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Abstraction

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Java

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Date created

Mar 1, 2020

Cards (50)

Section 1

(50 cards)

Abstraction

Front

Is the methodology of hiding the implementation details from the user and only providing the functionality to the users

Back

Why Java is platform independent?

Front

means once compiled you can execute the program on any platform(OS) The compiler converts the source code to bytecode, which is intermidiate Language, Bytcode can be executed on any platform using JVM

Back

Polymorphism

Front

The ability of a variable, function or object to take multiple forms

Back

Methods

Front

Used to represent the behavior of the object Must have a return type Needs to invoked explicitly No default method is provided by the compiler Method name may or may not be same as class name

Back

Java

Front

Java is a programming language and computing platform first released by Sun Microsustems in 1995

Back

Why pointers are not used in Java?

Front

Java doesnt use pointers because they are unsafe and increases the complexity of the program

Back

What is OOP?

Front

Object Oriented Programming, OOP is a powerful way to approach the job of programming, and is the center of Java programming.

Back

Object (Java)

Front

An object is a real-world entity that has a state and behavior. An object has three characteristics State, Behavior and Identity is created using the 'new' key-word

Back

JRE

Front

(Java Runtime Environment) creates the JVM and ensures dependencies are available to your programs

Back

difference between stack memory and java heap

Front

1)Heap memory is used by all the parts of the application whereas stack memory is used only by one thread of execution 2) Whenever an object is created, its always stored in the heap space and stack memory contains the reference to it, stack memory only contais local primitive variables and reference variables to objects in heap space 3) Objects stored in the heap are globally accessible whereas stack memory cant't be accessed by other threads 4)memory management in stack is done in LIFO manner whereas its more complex in Heap memory because its used globally. Heap memory is divided into Young-Generation, Old-Generation. 5)Stack memory is short-lived whereas heap memory lives from the start till the end of the application execution 6)When stack memory is full java runtime throws java.lang.StackOverFlowError whereas if heap memory is full, it throws java.lang.OutOfMemoryError: Java Heap Space error 7)Stack memory size is very less when compared to Heap memory.

Back

Java Heap

Front

is used by java runtime to allocate memory to Objects and JRE classes Whenever we create any object, its always created in the heap space

Back

Public access Modifier

Front

Access is not restricted.

Back

protected access modifier

Front

Can not be used for classes and interfaces, it also cannot be used for fields and methods with in interface. Fields, methods and constructors declared protected in a superclass ca be accessed only by superclasses in other packages. Classes in the same package can also access protected fields methods and constructors as well, even if thy are not a subclass of the protected members class

Back

Eager Initialization

Front

The instance of Singleton Class is created at the time of class loading by making the constructor as private you are not allowing other class to create a new instance of the class you want to create the singleton. Instead you are creating one public static method(commonly name as for getInstance()) to provide the single entry point to create the new instance of the class.(this instance is created even though client application migh not be using it.

Back

wrapper class

Front

A class that contains a primitive type value, such as Integer.

Back

Java Platforms / Editions

Front

Java SE (Java Standard Edition), Java EE (Java Enterprise Edition), Java ME (Java Micro Edition), JavaFX

Back

non-static method

Front

No need to use the static keyword before the method name It is can be called like any general method It can access any static method and any static variable without creating an instance of the class

Back

Static methods

Front

Must be used before the method name It is called using the class they can not access any non-static instance variables or methods

Back

Abstraction vs Encapsulation

Front

1)Abstraction hides details at the design level and Encapsulation hide details at the implementation level 2)Abstraction is used for hiding the unwanted data and giving relevant data, Encapsulation means hiding the code and data into a single unit to protect the data from outside world 3)Abstraction lets you focus on what the objects does instead of how it does it and Encapsulation means hiding the internal details or mechanics of how an object does something.

Back

JVM

Front

(Java Virtual Machine) is the platform component that executes your programs

Back

What is the difference between a local variable and an instance variable?

Front

Local variable is tipically used inside a method constructor or block and has only local scope. Isntance variable is java is a variable which is bounded to its object itself. these variable are declared within a class. but outside a method. Every object of that class will create its own copy of the variable while using it.

Back

What is a Map in Java

Front

Map is an Interface of Util package which maps unique keys to values. The map interface is not a subset of the main Collection interface andthus it behaves little different from the other collection types. Map doesnt contain duplicate keys Each key can map at max one value

Back

Why java is not 100% Object-oriented?

Front

Java is not 100% Object-oriented because it makes use of eight primitive datatypes such as boolean, byte, char, int, float, double, long, short which are not objects.

