Why --i and i-1 producing diffrent output in recursion?

Question

I have two method, the difference is one is having --i1 and other is having i-1, however they are producing different output.

 String s1 = "axbdcg";
        String s2 ="aazzzzzzzzzzzzcbc";
        System.out.println(method(s1,s2,s1.length()-1,s2.length()-1));


 int method(String s1, String s2, int i1, int i2){
    if(s1.length() == 0 || s2.length() == 0) return 0;
    if(i1 < 0|| i2 < 0) return 0;
    if(s1.charAt(i1) ==  s2.charAt(i2)) return 1+  method(s1,s2,--i1,--i2);
int left = method(s1,s2,--i1,i2);

int right =  method(s1,s2,i1,--i2);
         return Math.max(left ,right);
    }

this method is giving 2 as output and

     int method(String s1, String s2, int i1, int i2){
    if(s1.length() == 0 || s2.length() == 0) return 0;
    if(i1 < 0|| i2 < 0) return 0;
    if(s1.charAt(i1) ==  s2.charAt(i2)) return 1+  method(s1,s2,--i1,--i2);
int left = method(s1,s2,i1-1,i2);

int right =  method(s1,s2,i1,--i2);
         return Math.max(left ,right);
    }

is giving 3 as output.

Answer 1

foo(--i) means following:

1. decrement i with -1
2. assign a new value to i
3. put modified value i to the method foo()

P.S. i is modified

---

foo(i - 1) means following:

1. decrement i with -1
2. put modified value i to the method foo()

P.S. i is not modified

---

So the difference is when you call method(s1,s2,i1,--i2) in the first snippet, i is being changed, but in the second one - is not.