How to differentiate between compile time errors and runtime errors ?

[gurpeet singh]

Im having tough time in understanding questions related to compile time and runtime error. Can you please shed light on this topic as how to proceed in this regard? i have two code listings shown below:

Code Listing 1 :

int i;
     for (i = 0; i < 10; i++) {
System.out.println("Inside loop");
continue;
}

 System.out.println(i);

Code Listing 2:

int j;
 outer:
for (int i=0; i<5; i++) {
for (j=0; j<5; j++) {
System.out.println("Hello");
continue outer;
} // end of inner loop
System.out.println("outer"); // Never prints
}
System.out.println("Good-Bye");
System.out.println(j);

the compiler gives error in Code Listing 2 as to variable j might not have been initialized. Can you please tell me what the compiler thinks when it encounters code listing 1 and 2. And also the generalized version of the problem relating to compile time error and runtime exception. ??

[Prithvi Sehgal]

Dear Gurpreet,

Welcome to JR.

Well, there is a quick pointer. In code listing 1, the compiler will always execute the initialization for i before evaluating the condition.
So it compiles fine. In case-2, initialization of j is conditionally dependent on the outer loop. The compiler is not sure whether the outer
loop will even run or not, so it in such a scenario, it suspects as its dependent on outer loop, it is not necessary that j will initialize that's
why it will give the compile time error.

HTH,