OCP Exam Preparation.

Contents at a Glance.

• Oracle Documentations
• About
• Enum
• InstanceOf
• Nested Class
• Methods from Object Class
• Imports
• Casting Values
• Java Inheritance
• Polymorphism
• Referenceable Objects and References
• Design Principles
• Design Pattern
• Functional Interface
• Lambda Expression
• Method Reference
• Generics
• Collections
• Array
• Arrays
• Stream API
• Help
• License

Oracle Documentations.

• Exam Java SE 8 Programmer II
• Java® Language Specification. Java SE 8 Edition
• Java Platform, Standard Edition (Java SE) 8
• Java™ Platform, Standard Edition 8 API Specification

About.

• This project created for educational purposes, and this project may contain invalid or false "Information or Cod Examples".
  
• Always check the "Information or Cod Examples" you are learning.
  

Enum.

Initialization.

• 1.

Semicolon.

• 1.
• 2.
• 3.

Constructor.

Access Modifier.

• Enum constructor must have access modifier private or package.

Inheritance.

• Inheritance not allowed for "Enum". It is only allowed to implement the interface.

Using "Switch" with "Enum".

• Work with "Enum" and with "Switch".

Values.

• Values of Enum.

Constructors.

Methods.

Access Modifier.

Abstract.

• Implementation abstract method in each "Enum Value".
• Each and every "Enum Value", required to implement this abstract method.
• If "Enum Value", have implemented method, "Enum" required to have defined this abstract method, so that later this method could be called.
• Is allowed implementation many abstract method in "Enum Values".

Non-static.

• Implementation this method in each "Enum Value".
• Is not mandatory implementing methods in every "Enum Values".
• If "Enum Value", have implemented method, "Enum" required to have defined this method, so that later this method could be called.
• Is allowed implementing many methods in "Enum Values".

Static.

Final.

Variables.

Access Modifier.

Non-static.

Static

Final

Methods.

Pre-defined Methods.

• Work with "Enum" method "valueOf".
• Work with "Enum" method "values".
• Work with "Enum" method "ordinal".

Access Modifier.

Abstract

Non-static.

Static

• Is allowed definition many static methods in "Enum".
• Is not allowed implementing static methods in "Enum" values.

Final

Variables.

Access Modifier.

Non-static.

Static

Final

Note to self.

Nested Class.

• Exist two types of classes: top-level class, Nested Class.
  
• Nested Class divided into two types: "Static Nested Class" and "Inner Class".
  
• Sywchestvyet "Anonymous class". "Anonymous class" siempre is "Nested Class" no potom stanovitca libo "Static Nested Class" libo "Inner Class".
  
• "Nested Class" may have "access modifier": private, default, protected, public.
  

Static Nested Class.

Type of Static Nested Class

• Exist four types of Static Nested Class: interface, abstract class, class, enum.
  

Inheritance.

Initialization of "Static Nested Class".

• 1.
• 2.

Access Modifier of "Static Nested Class".

Constructors.

Access Modifier.

Variables.

Access Modifier.

Non-static.

• Non-static variables from "top-level class" cannot be used in the "static nested class".
  

Static.

• Static variables from "top-level class" can be used in the "static nested class".
  

Final.

Methods.

Access Modifier.

Abstract.

Non-static.

• Not allowed definition "static nested class" in the method body.
  

Static.

• Not allowed definition "static nested class" in the static method body.
  

Final.

Note to self.

• Null Reference.

Local Static Nested Class.

• The definition for the "Local Static Nested Class" is not allowed.

Inner Class.

• The "Inner Class" has a subtype that name is "Local Inner Class".
  
• Ekzempliar "Inner Class" vsehda dolzen sodirzat ssulky na "top-level class".
  
• Esli sozdaietsa "top-level class" eto ne znachit chto proisxodit sozdanie "Inner Class".
  
• Esli sozdaietsa "Inner Class" to obiazan sywchestvovat ekzempliar "top-level class". I "Inner Class" bydet ssulatsa na "top-level class".
  
• Raznue "Inner Class" mohut ssulatsa na odin i totze "top-level class".
  
