title: java - 2D array find random null value
body: <p>I have a 2D array in which are some indexes null and some of indexes have value.
  I want to select a random index that contains null.</p>
  
  <p>example</p>
  
  <pre><code>5,0,0,5,0
  4,0,0,4,7
  9,0,4,8,9
  0,8,4,0,1
  </code></pre>
  
  <p>i want to choose random index from these which are zero</p>
  
  <p>thx for reply</p>