java - Understanding synchronized blocks -

i have problem understanding why better use synchronized(syncobject) synchronized(this). example, class:

public class pool implements objectpool {     private object[] pool;     private int initialcapacity;     private int available = 0;     private int waiting = 0;     private final object syncobject = new object();      public pool(int initialcapacity) {         this.initialcapacity = initialcapacity;         pool = new object[initialcapacity];      }      public void releaseobject(object o) throws exception {         synchronized (syncobject) {             pool[available] = o;             available++;         }          if (waiting > 0) {             notify();         }     } } 

because if use this, thread trying execute method have wait, whereas if use object lock, restrict critical section.