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synchronized block vs synchronized method?

0 votes

Can any one tell me the advantage of synchronized method over synchronized block with an example?Thanks.

asked Nov 14, 2011 in Java/J2EE by anonymous
    

1 Answer

0 votes

Synchronized Method

Pros:

  • Your IDE can indicate the synchronized methods.
  • The syntax is more compact.
  • Forces to split the synchronized blocks to separate methods.

Cons:

  • Synchronizes to this and so makes it possible to outsiders to synchronize to it too.
  • It is harder to move code outside the synchronized block.

Synchronized block

Pros:

  • Allows using a private variable for the lock and so forcing the lock to stay inside the class.
  • Synchronized blocks can be found by searching references to the variable.

Cons:

  • The syntax is more complicated and so makes the code harder to read.

Synchronized method is used for lock all the objects Synchronized block is used to lock specific object

Synchronized blocks place locks for shorter periods than synchronized methods.

With synchronized blocks, you can have multiple synchronizers, so that multiple simultaneous but non-conflicting things can go on at the same time.

Most often I use this to synchronize access to a list or map but I don't want to block access to all methods of the object.

In the following code one thread modifying the list will not block waiting for a thread that is modifying the map. If the methods were synchronized on the object then each method would have to wait even though the modifications they are making would not conflict.

private List<Foo> myList = new ArrayList<Foo>);
private Map<String,Bar) myMap = new HashMap<String,Bar>);

public void put( String s, Bar b ) {
  synchronized( myMap ) {
    myMap.put( s,b );
    // then some thing that may take a while like a database access or RPC or notifying listeners
  }
}

public void hasKey( String s, ) {
  synchronized( myMap ) {
    myMap.hasKey( s );
  }
}

public void add( Foo f ) {
  synchronized( myList ) {
    myList.add( f );
// then some thing that may take a while like a database access or RPC or notifying listeners
  }
}

public Thing getMedianFoo() {
  Foo med = null;
  synchronized( myList ) {
    Collections.sort(myList);
    med = myList.get(myList.size()/2);
  }
  return med;
}

answered Nov 15, 2011 by sarada Hot Users (2,340 points)
Can we make a constructor synchronized?
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