• "Inner Class" mozet bit obiavlion v methode. No znachenie kotoroe vozvrawchaet ethot method ne mozet bit tipos etoho "Inner Class". "Inner Class" kotorui obiavlaetsa v nytri methoda, ne viden za figurnumi scobcami etoho methoda. Znachenie cotoroe vozvrawchaet method mozet bit "Object type" i takim sposobom mozno vozvrawcaht "Inner Class" kororui opredelon v methode.
• java memory leak. "Inner Class" mozet sprovocurovat "java memory leak". Do toho vremeni kohda ziv "Inner Class" bydet ziv "top-level calss", "Garbage Collector" ne smozet ydalit "top-level class".
  

Type of Inner Class

• Exist four types of Inner Class: interface, abstract class, class, enum.
  

Inheritance.

Initialization of "Inner Class".

• 1.
• 2.

Access Modifier of "Inner Class".

• If "Inner Class" have "access modifier" private, then this "Inner Class" may have methods with any "access modifier".
• If "Inner Class" have "access modifier" private, then this "Inner Class" may have variables with any "access modifier".

Constructors.

Access Modifier.

Variables.

Access Modifier.

Non-static.

• Non-static variables from top-level class can be used in the inner class.
• Non-static variables can be use in "Inner Class".

Static.

• Static variables from top-level class can be used in the inner class.
• Static variables is not allowed define in "Inner Class".

Final.

Methods.

Access Modifier.

Abstract.

Non-static.

• Non-static methods from top-level class can be used in the inner class.
• Non-static methods can be used in the "Inner Class".

Static.

• Static methods from top-level class can be used in the inner class.
• Static methods is not allow use in "Inner Class".

Final.

Note to self.

• Null Reference.

Local Inner Class.

• The definition for the "Local Inner Class".
• Local Inner Class can't have an access modifier.
• Local Inner Class can't be declared static.
• Local Inner Class have access to local variables without access modifier and final local variables of the method.

Type of Local Inner Class

Inheritance.

Access Modifier of "Local Inner Class".

Constructors.

Access Modifier.

Variables.

• Local Inner Class have access to all variables of the outer class.

Access Modifier.

Non-static.

Static.

• Local Inner Class can't have an variables static.

Final.

Methods.

• Local Inner Class have access to all methods of the outer class.

Access Modifier.

Abstract.

Non-static.

Static.

• Local Inner Class can't have an methods static.

Final.

Note to self.

Anonymous Class.

• If type of an "Anonymous Class" is "Abstract Class". And this "Abstract Class" have "abstract methods", all "abstract methods" from this "Abstract Class" is mandatory must be defined.
• If type of an "Anonymous Class" is "Interface". And this "Interface" have "abstract methods", all "abstract method" from this "Interface" is mandatory must be defined.
• Type of an "Anonymous Class" is "Static Nested Class".
• Type of an "Anonymous Class" is "Inner Class".

Initialization.

• Initialization of "Anonymous Class".

Final Class.

• An type of an "Anonymous Class" cannot be final.

Methods.

• If some type of an "Anonymous Class" have "final method" and you want implement this "final method", that will be impossible. It is not allowed to redefine final methods.
• If some type of an "Anonymous Class" have "static method" and you want implement this "static method", that will be impossible. It is not allowed to redefine static methods.
• Private methods are not allowed to redefine. Methods of access modifier: public, protected, package is allowed redefine, considering the relationship policy of "Access Modifiers".

Variables.

• Access to variables of an "Anonymous Class".
• Access to variables of an "Anonymous Class" using "this".
• Access to final variables of an "Anonymous Class".
• The final variables from the "Anonymous Class" cannot be changed.
• Access to static variables of an "Anonymous Class".
• The final variables from the "Anonymous Class" can be changed.
• Private variables are not allowed to redefine. Variables of access modifier: public, protected, package is allowed redefine, considering the relationship policy of "Access Modifiers".

Methods from Object class.

equals.

• Difference between "getClass()" and "instanceof"
• Difference between "getClass()" and "instanceof"

hashCode.

toString.

getClass.

• 1.

clone.

Imports.

