Java Interview Questions

Front 1

abstraction

Back 1

process of separating ideas from instances

focuses on object behavior

Front 2

What does abstraction do?

Back 2

Abstraction facilitates the development of classes in terms of their functionality instead of their implementation details.

Front 3

How does Java support abstraction?

Back 3

Java supports the creation and existence of abstract classes that expose interfaces without including the implementation of all methods.

Front 4

interface attributes

Back 4

- Members of an interface are public by default

- Variables in an interface are final by default

- A class an inherit from more than one interface, but only one class

- All interface methods are implicitly abstract

Front 5

abstract class attributes

Back 5

- A class an inherit from more than one interface, but only one class

- An abstract class can inherit from an interface without implementation

- An abstract cannot be instantiated, but can be invoked if it has a main()

Front 6

interface

Back 6

A set of methods that can be called on an object that does NOT provide concrete implementations for all methods

Front 7

polymorphism

Back 7

The provision of single interface to entities of different types

Front 8

What does polymorphism facilitate?

Back 8

Polymorphism enables one to "program in the general"

Polymorphism enables one to write programs that process objects that share the same superclass or interface as if they are all objects of the class

Front 9

Array attributes

Back 9

- Arrays can contain primitives or objects

- Arrays have a fixed size

- class Array has fewer methods than ArrayList

Front 10

ArrayList attributes

Back 10

- ArrayList can only contain objects; must use autoboxing/unboxing for primitives

- ArrayList size is dynamic

- ArrayList has more methods than Array (addAll, removeAll, iterator, etc.

Front 11

static

Back 11

keyword that allows a member variable or method to be accessed without requiring the instatiation of its class

Front 12

information hiding

Back 12

strategy to provide abstraction

Front 13

encapsulation

Back 13

mechanism that binds together code and data it manipulates and keeps both safe from outside interference and misuse.

Front 14

What does an interface facilitate?

Back 14

- useful for assigning common functionality to unrelated classes

- allows unrelated classes to be processed polymorphically

Front 15

iterator

Back 15

interface that provides methods that are able to iterate over any collection

each Java Collection contains an iterator method that returns an iterator instance

Front 16

difference between Exception and Error

Back 16

- class Exception is used for exceptional conditions that a user's program should catch

- class Error defines exceptions that are not expected to be caught by a user program

- both are subclasses of Throwable

Front 17

map

Back 17

- Collection object that maps keys to values

- cannot contain duplicate keys

Front 18

pass by value

Back 18

- a copy of the object or primitive is passed

- changes made to the data do not affect the original value

Front 19

list

Back 19

- ordered collection that can contain duplicate elements

Front 20

primitive data types

Back 20

- byte

- short

- int

- long

- float

- double

- char

- boolean

Front 21

set

Back 21

Collection that cannot contain duplicate elements

Front 22

basic interfaces of Java Collections Framework

Back 22

- Collection

- Set

- List

- Map

Front 23

collection

Back 23

- represents a group of objects known as elements

Front 24

Comparable

Back 24

interface with one method: compareTo(T o)

Front 25

throw vs. throws

Back 25

- throw is used to explicity raise an exception

- throws is used to indicate exceptions not handled by a method

Front 26

pass by reference

Back 26

- reference (memory location or hashcode) is passed

- changes made by the method are reflected everywhere

Front 27

ArrayList

Back 27

- index-based structure, backed by an Array

- provides random access to elements; O(1) search

- consumes less memory than LinkedList

Front 28

LinkedList

Back 28

- stores data as list of elements with links to .next() and .previous()

- O(n) search

- insertion is faster with LinkedList than ArrayList; no resizing or index update

- LinkedList consumes more memory than ArrayList due to next and previous references

Front 29

access modifiers

Back 29

- public

- private

- protected

- default (package)

Front 30

public modifier scope

Back 30

world

Front 31

private modifier scope

Back 31

class

Front 32

protected modifier scope

Back 32

package and subclasses

Front 33

default modifier scope

Back 33

package

Front 34

software development life cycle

Back 34

- analysis

- design

- implementation

- mirror

- planning

Front 35

finalize()

Back 35

called by garbage before releasing memory

Front 36

inheritance

Back 36

- process by which one object acquires the properties of another object.

