is limited can serve as a form of documentation.
short: The short data type is a 16-bit signed two's complement integer. It has a minimum value of -32,768 and a maximum value of 32,767 (inclusive). As with byte, the same guidelines apply: you can use a short to save memory in large arrays, in situations where the memory savings actually matters.
int: By default, the int data type is a 32-bit signed two's complement integer, which has a minimum value of -231 and a maximum value of 231-1. 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. Use the Integer class to use int data type as an unsigned integer. See the section The Number Classes for more information. Static methods like compareUnsigned, divideUnsigned etc have been added to the Integer class to support the arithmetic operations for unsigned integers.
long: The long data type is a 64-bit two's complement integer. The signed long has a minimum value of -263 and a maximum value of 263-1. In Java SE 8 and later, you can use the long data type to represent an unsigned 64-bit long, which has a minimum value of 0 and a maximum value of 264-1. Use this data type when you need a range of values wider than those provided by int. The Long class also contains methods like compareUnsigned, divideUnsigned etc to support arithmetic operations for unsigned long.
float: The float data type is a single-precision 32-bit IEEE 754 floating point. Its range of values is beyond the scope of this discussion, but is specified in the Floating-Point Types, Formats, and Values section of the Java Language Specification. As with the recommendations for byte and short, use a float (instead of double) if you need to save memory in large arrays of floating point numbers. This data type should never be used for precise values, such as currency. For that, you will need to use the java.math.BigDecimal class instead. Numbers and Strings covers BigDecimal and other useful classes provided by the Java platform.
double: The double data type is a double-precision 64-bit IEEE 754 floating point. Its range of values is beyond the scope of this discussion, but is specified in the Floating-Point Types, Formats, and Values section of the Java Language Specification. For decimal values, this data type is generally the default choice. As mentioned above, this data type should never be used for precise values, such as currency.
boolean: The boolean data type has only two possible values: true and false. Use this data type for simple flags that track true/false conditions. This data type represents one bit of information, but its "size" isn't something that's precisely defined.
char: The char data type is a single 16-bit Unicode character. It has a minimum value of '\u0000' (or 0) and a maximum value of '\uffff' (or 65,535 inclusive).
That last one, char, is legacy, and should generally be avoided in favor of using code point integer numbers.
All of those primitive types have wrapper classes, when you need an object.
For extra large integers, use BigInteger class.
For extra large/small fractional numbers, use BigDecimal. Also use BigDecimal when you need accuracy rather than speed-of-execution. Uses cases include fractional money matters.

Unsigned long in Java

Currently, I am using signed values, -2^63 to 2^63-1. Now I need the same range (2 * 2^64), but with positive values only. I found the java documentations mentioning unsigned long, which suits this use.
I tried to declare 2^64 to a Long wrapper object, but it still loses the data, in other words, it only captures till the Long.MAX_VALUE, so I am clearly missing something.
Is BigInteger the signed long that Java supports?
Is there a definition or pointer as to how to declare and use it?

In Java 8, unsigned long support was introduced. Still, these are typical longs, but the sign doesn't affect adding and subtracting. For dividing and comparing, you have dedicated methods in Long. Also, you can do the following:
long l1 = Long.parseUnsignedLong("12345678901234567890");
String l1Str = Long.toUnsignedString(l1)
BigInteger is a bit different. It can keep huge numbers. It stores them as int[] and supports arithmetic.

Although Java has no unsigned long type, you can treat signed 64-bit two's-complement integers (i.e. long values) as unsigned if you are careful about it.
Many primitive integer operations are sign agnostic for two's-complement representations. For example, you can use Java primitive addition, subtraction and multiplication on an unsigned number represented as a long, and get the "right" answer.
For other operations such as division and comparison, the Long class provides method like divideUnsigned and compareUnsigned that will give the correct results for unsigned numbers represented as long values.
The Long methods supporting unsigned operations were added in Java 8. Prior to that, you could use 3rd-party libraries to achieve the same effect. For example, the static methods in the Guava UnsignedLongs class.
Is BigInteger the signed long that Java supports?
BigInteger would be another way to represent integer values greater that Long.MAX_VALUE. But BigInteger is a heavy-weight class. It is unnecessary if your numbers all fall within the range 0 to 264 - 1 (inclusive).

