Java: Error: variable might not have been initialized

Question

I'm learning Java and I'm getting this error. I know this has been asked a few (a lot of) times but none of the answers seems to answer my question. The body of the code is:

String[] number = {"too small", "one", "two", "three", "four", "too large"};
int i;
if(num<1){
    i=0;
}
if(num==1){
    i=1;
}
if(num==2){
    i=2;
}
if(num==3){
    i=3;
}
if(num==4){
    i=4;
}
if(num>4){
    i=5;
}
return number[i];

where the variable 'num' is declared, initialized and given previously. The error I get is: "Variable 'i' might not have been initialized" and pointing to the last line (return number[i];).

The thing is, if I declare 'i' and immediately assign a value (int i=0;) the code runs fine. But if I don't assign a value I get the error EVEN if a possible value is assigned after each 'if'.

I don't get this kind of error with C, for example.

Thanks

Answer 1

Java doesn't analyze the logic of your if blocks determine that one of your if statements will run and assign a value to i. It is simple and it sees the possibility of none of the if statements running. In that case, no value is assigned to i before it's used.

Java will not give a default value to a local variable, even if it gives default values to class variables and instance variables. Section 4.12.5 of the JLS covers this:

Every variable in a program must have a value before its value is used:

and

A local variable (§14.4, §14.14) must be explicitly given a value before it is used, by either initialization (§14.4) or assignment (§15.26)

Assign some kind of default value to i, when you declare it, to satisfy the compiler.

int i = 0;
// Your if statements are here.
return number[i];