CODEWITHSUNDEEP
javadoubletype-conversionlong-integer
dalawh
dalawh

Reputation: 924

Typecasting Different Types into One Type

long is a 64-bit signed two's complement integer. Is Long a 128-bit signed two's complement integer? I just wanted to confirm this before proceeding.

Long l = 6;
int i = 4;
Integer ii = 2;
l += (l/i) * ii;

I was wondering where I would need to typecast in order to get back 3, instead of 2.

I tried the following:

l += (long) (((double) l/i) * ii);

When I typecast l/i with double, I get back 1, instead of 1.5?

Lets say I was to typecast a Long, that was the largest number for a Long, with (long), what would happen since long is a 64-bit signed two's complement integer.

Upvotes: 2

Views: 143

Answers (3)

BlackJoker
BlackJoker

Reputation: 3191

Your (l/i) * ii means power? If so, maybe you should use BigDecimal. By the way, 1/i equals 0; use 1.0/i instead.

Upvotes: 0

ApproachingDarknessFish
ApproachingDarknessFish

Reputation: 14313

long (lower case) is a primitive type 64-bit integer. Long (upper-case) is a reference type (object) that wraps a long (lower-case). So Long's encode their data in a long and are hence 64-bit as well. If you want > 64-bit precision, look into java.math.BigInteger which offers arbitrarily high precision.

Your problem does not come from incorrect casting within the division statement but from the cast to long at the end:

l += (long) (((double) l/i) * ii);
       ^
       here

The result of (((double) l/i) * ii) is a double of value 3.0. Due to the peculiarities of floating-point arithmetic, this becomes 2 when it is cast to a long.

In order to solve this, use Math.round instead of a typecast:

 l += Math.round(((double) l/i) * ii);

Upvotes: 4

autistic
autistic

Reputation: 15642

Long is a class containing constructors, methods, and constants relevant to the long primitive object (eg. Long.MAX_VALUE which will give you the maximum value that a long can represent). When you convert a long to a Long, you're converting from a value type to a reference type. The number of bits used to represent the values won't change.

Upvotes: 0

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