Floating point arithmetic not working as expected [duplicate]

Question

The following simple floating point arithmetic operation is not working as expected.

double den = (1+j);
System.out.println(den);
den = 1/den;
System.out.println(den);

double newden = 1/(1+j);
System.out.println(newden);

The above code gives the following output.

7.0
0.14285714285714285
0.0

As shown above, the first two operations work as expected but the last doesn't. I suppose that it has something to do with the variable type but still haven't figured out the problem.

Can you please explain the behaviour of arithmetic operations in Java?

Answer 1

An arithmetic operation in java is done in int if there is no float/double/long involved. Hence, change one of the arg to float/double and it works as expected.

The following code would work:

double newden = 1d/(i+j);
System.out.println(newden);

---

From the java spec:

Widening primitive conversion (§5.1.2) is applied to convert either or both operands as specified by the following rules, in order:

• If either operand is of type double, the other is converted to double.
• Otherwise, if either operand is of type float, the other is converted to float.
• Otherwise, if either operand is of type long, the other is converted to long.
• Otherwise, both operands are converted to type int.

Answer 2

This is working. If you try this by putting (double) 1/(1+j); there, you can see the result:

int j = 1;
        double den = (1+j);
        System.out.println(den);
        den = 1/den;
        System.out.println(den);

        double newden = (double) 1/(1+j);
        System.out.println(newden);

Here, your output will be:

2.0
0.5
0.5