UNIT-1

By: Dr. Pankaj Malik UNIT - 1 1. What is Java Generics? Java Generics is a feature in Java that allows for type safety and improved code reusability. It provides a way to specify the type of data that can be stored in a collection or passed as an argument to a method. This improves type safety by preventing incorrect type assignments, reducing the need for typecasting, and allowing for more efficient code. 2. What is the purpose of generics in Java? The purpose of generics in Java is to provide type safety and improved code reusability. They allow developers to specify the type of data that can be stored in a collection or passed as an argument to a method, improving type safety and reducing the need for typecasting. This results in more efficient and maintainable code. 3. What is type parameterization in Java? Type parameterization in Java refers to the process of defining a generic type by specifying the type parameter that will be used. This allows for a single class, method, or interface definition to be reused for different types of data. When a generic type is instantiated, the programmer specifies the actual type to be used in place of the type parameter. This allows for type safety and improved code reusability, as the same code can be used for multiple types of data, reducing the need for duplication and making the code easier to maintain. 4. What is type erasure in Java Generics? Type erasure in Java Generics is the process by which generic type information is removed at compile-time, leaving only the raw type information. This means that at runtime, generic types are treated as their raw type, and all type parameter information is lost. For example, when the generic class List<T> is compiled, it is treated as if it were a raw type List, without any information about the type parameter T. This allows Java Generics to maintain backwards compatibility with older versions of the Java language, as generic type information is not available at runtime. However, it also means that some type information is lost, and certain operations, such as reflection, may not work as expected with generic types..

[Audio] To create a generic class in Java, you must declare a type parameter in angle brackets after the class name. For instance, MyClass Object = new MyClass();. This indicates that the class MyClass can operate with objects of type Integer. Similarly, you can create a generic method by declaring a type parameter within angle brackets before the return type of the method. For example, public static void myMethod(T parameter) . This method can function with objects of any type. Wildcards in Java Generics are employed to specify unknown or generic types in a more flexible manner. There are two types of wildcards in Java Generics: upper bounded wildcards and lower bounded wildcards. Upper bounded wildcards are specified using the? symbol and the extends keyword. For instance, public void myMethod(List<? extends Number> list) . This specifies that the method myMethod accepts a List of any type that extends the Number class. Lower bounded wildcards are specified using the? symbol and the super keyword. For example, public void myMethod(List<? super Integer> list) . This specifies that the method myMethod accepts a List of any type that is a superclass of Integer..

[Audio] There are two types of wildcards in Java Generics: upper bounded wildcards and lower bounded wildcards. Upper bounded wildcards are specified using the '?' symbol and the 'extends' keyword. For example, 'List<? extends Number>'. This specifies that the list can hold elements of type 'Number' or any subtype of 'Number'. Lower bounded wildcards are specified using the '?' symbol and the'super' keyword. For example, 'List<? super Integer>'. This specifies that the list can hold elements of type 'Integer' or any supertype of 'Integer'. Wildcards are useful in situations where you want to write generic code that can accept a wide range of types, but still maintain some type safety and constraints on the types that can be used..

[Audio] A generic constructor in Java is created in the same way as a generic class or method. The constructor's type parameters are declared in angle brackets '<>' before the constructor's name, just like a generic class or method. An example of a generic class with a generic constructor is shown below: class MyClass //... } Note that the use of type casts in a generic constructor can lead to runtime errors if the cast is invalid. It is crucial to verify that the type argument is suitable and the cast will succeed. Generally, it is advisable to employ type bounds or other mechanisms to guarantee type safety when utilizing generic constructors..

[Audio] Java Generics enables you to specify multiple type parameters in a single declaration by separating them with commas within angle brackets. For instance, you can define a class with two type parameters like MyClass, indicating that the class has two type parameters, one for strings and another for integers. This allows you to specify the type of data that can be stored in the class, making it useful when creating a class that can work with different types of data without requiring separate classes for each type. Additionally, Java Generics permits overloading generic methods, enabling you to define multiple methods with the same name but different parameter lists. This is beneficial when creating a method that can work with diverse types of data without necessitating separate methods for each type. For example, you could define a method called genericMethod that takes a single type parameter and then overload it with a second version that takes a different type parameter, allowing you to invoke the method with various types of data without needing distinct methods for each type..

[Audio] Arrays are always of fixed size, i.e., a user can not increase or decrease the length of the array according to their requirement or at runtime, but In Collection, size can be changed dynamically as per need..

[Audio] The Java Collections Framework offers three primary interfaces: Set, Queue, and Map. The Set interface specifies a collection of distinct elements, while the Queue interface defines a data structure that stores elements in a First-In-First-Out manner. Additionally, the Map interface outlines a data structure that holds key-value pairs..

[Audio] The Iterator can traverse both legacy and non-legacy elements. Enumeration can only traverse legacy elements. The Iterator is fail-fast, meaning if the underlying collection changes during iteration, the Iterator will throw a ConcurrentModificationException. In contrast, Enumeration is not fail-fast. The Iterator is generally slower than Enumeration because it performs additional checks to ensure thread-safety. Enumeration, being a legacy interface, is faster than Iterator. Additionally, the Iterator can perform remove operations while traversing the collection, whereas Enumeration can only perform traversal operations..

[Audio] HashSet implements the Set interface, whereas HashMap implements the Map interface. Unlike HashSet, HashMap can contain duplicate values with unique keys. Additionally, while HashSet contains only a single null value, HashMap can hold a single null key with multiple null values. These differences underscore the distinct characteristics of each data structure, allowing developers to select the most appropriate choice based on their specific needs..

[Audio] =====. Lambda Expressions Syntax: (Argument List)-> or (Argument List)-> Example of Lambda Expression in Java: LambdaExpressionExample.java: public class LambdaExpressionExample }).start(); } } 23. What do you mean by Functional Interfaces in Java?.

[Audio] Java Generics allow us to define classes, interfaces, and methods that can work with objects of various types while providing compile-time type checking. This ensures that our code is robust, flexible, and easy to maintain. We can write reusable code that can handle different types of data, making our programs more efficient and scalable. For instance, we can create a generic class that can store and manipulate different types of data, such as integers, strings, or custom objects. This approach eliminates the need for explicit casting and reduces the risk of runtime errors. Furthermore, Generics facilitate better code organization and separation of concerns, enabling us to write more modular and maintainable software systems..