Static Import.

• Example of correct definition of "Static Import".

Casting Values.

• If casting operation is incorrect while be throw "Runtime Exception".
• Here are some basic rules to keep in mind when casting variables:
  
  • Casting an object from a subclass to a superclass doesn’t require an explicit cast.
    
  • Casting an object from a superclass to a subclass requires an explicit cast.
    
  • The compiler will not allow casts to unrelated types.
    
  • Even when the code compiles without issue, an exception may be thrown at runtime if the object being cast is not actually an instance of that class.

Explicit Cast.

Without an Explicit Cast.

Java Inheritance.

• Virtual Methods in object-oriented programming, a virtual function or virtual method is a function or method whose behaviour can be overridden within an inheriting class by a function with the same signature to provide the polymorphic behavior.

Class.

• "Class" can only be "extend" from one "class" or one "abstract class".
• "Class" can be "implement" may "interfaces".
• If the "Class is final", other class cannot be inherited from it.

Constructor.

Access Modifier.

• If class have only defined "private constructor", other class cannot be inherited from it. By marking the constructors private, we have implicitly marked the class final.

Variables.

• Class variables are not inherited.

Methods. In other words "Overriding".

• Method Inheritance.

Access Modifiers.

Abstract Methods.

Final Methods.

Non-static Methods.

Static Methods.

Interface.

• "Interface" can be "extend" from many others "interfaces".
• "Interface" cannot be "extend" from "class" or "abstract class".
• "Marker Interface" - this is an "interface" that has no methods.
• Interfaces cannot extend classes, nor can classes extend interfaces.
• Interfaces may also not be marked final or instantiated directly.
• There are additional rules for default methods, such as Java failing to compile if a class or interface inherits two default methods with the same signature and doesn’t provide its own implementation.

Variables.

• The compiler automatically adds "public static final" to all interface variables, if the developer does not provide them.
• Only "public static final" variables are allowed define in the "Interface". All variables from "Interface" is "public static final".

Access Modifier.

• Only "public" variables are allowed define in the "Interface". All variables from "Interface" have "public access modifier".

Static.

• Only "static" variables are allowed define in the "Interface". All variables from "Interface" is "static".

Final.

• Only "final" variables are allowed define in the "Interface". All variables from "Interface" is "final".

Methods. In other words "Overriding".

• The compiler automatically adds "public abstract" to all non‐static and non‐default methods, if the developer does not provide them.

Access Modifiers.

• Only public methods can be defined in a interface.

Abstract Methods.

Default Methods.

Static Methods.

Abstract Class.

• "Abstract Class" can only be "extend" from one "class" or one "abstract class".
• "Abstract Class" can be "implement" many "interfaces".

Variables.

Methods. In other words "Overriding".

Access Modifiers.

Abstract Methods.

Final Methods.

Non-static Methods.

Static Methods.

Polymorphism.

• The dictionary definition of polymorphism refers to a principle in biology in which an organism or species can have many different forms or stages. This principle can also be applied to object-oriented programming and languages like the Java language. Subclasses of a class can define their own unique behaviors and yet share some of the same functionality of the parent class.
  
• Polymorphism is the ability of a single interface to support multiple underlying forms. In Java, this allows multiple types of objects to be passed to a single method or class. In Java, this allows multiple types of objects to be passed to a single method or class.
  
• Types of Polymorphism:
  
  • Inheritance.
    
  • Generics.
    
  • 
    
  • 
    

Referenceable Objects and References.

• We can summarize this principle with the following two rules:
  
  • The type of the object determines which properties exist within the object in memory.
    
  • The type of the reference to the object determines which methods and variables are accessible to the Java program.
    
• An object is an instance of a class created from it using the new keyword.
  
• Classes, interfaces, arrays, enumerations and, annotations are the in Java are reference types in Java. Reference variables hold the objects/values of reference types in Java.
  

InstanceOf.

• Example of "InstanceOf".
• Example of "null instanceOf someValue".

Design Principles.

• A design principle is an established idea or best practice that facilitates the software design process.
  
