A2Z Java Interview Prep

Singleton Design Pattern Problem: Ensure a class has only one instance and provide a global point of access to that instance. Solution: Create a class with a private constructor, a private static instance variable, and a public static method to provide access to the single instance. Key Points to Make a Singleton Class in Java: Private constructor to prevent external instantiation. Private static instance variable to hold the single instance. Public static method to provide access to the instance. Ways to Break a Singleton: Reflection: Using reflection to access the private constructor. Serialization: When a Singleton is serialized and deserialized, it creates a new instance. Cloning: Creating a clone of the Singleton instance. Prevention Techniques: Lazy Initialization with Double-Checked Locking: Use double-checked locking for lazy initialization to ensure thread safety. Enum Singleton: Implement the Singleton using an enum to handle serialization, reflection, and cloning. Ove...

Proxy Design Pattern Problem: Control access to an object by providing a surrogate or placeholder for it. Solution: Create a proxy class that acts as an intermediary between the client and the actual object. The proxy can perform additional operations before or after forwarding the request to the real object. Key Points to Implement a Proxy: Proxy class implementing the same interface as the real object. Proxy holds a reference to the real object. Proxy controls access to the real object and may perform additional actions. Predefined Use-Case in Java: A common use of the Proxy pattern is the java.lang.reflect.Proxy class, which allows the creation of dynamic proxy instances for interfaces at runtime. Example Program: interface Internet { void connectTo(String serverHost) throws Exception; } class RealInternet implements Internet { @Override public void connectTo(String serverHost) { System.out.println("Connecting to " + serverHost); } } class Prox...