Back

What is a singleton class in java

Front

Is a class that can have only one object(an instance of the class) at a time limiting the number of objects to only one.

Back

default access modifier

Front

Java provides a default specifier wich is used when no access modifier is present. Any class, field, method or constructor that has no declared access modifier is accessible only by classes in the same package. Is not used for fields and methods within an interface

Back

What is final keyword?

Front

final keyword is used with Class to make sure no other class can extend it, for example String class is final and we can't extend it. We can use final keyword with methods to make sure child classes can't override it. final keyword can be used with variables to make sure that it can be assigned only once. However the state of the variable can be changed, for example we can assign a final variable to an object only once but the object variables can change later on. Java interface variables are by default final and static.

Back

Main Method

Front

public static void main(String[] args) Every program need a place to start the execution. public - access modifier meaning global visibility static - the method can be accessed straight from the class, we dont have to instantiate an object to have a reference and use it void - means that this method doesnt return a value main - the name of the method, that is the identifier JVM looks for when executiong Java program the parameters args is an array of Strigns

Back

What are the main concepts of OOPs in Java?

Front

Inheritance, Encapsulation, Abstraction and Polymorphism

Back

Constructor

Front

Used to initialize the state of an object Do not have any return type Is invoke implicitly A defaul constructor is provided by the compiler if the class has none Constructor name must always be the same as the class name

Back

how can we make a singleton class

Front

Using eager Initialization or lazy initialization

Back

Java Stack Memory

Front

is used for execution of a thread. They contain method specific values that are short-lived and references to other objects in the heap that are getting referred from the method

Back

Type of Access Modifiers

Front

Default, Private, Protected, Public

Back

What is Java String Pool?

Front

Refers to a collection of Strings which are stored in the heap memory.

Back

Lazy Initialization

Front

Opposite to Eager initialization, here you are going to initialize new instance of the class in getInsstance() method it self. this method will check if there is any instance of that class is already created?

Back

Overloading

Front

is a feature that allows a class to have more than one method having the same name if their arguments list are different.

Back

what are constructors in java

Front

In Java, constructor refers to a block of code which is used to initialize an object. It must have the same name as that of the class. Also, it has no return type and it is automatically called when an object is created.

Back

JDK

Front

(Java Development Kit) allowa you to create Java programs that can be executed and run by the JVM and JRE

Back

Private Access Modifier

Front

fields or methods cannot be used for classes and onterfaces. it also cannot be used for fields and methods within an interface. Fields methods or constructor declared private are strictly controlled, which means they cannot be access bt anywhere outside the enclosing class. A standar design strategy is to make all fields private and provide public getter methods for them.

Back

Super()

Front

represents the current instance of a parent/base class Used to call the default constructor of the parent/base class Used to access methods of the base class Used for pointing the superclass instance Must be the first line of a block

Back

What is a package in Java?

Front

It is collection of classes with a related purpose.

Back

What are access modifiers in Java?

Front

Are special keywords which are used to restrict the access of a class, constructor, data member and method in another class

Back

This()

Front

represent the current instance of a class Used to call the default constructor of the same class Used to access methods of the current class Used for pointing thecurrent class instance Must be the first line of a block

Back

Encapsulation

Front

Keeping details (like data and procedures) together in one part of a program so that programmers working on other parts of the program don't need to know about them.

Back

Class

Front

Is a bluePrint that contains fields and methods that describe the behavior of an object

Back

Inheritance

Front

The process where one class acquires the properties of another

Back

Difference between equal() and ==

Front

One is the method and the other is operator We can use == operators for reference comparison(address comparison) and .equals() method for content comparison

Back

Overriding

Front

Declaring a method in sub class which is already present in parent class is know as method overriding. Overriding is done so that a child class can give its own implementation to a method which is already provided by the parent class.

Back

What is Collection Class in Java

Front

Is a framework that acts as an architecture for storing and manipulating a group of objects. Using Collections you can perform varius tasks like searching, sorting, insertion, manipulation, deletion

Back

What is JIT compiler in Java?

Front

Java-In-Time compiler is a program that helps in converting the java bytecode into instructions that are sent directly to the processor.

Back

ArrayList vs Vector

Front

1)ArrayList is not synchronized, Vector is synchronized 2)ArrayList increments 50% of current array size if the number of elements exceeds from its capacity and vector 100% 3)ArrayList is not a legacy class. Its introduced in JDK and vector is a legacy class 4)ArrayList is fast because it is non-synchronized and vector is opositive 5)ArrayList uses the Iterator interface to traverse the elements and Vector can use the iterator interface or Enumeration interface to traverse the elements

Back