浮点到整数vs整数到浮点自动转换

Question

I'm studying java by Herbert Schildt's "Java for beginners" book. It is said that, being a destiny variable compatible and sufficiently big to store an origin one, an automatic conversion is done.

That being said, an Int should be able to store an Float and vice-versa, since they both have a 4 bytes size.

public class MyClass {
    public static void main(String args[]) {
        int i = 10;
        float f = i;

        float ff = 10;
        int ii = ff; 
    }
}

However, when compiled, this piece of code generetes the following error:

/MyClass.java:15: error: incompatible types: possible lossy conversion from float to int
        int ii = ff; 
                 ^
1 error

Why is there that, being a compatible type and sufficiently big to store each other, a float can store an int but an int cannot store a float?

Answer 1

Because float contains numbers also after the decimal point and int does not. Without this you shouldn't be able to simply trim the decimal part from the number by explicitly casting the float to int too.

Answer 2

As you can see, you can store a int into a float , but you can't put a float inside a int .

This heappens because the internal structure of float is a decimal number and int, as its name says, is integer.

For more information you can take a look into this discussion about How are floating point numbers are stored in memory .

Answer 3

an Int should be able to store an Float and vice-versa, since they both have a 4 bytes size.

The size of the data is not the important part. Rather it is about the values which can be stored in the give number of bytes. int can only store whole number values between -2^31 and 2^31-1. On the other hand, float can store decimal values.

Answer 4

Int to float is never a lossy conversion if the integer value will be within the range of maximum integer value that float can store as value will always be stored/converted to <intvalue>.0 like 4 will be stored as 4.0 . But in case of conversion from float to int, your fraction value will be lost so JVM gives you such error. If you can take such risk then you have to explicitly convert the float value into int.