- creation of new class by absorbing an existing class's members and embellishing them with new or modified capabilities

- facilitates code reuse

Front 37

superclass

Back 37

original class from which a new class inherits

Front 38

subclass

Back 38

new class that inherits from an older class

Front 39

direct superclass

Back 39

subclass is closest descendant

Front 40

indirect superclass

Back 40

subclass is above direct superclass

Front 41

types of polymorphism

Back 41

- ad-hoc

- parametric: generic programming

- subtyping: name may denote instances of different classes related by a superclass or interface

Front 42

ad-hoc polymorphism

Back 42

function overloading

Front 43

parametric polymorphism

Back 43

generic programming

Front 44

subtype polymorphism

Back 44

name may denote instances of different classes related by a superclass or interface

Front 45

JVM

Back 45

Java Virtual Machine

Front 46

purpose of JVM

Back 46

- execute Java bytecode

- allow Java to run on any platform

Front 47

encapsulation

Back 47

packing of data and methods into a single software component

Front 48

purpose of encapsulation

Back 48

- used to control access to data members and functions

- access to private data is restricted to object members and methods

Front 49

autoboxing/unboxing

Back 49

automatic conversion made by the Java compiler between primitive types and their corresponding wrapper classes

- autobox: primitive -> wrapper

- unbox: wrapper -> primitive

Front 50

garbage collection

Back 50

- automatic algorithm that reclaims space that is occupied by dereferenced objects

- can be manually triggered by Object.finalize(), though not advised

Front 51

purpose of garbage collection

Back 51

- identify and discard objects that are no longer needed by the application

- reclaim system resources for new use

Front 52

immutable object

Back 52

object cannot be modified after it is created

Front 53

benefits of immutable objects

Back 53

- inherently thread safe

- simpler

- offers higher security

Front 54

method overloading

Back 54

methods of the same name can be declared in the same class as long as they have different sets of parameters

Front 55

purpose of method overloading

Back 55

commonly used to create several methods with the same name that perform a similar task with different data types or a different number of arguments

Front 56

abstract class

Back 56

- incomplete class for which one never intends to create objects

- used only as superclass in inheritance hierarchies

- abstract methods do not provide implementation

Front 57

ACN stock price

Back 57

- 5 year growth from 37 to 90

- 1 year: traded between 75 and 90 from

- currently about 85

Front 58

core value: stewardship

Back 58

build a stronger company for future generations

Front 59

Comparator

Back 59

interface with two methods:

- compare(T o1, T o2)

- equals(T o)

Front 60

JRE

Back 60

- Java Runtime Environment

- basically the JVM (where programs execute)

Front 61

JDK

Back 61

- Java Development Kit

- includes JRE, compilers and development tools

Front 62

core value: best people

Back 62

attract, develop and retain the best talent

Front 63

core value: stewardship

Back 63

build a stronger company for future generations

Front 64

core value: client value creation

Back 64

- help clients perform at a high-level

- create long-term relationships by being responsive, relevant and consistently delivering value

Front 65

core value: one global network

Back 65

leverage institutional knowledge to deliver value to the client

Front 66

core value: respect for the individual

Back 66

- value diversity

- foster a trusting and inclusive environment

Front 67

core value: integrity

Back 67

- say what you mean

- match words to action

Front 68

method overriding

Back 68

instance method in a subclass with same signature and return type as an instance method in the superclass replaces functionality of the superclass's method

Front 69

@Override

Back 69

annotation helps assure method is overriding instead of overloading

Front 70

checked exception

Back 70

must be declared in a method or constructor's throws clause

Front 71

unchecked exception

Back 71

doesn't need to be declared in a method or constructor's throws clause if the exception can propagate beyond the scope of the original call

Front 72

priority queue

Back 72

- unbounded queue, based on priority heap

- developer can provide Comparator upon creation

- does not allow null values, object without natural ordering or objects without a Comparator associated

- not thread safe

- requires O(n log n) for enqueing and dequeing operations

Front 73

Unicode

Back 73

internal representation of characters and strings

uses 16 bits to represent each other

Front 74

System.gc()

Back 74

explicit call for garbage collection

Front 75

transient

Back 75

modifiier that applies to variables only and it is not stored as part of its object’s Persistent state. Transient variables are not serialized.

Front 76

volatile

Back 76

modifier that applies to variables only and it tells the compiler that the variable modified by volatile can be changed unexpectedly by other parts of the program.

Front 77

inner class

Back 77

classes defined in other classes, including those defined in methods are called inner classes. An inner class can have any accessibility including private

nested classes can lead to more readable and maintainable code; increases encapsulation

Front 78

anonymous class

Back 78

class defined inside a method without a name and is instantiated and declared in the same place and cannot have explicit constructors.

Front 79

reflection

Back 79

java.lang.reflect package has the ability to analyze itself in runtime.

Front 80

String vs StringBuilder

Back 80

- String is immutable

- StringBuilder is mutable

Front 81

StringBuilder vs StringBuffer

Back 81

- StringBuilder is single-threaded

- StringBuffer is multithreaded