title: What does "jmap -histo pid" print exactly
body: <p>I am using the command "jmap -histo pid" and want to know what it is exactly telling me.</p>
  
  <p>The output is something like:</p>
  
  <pre><code> num     #instances         #bytes  class name
  ----------------------------------------------
     1:       2284437      262114728  [C
     2:        686409      124390432  [B
     3:        363878       46799288  &lt;constMethodKlass&gt;
     4:        363878       46590464  &lt;methodKlass&gt;
     5:       1817209       43613016  java.lang.String
     6:         34590       37296528  &lt;constantPoolKlass&gt;
     7:        296302       36673344  [I
     8:         34585       33237656  &lt;instanceKlassKlass&gt;
     9:        248731       21559504  [Ljava.lang.Object;
    10:         28200       19991872  &lt;constantPoolCacheKlass&gt;
    11:        563323       13519752  scala.collection.immutable.$colon$colon
    12:         26813       13103488  &lt;methodDataKlass&gt;
    13:        506968       12167232  scala.collection.immutable.HashSet$HashSet1
    14:        200750       10371320  [Lscala.collection.immutable.HashSet;
    15:        114268        9477096  [Lscala.collection.immutable.HashMap;
    16:         92405        7392400  java.lang.reflect.Method
    17:        200953        6430496  scala.collection.immutable.HashMap$HashMap1
  </code></pre>
  
  <p>By example: What's "bytes" exactly displaying?</p>
  
  <ol>
  <li>Is it the average size per instance of this type</li>
  <li>Is it the total size of all objects which were created since start of the app</li>
  <li>Is it the current allocated size in the heap of all objects</li>
  </ol>
  
  <p>Maybe someone can explain to me what's "#instances" aswell. </p>