v variable is been initialized

Question

I did not understand the error: v variable is been initialized In the call of the method less(k, v), inside the insert() method, because the variable v is initialized in line above... But even so the compiler gave me the error. My code is to insert a key in two priority queue, I added a test that i am doing with integers.

    public class MedianPQ <Key extends Comparable<Key>>{
      private MaxPq left;
      private MinPq right;

      public MedianPQ(int N, int M) {
        left = new MaxPq(N);
        right = new MinPq(M);
      }

      private boolean less( Key k, Key v) {
        return k.compareTo(v) < 0;
      }

      private boolean great( Key k, Key v) {
        return k.compareTo(v) > 0;
      }

      public void insert(Key k) {
        Key v;
        if( left.isEmpty() && right.isEmpty()) v = k; // initial
        else {
          if( less(k, v) && (left.size() < right.size() + 1)) {   //error
            left.insert(k);
          }
          else if( great(k, v) && (right.size() < left.size() + 1)) {
            right.insert(k);
          }
          else {
            if( left.size() == right.size() + 1) {
              right.insert(v);
              left.insert(k);
              v = (Key)left.max();
            }
            else {
              left.insert(v);
              right.insert(k);
              v = (Key)right.min();
            }
          }
        }
      }

Test:

public static void main(String[] args) {
    MedianPQ median = new MedianPQ(100, 100);
    Random rnd = new Random();
    for( int i = 0; i < 20; i++) {
      median.insert(rnd.nextInt(50));
    }

It's initialized inside an `if` statement. What should the value of `v` be if the `if` expression evaluates to `false`? — 4castle, Apr 03 '18 at 01:36
@4castle I misread the code. But the initialization explanation is correct, only thing is that I don't know what that default value should be. — Tim Biegeleisen, Apr 03 '18 at 01:41
This doesn't make any sense. Why are you reading from `v` before writing to it? — shmosel, Apr 03 '18 at 01:50
Edited my question to be more clear. I don't know how to initialize the variable. — Marcelo de Sousa, Apr 03 '18 at 02:14
@MarcelodeSousa Please consider accepting and / or voting my answer if it has been useful — Héctor M., Apr 03 '18 at 22:03

Héctor M. · Accepted Answer · 2018-04-03T02:00:57.697

1

v is declared as a local variable, but you never assign an initial value before reassigning another value

public void insert(Key k) {

Key v = null;

Or

Key v = new Key();

if( left.isEmpty() && right.isEmpty()) v = k; // initial

else 
{
    if( less(k, v) && (left.size() < right.size() + 1))
    {
        left.insert(k);
    }
    else if( great(k, v) && (right.size() < left.size() + 1)) 
    {
        right.insert(k);
    }
    else 
    {
       if( left.size() == right.size() + 1) 
       {
           right.insert(v);
           left.insert(k);
           v = (Key)left.max();
        }
        else 
        {
           left.insert(v);
           right.insert(k);
           v = (Key)right.min();
        }       
  }

edited Apr 03 '18 at 02:00

answered Apr 03 '18 at 01:38

Héctor M.

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`Key v = null` is not an initialization statement, because it will already default to being `null`. – Tim Biegeleisen Apr 03 '18 at 01:41
2

@TimBiegeleisen Local variables [don't have default values](https://stackoverflow.com/q/415687/5743988). – 4castle Apr 03 '18 at 01:46
@4castle But are you saying that, if checked, it would have a value other than `null`? Then what would that value be? – Tim Biegeleisen Apr 03 '18 at 01:47
@TimBiegeleisen In any situation where the compiler notices it might have to use a default value, the compiler just throws an error, so there's no way to test it. – 4castle Apr 03 '18 at 01:50
@TimBiegeleisen I have always initialized the classes and strings with null, since the values that accept null, must be initialized in this way. Test it yourself and you will see that null is valid as initialization – Héctor M. Apr 03 '18 at 01:53
@4castle I have always initialized the classes and strings with null, since the values that accept null, must be initialized in this way. Test it yourself and you will see that null is valid as initialization – Héctor M. Apr 03 '18 at 01:55

v variable is been initialized

1 Answers1