class Test {
    static void test(int p) {
	int n;
	p = p - 1;
	if (p > 0) {
	    n = 100;
	}
	while (n != 0) {
	    System.out.println(n);
	    n = n - p;
	}
    }
}

What does compiler do with the above program?

laralaptop03:~/t$ javac Test.java 
Test.java:8: variable n might not have been initialized
	while (n > 0) {
               ^
1 error

Corrected program:

class Test {
    static void test(int p) {
	int n;
	p = p - 1;
	if (p > 0) {
	    n = 100;
	}
	else {
	    n = -100;
	}
	while (n != 0) {
	    System.out.println(n);
	    n = n - p;
	}
    }
}

We would like variables to be initialized on all execution paths. Otherwise, the program execution could be undesirable affected by the value that was in the variable initially:

• junk value that was there in the memory
• a value that an attacker purposely put into memory, especially in the presence of
  • buffer overlow
  • stack buffer overflow
  • other cases of unusual language design decisions
    • do not require variables to be declared before use
    • allow URL argument to set initial values of global variables
    • no checking if variable is initialized
    • a typo in variable name leads to attacker being able to set initial values of variables

A tool that checks PHP errors, including initialization: Phantm