Java Big Integer Value

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Dyuman Joshi
Dyuman Joshi 2022-2-1
评论： Dyuman Joshi 2022-2-15
Ran in:
I was working with BigIntegers to solve a problem on Cody, where I got stuck upon something.
import java.math.*
BigInteger(10)
ans = 10
BigInteger(1234)
ans = -46
BigInteger(num2str(1234))
ans = 1234
I tried to find why this happens but I couldn't find any useful resources. I have no knowledge of Java if anyone needs to know.
Is the default input to BigInteger a string/character array? (Which I suspect so)
Also an odd behaviour (which I don't understand)? Can someone explan why this happens?
for i=1:11
BigInteger(2^i+1)
end
ans = 3 ans = 5 ans = 9 ans = 17 ans = 33 ans = 65 ans = -127 ans = 1 ans = 1 ans = 1 ans = 1

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Walter Roberson
Walter Roberson 2022-2-1
https://docs.oracle.com/javase/7/docs/api/java/math/BigInteger.html
The single-parameter form of BigInteger with a numeric parameter is
"BigInteger(byte[] val)
Translates a byte array containing the two's-complement binary representation of a BigInteger into a BigInteger."
So when you pass in a numeric value, it converts the numeric value to a signed byte.
When you pass in the result of num2str() you are using a different constructor,
"BigInteger(String val)
Translates the decimal String representation of a BigInteger into a BigInteger."
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Walter Roberson
Walter Roberson 2022-2-15
One byte holds 8 bits, and 2^8 = 256 .
The BigInteger class always uses full bytes -- you cannot define a BigInteger that is (for example) 11 bits long
Dyuman Joshi
Dyuman Joshi 2022-2-15
That makes it clear, thanks!

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