Java is strictly typed, we cannot store values that do not match the variable type.

int incorrect = "String";

We can only declare a variable once — cannot use the same name more than once.

The value of the variable can be a complex expression, such as an equation, which can be made up of other variables.

Few more notes...

but... Java knows how to convert some tpes

double score =10;

In memory this will be stored as 10.0.

A variable that has not been assigned a value cannot be used in an expression.