Simple Java integer and long arithmetics

Question

Simple code no problem

long x =  Integer.MAX_VALUE;
System.out.println(x * 2 + "...." + Long.MAX_VALUE);

= 4294967294....9223372036854775807

but what is happening here? why -2

System.out.println(2 * Integer.MAX_VALUE + "...." + Long.MAX_VALUE);
=   -2....9223372036854775807

and why elements is 149998, doesn't the compiler converts these to long?

    long elements = 2 * Integer.MAX_VALUE + 150000;
System.out.println(elements + "...." + Long.MAX_VALUE);
149998....9223372036854775807

-thanks

Answer 1

and why elements is 149998, doesn't the compiler converts these to long?

It does, but only after the arithmetic. So you've got int*int + int, which is an int. It will then cast it to a long. However, at this point you've got an integer overflow (i.e. it went beyond the bounds of an integer)

you need to convert the numbers of the right to a long first

long elements = 2L * Integer.MAX_VALUE + 150000;

or

long elements = 2 * (long)Integer.MAX_VALUE + 150000;

B

Answer 2

Promote variables from integer to long.

long elements = 2 * Integer.MAX_VALUE + 150000; 

should be

long elements = 2L * Integer.MAX_VALUE + 150000;

The evaluation of original statement,

long elements = 2 * Integer.MAX_VALUE + 150000; 

is equivalent to

long elements = (long)(2 * Integer.MAX_VALUE + 150000); 

Answer 3

Integer.MAX_VALUE =2147483647=01111111 11111111 11111111 11111111 

And

2*Integer.MAX_VALUE=4294967294=2*(01111111 11111111 11111111 11111111)  
                              =this will result a 33-bit value

But in Java int can represent maximum of 32bit.

Answer 4

I don't have enough rep to comment yet :(.

The Oracle Java Tutorials confirmed that it will convert the data to the primitive type long. Since you're adding an int and a long, the compiler will add the data before it converts it to a long. If you really want it to be a long the entire time, you'd have to type cast.

EX;

 // (long) is typcasted
long elements = 2 * (long) Integer.MAX_VALUE + 150000;

//prints elements as a long t + "" + max value
System.out.println(elements + "...." + Long.MAX_VALUE); 

Type is casting preformed by adding the wanted primitive type in front of the current data type.