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Questions and Answers
What is the benefit of using a generic class like Genclass < T >?
Type safety and flexibility
What is the primary purpose of using generics in Java?
Code reusability
What would happen if we uncomment the line m.add("vivek"); in the First class?
Compile-time error
What is the purpose of the Display method in the First class?
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What is the advantage of using a generic method like Display?
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What is the output of the main method in the First class?
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Why is generics important in Java?
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What is the purpose of the type parameter E in the Display method?
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Can we use a generic method like Display with an array of objects?
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What is the benefit of using generics in a method like Display?
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Study Notes
Fixed Size and Its Limitations
- A fixed size has limitations, such as storing only homogeneous data and having no underlying data structures or built-in methods.
- These limitations can be overcome by using collections.
Java Collection
- Definition: A Java collection is a group of individual objects represented as a single unit.
- Framework: Java Collection provides an architecture to store and manipulate groups of objects.
- Advantages:
- Variable size or dynamic size
- Can store homogeneous and heterogeneous data
- Underlying data structures available, providing built-in methods
Collection Framework Hierarchy
- Key interfaces:
- Collection: The root of the collection hierarchy
- Set: A collection that cannot contain duplicate elements
- List: An ordered collection that can contain duplicate elements
- Queue: A collection used to hold multiple elements prior to processing
- Classes:
- ArrayList
- Vector
- LinkedList
- PriorityQueue
- HashSet
- LinkedHashSet
- TreeSet
Type Parameters
- Naming conventions for type parameters:
- T: Type
- E: Element
- K: Key
- N: Number
- V: Value
- Example: Using E to denote the element
Generic Method
- Definition: A generic method that can accept any type of arguments
- Scope: Limited to the method where it is declared
- Allows static and non-static methods
- Example: Printing array elements using a generic method
Generic Class with Multiple Parameters
- Definition: A generic class that can contain more than one parameter
- Syntax: ``
- Example: Creating a generic class with two parameters
Methods in Java Map Interface
- clear(): Clears and removes all elements from a specified map collection
- containsKey(Object): Checks if a particular key is mapped in the map
- containsValue(Object): Checks if a particular value is mapped by any of the keys in the map
- get(Key): Retrieves the value mapped by a particular key
- hashCode(): Generates a hashCode for the given map
- isEmpty(): Checks if a map is having any entry for key and value pairs
- put(Object, Object): Associates the specified value with the specified key in the map
- putAll(Map): Copies all mappings from the specified map to this map
- remove(Object): Removes the mapping for a key from this map
- size(): Returns the number of key-value pairs in the map
Wildcard
- Definition: A special character (?) used to represent an unknown type parameter
- Types of wildcards:
- Upper Bounded Wildcard (?extends T): Specifies that the wildcard can be substituted with any type that is a subtype of T
- Lower Bounded Wildcard (?super T): Specifies that the wildcard can be substituted with any type that is a supertype of T
Example Programs
- Example 1: Generic class
- Example 2: Generic method (using foreach loop to traverse elements)
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Description
This quiz covers the basics of collections in Java programming, including fixed size, homogeneous data, and overcoming limitations with collections.
