Can a local variable with an inferred type be reas

Question

I remember reading somewhere that local variables with inferred types can be reassigned with values of the same type, which would make sense.

var x = 5;
x = 1; // Should compile, no?

However, I'm curious what would happen if you were to reassign x to an object of a different type. Would something like this still compile?

var x = 5;
x = new Scanner(System.in); // What happens?

I'm currently not able to install an early release of JDK 10, and did not want to wait until tomorrow to find out.

Answer 1

Once a var variable has been initialized, you cannot reassign it to a different type as the type has already been inferred.

so, for example this:

var x = 5;
x = 1; 

would compile as x is inferred to be int and reassigning the value 1 to it is also fine as they're the same type.

on the other hand, something like:

var x = 5;
x = "1"; 

will not compile as x is inferred to be int hence assigning a string to x would cause a compilation error.

the same applies to the Scanner example you've shown, it will fail to compile.

Answer 2

Would not compile, throws "incompatible types: Scanner cannot be converted to int". Local variable type inference does not change the static-typed nature of Java. In other words:

var x = 5;
x = new Scanner(System.in);

is just syntactic sugar for:

int x = 5;
x = new Scanner(System.in);