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...
UByte b = ubyte(1);
UShort s = ushort(1);
UInteger i = uint(1);
ULong l = ulong(1);
All of these types extend java.lang.Number and can be converted into higher-order primitive types and BigInteger. In your case, earlier versions of jOOU simply stored the unsigned long value in a BigInteger. Version 0.9.3 does some cool bit shifting to fit the value in an ordinary long.
(Disclaimer: I work for the company behind these libraries)

Equivalent Data Types in Java

I am developing an Android application and it is dealing with BigML big data server. I need to parse the data in the following formats.
int16
int8
What are the equivalent data types in Java/Android for the above mentioned types?

There are no unsigned data types in Java.
So if you are looking for signed types then int8 -> byte and int16 -> short
They only contain positive values, with 0. So, it is 'unsigned' right?
Yes then they are unsigned, but as I already told you Java does not support unsigned types. So what you can do is use int8 -> short and int16 -> int

Java Primitive Data Types
byte: The byte data type is an 8-bit signed two's complement integer. It has a minimum value of -128 and a maximum value of 127 (inclusive). The byte data type can be useful for saving memory in large arrays, where the memory savings actually matters. They can also be used in place of int where their limits help to clarify your code; the fact that a variable's range is limited can serve as a form of documentation.
short: The short data type is a 16-bit signed two's complement integer. It has a minimum value of -32,768 and a maximum value of 32,767 (inclusive). As with byte, the same guidelines apply: you can use a short to save memory in large arrays, in situations where the memory savings actually matters.

In Java an int8 would be a byte, and you can use short for int16.

Integer range when using 64bit jdk

As I understand the difference between two integer from 32bit & 64bit are the following:
32bit range −2,147,483,648 to 2,147,483,647
64bit range: −9,223,372,036,854,775,808 to +9,223,372,036,854,775,807
I am using a 64bit jdk, I validate it by printing the following:
System.out.println("JVM Bit size: " + System.getProperty("sun.arch.data.model"));
JVM Bit size: 64
when I try to init a new Integer variable with number bigger ther 10 letters I get a compilation error. why is that? it looks like the 64bit is larger
example (ran on netbeans):
int x = 12345678910; => Error: integer is too large

The size of an int in Java is completely independent of the 32-bitness or 64-bitness of a JDK. It is always 4 bytes = 32 bits = −2,147,483,648 to 2,147,483,647.
If you want a 64-bit integer, use a long, which is always 64 bits = 8 bytes.

Unlike other languages, Java's numeric primitive types are always the same size, whatever the platform (32bit or 64bit, LE or BE); they are all big endian and are 1 byte long for byte, 2 bytes long for short and char, 4 bytes long for int and 8 bytes long for long.
If it were not the case, jars would not be portable across platforms...

Your best resource is JLS:
The integral types are byte, short, int, and long, whose values are 8-bit, 16-bit, 32-bit and 64-bit signed two's-complement integers, respectively, and char, whose values are 16-bit unsigned integers representing UTF-16 code units
4.2.1. Integral Types and Values
The values of the integral types are integers in the following ranges:
For byte, from -128 to 127, inclusive
For short, from -32768 to 32767, inclusive
For int, from -2147483648 to 2147483647, inclusive
For long, from -9223372036854775808 to 9223372036854775807, inclusive
For char, from '\u0000' to '\uffff' inclusive, that is, from 0 to 65535

Declaring an unsigned int in Java

Is there a way to declare an unsigned int in Java?
Or the question may be framed as this as well:
What is the Java equivalent of unsigned?
Just to tell you the context I was looking at Java's implementation of String.hashcode(). I wanted to test the possibility of collision if the integer were 32 unsigned int.

Java does not have a datatype for unsigned integers.
You can define a long instead of an int if you need to store large values.
You can also use a signed integer as if it were unsigned. The benefit of two's complement representation is that most operations (such as addition, subtraction, multiplication, and left shift) are identical on a binary level for signed and unsigned integers. A few operations (division, right shift, comparison, and casting), however, are different. As of Java SE 8, new methods in the Integer class allow you to fully use the int data type to perform unsigned arithmetic:
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 2^32-1. Use the Integer class to use int data type as an unsigned integer. Static methods like compareUnsigned, divideUnsigned etc have been added to the Integer class to support the arithmetic operations for unsigned integers.
Note that int variables are still signed when declared but unsigned arithmetic is now possible by using those methods in the Integer class.

Whether a value in an int is signed or unsigned depends on how the bits are interpreted - Java interprets bits as a signed value (it doesn't have unsigned primitives).
If you have an int that you want to interpret as an unsigned value (e.g. you read an int from a DataInputStream that you know should be interpreted as an unsigned value) then you can do the following trick.
int fourBytesIJustRead = someObject.getInt();
long unsignedValue = fourBytesIJustRead & 0xffffffffL;
Note, that it is important that the hex literal is a long literal, not an int literal - hence the 'L' at the end.

