design patterns in java interview questions

#Design patterns in java interview questions how to
#Design patterns in java interview questions code

By the way using Java enum to create thread-safe singleton is the most simple way. There are multiple ways to write thread-safe singleton in Java e.g by writing singleton using double checked locking, by using static Singleton instance initialized during class loading. Can you write thread-safe Singleton in Java?

#Design patterns in java interview questions how to

See How to use Decorator pattern in Java for more details. BufferedReader and BufferedWriter are a good example of decorator pattern in Java. This is the easiest method but it has a drawback that instance is created even though it might not be using it by any client.Decorator pattern is another popular Java design pattern question which is common because of its heavy usage in java.io package. In eager initialization, the instance of Singleton Class is created at the time of class loading. Question: What is eager initialization in singleton? Question: Can we create a clone of a singleton object? Answer: Yes, it is possible Question: How to prevent cloning of a singleton object? Answer: By throwing an exception within the body of the clone() method. Question: Can you write thread-safe Singleton in Java? There are multiple ways to write thread-safe singleton in Java Question: If the singletons getInstance is not synchronized, how it would behave in multithreaded environment? Answer: Threads can be unpredictable, we can't guarantee when the method is unsynchronized it would give max of two singleton instance. By the way using Java enum to create thread-safe singleton this is most simple way.

By using static Singleton instance initialized during class loading.

By writing singleton using double checked locking.

There are multiple ways to write thread-safe singleton in Java Question: Can you write thread-safe Singleton in Java? Singleton objects can be created in two ways. Question: In how many ways can you create singleton pattern in Java?

Clients may only use the accessor function to manipulate the Singleton.Define all constructors to be protected or private.Do 'lazy initialization' (creation on first use) in the accessor function.Define a public static accessor function in the class.Define a private static attribute in the 'single instance' class.Implementation in Java: Step 1: Creating a Singleton Class. Global access is not otherwise provided for.Ownership of the single instance cannot be reasonably assigned.Singleton encapsulates 'just-in-time initialization' of the objectĬonditions: Singleton should only be considered if following criteria are satisfied:.Singleton ensures that a class has only one instance, and provide a global point of access to this instance.Question: What is a Singleton design pattern? Singleton pattern is one of the simplest design pattern.It is used when an application needs one, and only one, instance of an object of class. Makes it almost impossible to subclass a Singleton.

#Design patterns in java interview questions code

Creates tightly coupled code that is difficult to test.

Encourages using a global shared instance which prevents an object and resources used by this object from being deallocated.Violates Single Responsibility Principle (SRP) by controlling their own creation and lifecycle.when the sole instance should be extensible by subclassing, and clients should be able to use an extended instance without modifying their code.There must be exactly one instance of a class, and it must be accessible to clients from a well-known access point.When to use Singleton? Use the Singleton when It ensures that a class has only one instance, and provides a global point of access to it.