• In general, following good design principles leads to:
  • More logical code
  • Code that is easier to understand
  • Classes that are easier to reuse in other relationships and applications
  • Code that is easier to maintain and that adapts more readily to changes in the application requirements

Encapsulating Data.

• Incorrect definition of "Encapsulation Data".
• Correct definition of "Encapsulation Data".

Creating JavaBeans.

• JavaBeans Spec URL

• JavaBean naming conventions:
  1. Properties are private.
  2. A public no-argument constructor.
  3. Getter for non‐boolean properties begins with "get".
  4. Getters for boolean properties must begin with "is".
  5. Getters for Boolean properties must begin with "get".
  6. Setter methods begin with "set".
  7. The method name must have a prefix of "set", "get", "is" followed by the first letter of the property in uppercase and followed by the rest of the property name.
  8. Implements Serializable.
  

• Although boolean values use "is" to start their getter method, the same does not apply to instances of the wrapper Boolean class, which use "get".
  

• Example of Java Bean.

Is‐a Relationship.

Has‐a Relationship.

Composing Objects.

Delegation.

Design Pattern.

• A design pattern is an established general solution to a commonly occurring software development problem. The purpose of a design pattern is to leverage the wealth of knowledge of developers who have come before you in order to solve old problems that you may encounter easily. It also gives developers a common vocabulary in which they can discuss common problems and solutions.

Singleton Pattern.

Lazy Initialization.

Thread Safe.

Singleton and Class Loader.

Immutable Objects.

1. Use a constructor to set all properties of the object.
   
2. Mark all of the instance variables private and final.
   
3. Don’t define any setter methods.
   
4. Don’t allow referenced mutable objects to be modified or accessed directly.
   
5. Prevent methods from being overridden.
   

Builder Pattern.

Factory Pattern.

Factory Method Pattern.

Functional Interface.

• "Functional Interface" as an "Interface" that contains a single "Abstract Method". Bat may have defined "Default Method" or "Static Method". Or may have defined both methods at the same time.

Lambda Expression.

Parameters of Lambda.

• The parentheses can be omitted in a lambda expression if there is exactly one input parameter and the type is not explicitly stated in the expression. This means that expressions that have zero or more than one input parameter will still require parentheses.
• Pass one parameter to "Lambda Expression".
• Pass two or many parameters to "Lambda Expression".

Body of Lambda.

• Semicolon.
• Return Value.
• Since Java doesn’t allow us to re-declare a local variable.

Method Reference.

Generics.

• Oracle Java Documentation. The Java Generic Tutorials.
• Covariant, Contravariance, Invariance.
• Oracle Java Documentation. Lower Bounded Wildcards.
• Oracle Java Documentation. Upper Bounded Wildcards.
• 1.

Unbounded wildcard.

• Initialization.
• Constructor.
• Method Parameter.
• Method Return Value.
• Definition Interface.
• Definition Abstract Class.
• Definition Class.
• Definition Enum.

Lower Bounded Wildcards.

• Initialization.
• Constructor.
• ? super OneType & OtherType.
• Method Parameter.
• Method Return Value.
• Definition Interface.
• Definition Abstract Class.
• Definition Class.
• Definition Enum.

Upper Bounded Wildcards.

• Initialization.
• Constructor.
• ? extends OneType & OtherType.
• Method Parameter.
• Method Return Value.
• Definition Interface.
• Definition Abstract Class.
• Definition Class.
• Definition Enum.

Generic Classes.

Generic Nested Classes.

Generic Abstract Class.

Generic Interface.

Generic Function Interface.

Generic Constructor.

Generic Methods.

• 1.
• Type of Parameters.
• Return Value.

Collections.

• For any type of collections, the methods is very important: equals, hashCode, compare, compareTo.

Big O, Big Theta, Big Omega.

Big-O.

Big-Theta.

Big-Omega.

Collections Utils Class.

Methods.

• sort()

• binarySearch()

Iterable.

List.

• A list is an ordered collection of elements that allows duplicate entries. Elements in a list can be accessed by an int index.

ArrayList.

Constructor.

