CS计算机代考程序代写 compiler Java algorithm COMP2511

程序代写 CS代考 / Algorithm算法代写代考, compiler, Java代写代考

COMP2511

Generics and Collections in Java

Prepared by

Dr. Ashesh Mahidadia

Generics in Java
(Part 1)

2COMP2511: Generics and Collections in Java

Generics in Java
Generics enable types (classes and interfaces) to be parameters when defining:

• classes,
• interfaces and
• methods.

Benefits
v Removes casting and offers stronger type checks at compile time.
v Allows implementations of generic algorithms, that work on collections of different types, can

be customized, and are type safe.
v Adds stability to your code by making more of your bugs detectable at compile time.

COMP2511: Generics and Collections in Java 3

Without Generics With Generics

Generic Types

v A generic type is a generic class or interface that is parameterized over types.

v A generic class is defined with the following format:
class name< T1, T2, ..., Tn > { /* … */ }

v The most commonly used type parameter names are:
v E – Element (used extensively by the Java Collections Framework)
v K – Key
v N – Number
v T – Type
v V – Value
v S,U,V etc. – 2nd, 3rd, 4th types

v For example,
Box integerBox = new Box();

OR
Box integerBox = new Box<>();

COMP2511: Generics and Collections in Java 4

Multiple Type Parameters

v A generic class can have multiple type
parameters.

v For example, the generic OrderedPair class,
which implements the generic Pair interface

COMP2511: Generics and Collections in Java 5

v Usage examples,

Pair p1 = new OrderedPair(“Even”, 8);
Pair p2 = new OrderedPair(“hello”, “world”);
… …
OrderedPair p1 = new OrderedPair<>(“Even”, 8);
OrderedPair p2 = new OrderedPair<>(“hello”, “world”);
… …
OrderedPair> p = new OrderedPair<>(“primes”, new Box(…));

Generic Methods
Generic methods are methods that introduce their own type parameters.

COMP2511: Generics and Collections in Java 6

The complete syntax for invoking this method would be:

Pair p1 = new Pair<>(1, “apple”);
Pair p2 = new Pair<>(2, “pear”);
boolean same = Util.compare(p1, p2);

The type has been explicitly provided, as shown above.
Generally, this can be left out and the compiler will infer the type that is needed:

Pair p1 = new Pair<>(1, “apple”);
Pair p2 = new Pair<>(2, “pear”);
boolean same = Util.compare(p1, p2);

Collections in Java

COMP2511: Generics and Collections in Java 7

Collections in Java
A collections framework is a unified architecture for representing and manipulating
collections. A collection is simply an object that groups multiple elements into a single unit.

All collections frameworks contain the following:

v Interfaces: allows collections to be manipulated independently of the details of their
representation.

v Implementations: concrete implementations of the collection interfaces.

v Algorithms: the methods that perform useful computations, such as searching and
sorting, on objects that implement collection interfaces.
• The algorithms are said to be polymorphic: that is, the same method can be used

on many different implementations of the appropriate collection interface.

COMP2511: Generics and Collections in Java 8

Core Collection Interfaces:
v The core collection interfaces encapsulate different types of collections

v The interfaces allow collections to be manipulated independently of the details of their
representation.

COMP2511: Generics and Collections in Java 9

The Collection Interface

v A Collection represents a group of objects known as its elements.
v The Collection interface is used to pass around collections of objects where maximum

generality is desired.
v For example, by convention all general-purpose collection implementations have a

constructor that takes a Collection argument.
v The Collection interface contains methods that perform basic operations, such as

• int size(),
• boolean isEmpty(),
• boolean contains(Object element),
• boolean add(E element),
• boolean remove(Object element),
• Iterator iterator(),
• … …many more …

More at : https://docs.oracle.com/javase/tutorial/collections/interfaces/collection.html

COMP2511: Generics and Collections in Java 10

https://docs.oracle.com/javase/tutorial/collections/interfaces/collection.html

Collection Implementations

v The general purpose implementations are summarized in the following table:

COMP2511: Generics and Collections in Java 11

Interface Hash Table Resizable Array Balanced Tree Linked List Hash Table + Linked List
Set HashSet TreeSet LinkedHashSet
List ArrayList LinkedList

Deque ArrayDeque LinkedList
Map HashMap TreeMap LinkedHashMap

Implemented Classes in the Java Collection,
Read their APIs.

v Overview of the Collections Framework at the following page:

https://docs.oracle.com/javase/8/docs/technotes/guides/collections/overview.html

https://docs.oracle.com/javase/8/docs/api/java/util/HashSet.html
https://docs.oracle.com/javase/8/docs/api/java/util/TreeSet.html
https://docs.oracle.com/javase/8/docs/api/java/util/LinkedHashSet.html
https://docs.oracle.com/javase/8/docs/api/java/util/ArrayList.html
https://docs.oracle.com/javase/8/docs/api/java/util/LinkedList.html
https://docs.oracle.com/javase/8/docs/api/java/util/ArrayDeque.html
https://docs.oracle.com/javase/8/docs/api/java/util/LinkedList.html
https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html
https://docs.oracle.com/javase/8/docs/api/java/util/TreeMap.html
https://docs.oracle.com/javase/8/docs/api/java/util/LinkedHashMap.html
https://docs.oracle.com/javase/8/docs/technotes/guides/collections/overview.html

Wrappers for the Collection classes

• https://docs.oracle.com/javase/tutorial/collections/implementations/
wrapper.html

COMP2511: Generics and Collections in Java 12

https://docs.oracle.com/javase/tutorial/collections/implementations/wrapper.html

Demo: Collections Framework

Demo …

COMP2511: Generics and Collections in Java 13

End

COMP2511: Generics and Collections in Java 14

Related Posts