问题
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.
回答1:
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);
回答2:
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.
来源：https://stackoverflow.com/questions/49372970/can-a-local-variable-with-an-inferred-type-be-reassigned-to-a-different-type