We needed unsigned numbers to model MySQL's unsigned TINYINT, SMALLINT, INT, BIGINT in jOOQ, which is why we have created jOOU, a minimalistic library offering wrapper types for unsigned integer numbers in Java. Example:
import static org.joou.Unsigned.*;
// and then...
UByte b = ubyte(1);
UShort s = ushort(1);
UInteger i = uint(1);
ULong l = ulong(1);
All of these types extend java.lang.Number and can be converted into higher-order primitive types and BigInteger. Hope this helps.
(Disclaimer: I work for the company behind these libraries)

For unsigned numbers you can use these classes from Guava library:
UnsignedInteger
UnsignedLong
They support various operations:
plus
minus
times
mod
dividedBy
The thing that seems missing at the moment are byte shift operators. If you need those you can use BigInteger from Java.

Perhaps this is what you meant?
long getUnsigned(int signed) {
return signed >= 0 ? signed : 2 * (long) Integer.MAX_VALUE + 2 + signed;
}
getUnsigned(0) → 0
getUnsigned(1) → 1
getUnsigned(Integer.MAX_VALUE) → 2147483647
getUnsigned(Integer.MIN_VALUE) → 2147483648
getUnsigned(Integer.MIN_VALUE + 1) → 2147483649

Use char for 16 bit unsigned integers.

There are good answers here, but I don’t see any demonstrations of bitwise operations. Like Visser (the currently accepted answer) says, Java signs integers by default (Java 8 has unsigned integers, but I have never used them). Without further ado, let‘s do it...
RFC 868 Example
What happens if you need to write an unsigned integer to IO? Practical example is when you want to output the time according to RFC 868. This requires a 32-bit, big-endian, unsigned integer that encodes the number of seconds since 12:00 A.M. January 1, 1900. How would you encode this?
Make your own unsigned 32-bit integer like this:
Declare a byte array of 4 bytes (32 bits)
Byte my32BitUnsignedInteger[] = new Byte[4] // represents the time (s)
This initializes the array, see Are byte arrays initialised to zero in Java?. Now you have to fill each byte in the array with information in the big-endian order (or little-endian if you want to wreck havoc). Assuming you have a long containing the time (long integers are 64 bits long in Java) called secondsSince1900 (Which only utilizes the first 32 bits worth, and you‘ve handled the fact that Date references 12:00 A.M. January 1, 1970), then you can use the logical AND to extract bits from it and shift those bits into positions (digits) that will not be ignored when coersed into a Byte, and in big-endian order.
my32BitUnsignedInteger[0] = (byte) ((secondsSince1900 & 0x00000000FF000000L) >> 24); // first byte of array contains highest significant bits, then shift these extracted FF bits to first two positions in preparation for coersion to Byte (which only adopts the first 8 bits)
my32BitUnsignedInteger[1] = (byte) ((secondsSince1900 & 0x0000000000FF0000L) >> 16);
my32BitUnsignedInteger[2] = (byte) ((secondsSince1900 & 0x000000000000FF00L) >> 8);
my32BitUnsignedInteger[3] = (byte) ((secondsSince1900 & 0x00000000000000FFL); // no shift needed
Our my32BitUnsignedInteger is now equivalent to an unsigned 32-bit, big-endian integer that adheres to the RCF 868 standard. Yes, the long datatype is signed, but we ignored that fact, because we assumed that the secondsSince1900 only used the lower 32 bits). Because of coersing the long into a byte, all bits higher than 2^7 (first two digits in hex) will be ignored.
Source referenced: Java Network Programming, 4th Edition.

It seems that you can handle the signing problem by doing a "logical AND" on the values before you use them:
Example (Value of byte[] header[0] is 0x86 ):
System.out.println("Integer "+(int)header[0]+" = "+((int)header[0]&0xff));
Result:
Integer -122 = 134

Just made this piece of code, wich converts "this.altura" from negative to positive number. Hope this helps someone in need
if(this.altura < 0){
String aux = Integer.toString(this.altura);
char aux2[] = aux.toCharArray();
aux = "";
for(int con = 1; con < aux2.length; con++){
aux += aux2[con];
}
this.altura = Integer.parseInt(aux);
System.out.println("New Value: " + this.altura);
}

You can use the Math.abs(number) function. It returns a positive number.