• ArrayList<>()
• ArrayList<>(int initialCapacity)
• ArrayList<>(java.util.Collection<? extends E> c)

Methods.

add

• boolean add (E element)
• void add (int index, E element)

set

• E set (int index, E element)

get

• E get (int index)

remove

• E remove (int index)
• boolean remove(Object o)

isEmpty

size

clear

contains

• This method calls equals() on each element of the ArrayList to see if there are any matches.

indexOf

lastIndexOf

iterator

Initialization.

LinkedList.

• A LinkedList implements List and Queue.
  

Old Collections.

Vector.

Stack.

• If you need a stack, use an ArrayDeque instead
  

Set.

• A set is a collection that does not allow duplicate entries.

HashSet

• A HashSet stores its elements in a hash table. This means that it uses the hashCode() method of the objects to retrieve them more efficiently.
  
• The equals() method is used to determine equality.
  

Constructor.

• HashSet<>()
• HashSet<>(int initialCapacity)
• HashSet<>(java.util.Collection<? extends E> c)
• HashSet<>(int initialCapacity, float loadFactor)

Methods.

add

• boolean add(E e)

remove

• boolean remove(Object o)

isEmpty

size

clear

contains

• This method calls equals() on each element of the HashSet to see if there are any matches.

Initialization.

LinkedHashSet.

TreeSet.

• A TreeSet stores its elements in a sorted tree structure. The main benefit is that the set is always in sorted order.
• TreeSet implements the NavigableSet interface. And the interface NavigableSet implemented SortedSet. And the interface SortedSet implemented Set.

Constructor.

• TreeSet<>()
• TreeSet(Collection<? extends E> c)
• TreeSet(Comparator<? super E> comparator)
• TreeSet(SortedSet s)

Methods.

add

• boolean add (E e)

remove

• boolean remove (Object o)

isEmpty

• boolean isEmpty ()

size

• int size ()

clear

• void clear ()

contains

• boolean contains(Object o)
• This method calls equals() on each element of the TreeSet to see if there are any matches.

lower

• E lower (E e)

floor

• E floor (E e)

ceiling

• E ceiling (E e)

higher

• E higher (E e)

Map.

• A map is a collection that maps keys to values, with no duplicate keys allowed. The elements in a map are key/value pairs.

Queue.

• You use a queue when elements are added and removed in a specific order. Queues are typically used for sorting elements prior to processing them.
  
• A queue is a collection that orders its elements in a specific order for processing. A typical queue processes its elements in a FIFO (first-in, first-out) order, but other orderings are possible.

PriorityQueue.

Constructor.

• PriorityQueue()
• PriorityQueue(Collection<? extends E> c)
• PriorityQueue(Comparator<? super E> comparator)
• PriorityQueue(int initialCapacity)
• PriorityQueue(int initialCapacity, Comparator<? super E> comparator)
• PriorityQueue(PriorityQueue<? extends E> c)
• PriorityQueue(SortedSet<? extends E> c)

Methods.

add

• boolean add (E e)

remove

• boolean remove (Object o)

isEmpty

• boolean isEmpty ()

size

• int size ()

clear

• void clear ()

contains

• boolean contains(Object o)
• This method calls equals() on each element of the TreeSet to see if there are any matches.

ArrayDeque.

Constructor.

• ArrayDeque<>()
• ArrayDeque(Collection<? extends E> c)
• ArrayDeque(int numElements)

Methods.

add

• boolean add (E e)

remove

• E remove ()
• boolean remove (Object o)

isEmpty

• boolean isEmpty ()

size

• int size ()

clear

• void clear ()

contains

• boolean contains(Object o)
• This method calls equals() on each element of the TreeSet to see if there are any matches.

Heap.

Additional Information.

Method "equals()".

• 1.

Method "hashCode().

Interfaces "Comparable" and "Comparator". Methods compareTo() and compare().

Concurrent Collections.

Array.

• 1.

Arrays.

• asList()
• sort()
• parallelSort()
• binarySearch()

Stream API.

Compiler.

• Compiler Warning is different from a compiler error in that all of the code still compiles with a compiler error. The compiler warning is Java informing you that you should take a closer look at something.

Help

License

Apache 2.0, see LICENSE.