JAVA FULL STACK
DEVELOPMENT PROGRAM
Java SE Collection
OUTLINE
• Collection
• Map
• Ordering
• Java 8
HIERARCHY
COLLECTION
• Group of objects
• It is not speci ed whether they are
• Ordered / not ordered
• Duplicated / not duplicated
• Following constructors are common to all classes implementing Collection
• T()
• T(Collection c)
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COLLECTION
LIST
• Can contain duplicate elements
• Homogeneous
• Insertion order is preserved
• User can de ne insertion point
• Elements can be accessed by position
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LIST ADDITIONAL METHOD
LIST IMPLEMENTATION
[1,2,3,4,5] 1->2->3->4->5
[1,3,4,5] 1->3->4->5
QUEUE
• Collection whose elements have an order
• FIFO: First In First Out
• De nes a head position where is the rst element that can be
accessed
• offer()
• peek()
• poll()
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QUEUE IMPLEMENTATION
• LinkedList
• PriorityQueue
SET
• Contains no methods other than those inherited
from Collection
• add() has restriction that no duplicate elements
are allowed
SET IMPLEMENTATION
• HashSet
• Insertion order is not preserved
• LinkedHashSet
• Insertion order is preserved
•
OUTLINE
• Collection
• Map
• Ordering
• Java 8
HIERARCHY
MAP
• An object that associates keys to values
• Keys and values must be objects(Wrapper Class)
• Keys must be unique
• Only one value per key
MAP INTERFACE
MAP
EQUALS(). ==
• ==
• Address comparison
• If point to the same memory location
• Equals:
• Values in the object
EQUALS()
• It is re exive: x.equals(x) == true
• It is symmetric: x.equals(y) == y.equals(x)
• It is transitive: for any reference values x, y, and z, if x.equals(y) == true
AND y.equals(z) == true => x.equals(z) == true
• It is consistent: for any reference values x and y, multiple invocations of
x.equals(y) consistently return true (or false), provided that no
information used in equals comparisons on the object is modi ed.
• x.equals(null) == false
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HASHCODE()
• Return Type: int
• Object.hashCode()
HASHCODE()
• The hashCode() method must consistently return the same int, if information
used in equals() to compare the objects is not modi ed.
• The hashCode contract in Java 8:
• If two objects are equal for equals() method, then calling the hashCode()
method on the two objects must produce the same integer result.
• If two objects are unequal for equals() method, then calling the hashCode()
method on the two objects MAY produce distinct integer results.
• Producing distinct int results for unequal objects may improve the
performance of hashmap
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MAP
• Get/set takes constant time (in case of no collisions)
• Implementations
• HashMap implements Map
• LinkedHashMap extends HashMap
• TreeMap implements SortedMap
SORTED MAP
OUTLINE
• Collection
• Map
• Ordering
• Java 8
OBJECT ODERRING
• How to sort collections
• Bubble sort
• Selection sort
• Quick sort
• Merge sort
• Take the advantage of Collection
COLLECTIONS
• Static methods of java.util.Collections class
• sort() - Tim sort, n log(n)
• binarySearch() – requires ordered sequence
• reverse() - requires ordered sequence
• min(), max() – in a Collection
DEFAULT IMPLEMENTATION
• The interface is implemented by language common
types in packages java.lang and java.util
• String objects are lexicographically ordered
• Date objects are chronologically ordered
• Number and sub-classes are ordered numerically
CUSTOM ORDERING
• Comparable<T> interface
• Comparator<T> interface
COMPARABLE INTERFACE
• Compares the receiving object with the speci ed object
• Return value must be:
• <0, if this precedes obj
• ==0, if this has the same order as obj
• >0, if this follows obj
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COMPARATOR INTERFACE
• Compares its two arguments
• Return value must be
• <0, if o1 precedes o2
• ==0, if o1 has the same ordering as o2
• >0, if o1 follows o2
OUTLINE
• Collection
• Map
• Ordering
• Java 8
JAVA 8 NEW FEATURES
• Lambda Expression
• Functional Interface
LAMBDA EXPRESSION
• Simpli es development
• Before Java 8, there is anonymous class
• Syntax
• parameter -> expression
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FUNCTIONAL INTERFACES
FUNCTIONAL INTERFACE
• Interface that contains ONLY ONE abstract
method
• Comparator is a functional interface
LAMBDA EXPRESSION
+
FUNCTIONAL INTERFACE
• Lambda Expression and Functional Interface works
together to simplify code
CONSUMER INTERFACE
• Consumer is a functional interface which
represents an operation that accepts a single
input argument and returns no result
• Methods:
• accept()
• andThen()
SUPPLIER INTERFACE
• Supplier is a functional interface which
represents an operation that takes no argument
and returns a result
• Methods:
• get()
FUNCTION INTERFACE
• Function is a functional interface which represents an
operation that takes an argument and returns a result
• The argument and result can be different types
• Methods:
• apply()
• andThen()
• compose()
• identity()
PREDICATE INTERFACE
• Predicate is a functional interface which
represents an operation that takes an argument
and returns a boolean result
• Methods:
• test()
• and()
• or()
• negate()
QUESTIONS?
