Is there an advantage to use a Synchronized Method instead of a Synchronized Block?

Question

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

Answer 1

I suppose this question is about the difference between Thread Safe Singleton and Lazy initialization with Double check locking. I always refer to this article when I need to implement some specific singleton.

Well, this is a Thread Safe Singleton:

// Java program to create Thread Safe 
// Singleton class 
public class GFG  
{ 
  // private instance, so that it can be 
  // accessed by only by getInstance() method 
  private static GFG instance; 

  private GFG()  
  { 
    // private constructor 
  } 

 //synchronized method to control simultaneous access 
  synchronized public static GFG getInstance()  
  { 
    if (instance == null)  
    { 
      // if instance is null, initialize 
      instance = new GFG(); 
    } 
    return instance; 
  } 
} 

Pros:

1. Lazy initialization is possible.

2. It is thread safe.

Cons:

1. getInstance() method is synchronized so it causes slow performance as multiple threads can’t access it simultaneously.

This is a Lazy initialization with Double check locking:

// Java code to explain double check locking 
public class GFG  
{ 
  // private instance, so that it can be 
  // accessed by only by getInstance() method 
  private static GFG instance; 

  private GFG()  
  { 
    // private constructor 
  } 

  public static GFG getInstance() 
  { 
    if (instance == null)  
    { 
      //synchronized block to remove overhead 
      synchronized (GFG.class) 
      { 
        if(instance==null) 
        { 
          // if instance is null, initialize 
          instance = new GFG(); 
        } 

      } 
    } 
    return instance; 
  } 
} 

Pros:

1. Lazy initialization is possible.

2. It is also thread safe.

3. Performance reduced because of synchronized keyword is overcome.

Cons:

1. First time, it can affect performance.

2. As cons. of double check locking method is bearable so it can be used for high performance multi-threaded applications.

Please refer to this article for more details:

https://www.geeksforgeeks.org/java-singleton-design-pattern-practices-examples/