What is Java?
Java is:
Object Oriented, Platform independent: Simple ,Secure ,Architectural-
neutral ,Portable ,Robust ,Multi-threaded Interpreted ,High Performance ,Distributed ,Dynamic
Difference between C, C++ and Java?
C++ is the advanced version of 'C" language. So, the basic difference between C++ and JAVA are as given below - Java is a true object oriented language while c++ is a object oriented language.
In "C" we use the concept of pointers whereas there are no pointers used in JAVA.
Java does not support operator overloading but "C" is support.Java provides the multi-threading capability while in "C" is not possible.
C++ SUPPORTS THE CONCEPT OF
1.POINTERS
2.TEMPLATES AND
3.VIRTUAL FUNCTIONS
C vs C++:
*C does not have classes and objects (C does not support OOP)
*Structures in C cannot have functions.
*C does not have namespaces (namespaces are used to avoid name collisions).
*The I/O functions are entirely different in C and C++ (ex: printf( ), scanf( ) etc. are part of the C language).
*You cannot overload a function in C (i.e. you cannot have 2 functions with the same name in C).
*Better dynamic memory management operators are available in C++.
*C does not have reference variables (in C++ reference variables are used in functions).
*In C constants are defined as macros (in C++ we can make use of ‘const’ to declare a constant).
*Inline functions are not available in C.
c is a topdown approach while c++ is bottom up approach
1.What are the principle concepts of OOPS?
There are four principle concepts upon
which object oriented design and programming rest. They are:
ñ
Abstraction
ñ
Polymorphism
ñ
Inheritance
ñ Encapsulation
(i.e. easily remembered as A-PIE).
2.What is Abstraction?
Abstraction refers to the act of
representing essential features without including the background details or
explanations.
3.What is Encapsulation?
Encapsulation is a technique used for
hiding the properties and behaviors of an object and allowing outside access
only as appropriate. It prevents other objects from directly altering or
accessing the properties or methods of the encapsulated object.
4.What is the difference between abstraction and encapsulation?
ñ
Abstraction focuses on the
outside view of an object (i.e. the interface) Encapsulation (information hiding) prevents clients from seeing
it’s inside view, where the behavior of the abstraction is implemented.
ñ
Abstraction solves the
problem in the design side while Encapsulation
is the Implementation.
ñ Encapsulation is the deliverables of Abstraction.
Encapsulation barely talks about grouping up your abstraction to suit the
developer needs.
5.What is Inheritance?
ñ
Inheritance
is the process by which objects of one class acquire the properties of objects
of another class.
ñ
A
class that is inherited is called a superclass.
ñ
The
class that does the inheriting is called a subclass.
ñ
Inheritance
is done by using the keyword extends.
ñ
The
two most common reasons to use inheritance are:
ñ
To
promote code reuse
ñ To use polymorphism
6.What is Polymorphism?
Polymorphism is briefly described as
"one interface, many implementations." Polymorphism is a
characteristic of being able to assign a different meaning or usage to
something in different contexts - specifically, to allow an entity such as a
variable, a function, or an object to have more than one form.
7.How does Java implement polymorphism?
(Inheritance, Overloading and Overriding
are used to achieve Polymorphism in java).
Polymorphism manifests itself in Java in the form of multiple methods having the same name.
Polymorphism manifests itself in Java in the form of multiple methods having the same name.
ñ
In
some cases, multiple methods have the same name, but different formal argument
lists (overloaded methods).
ñ In other cases,
multiple methods have the same name, same return type, and same formal argument
list (overridden methods).
8.Explain the different forms of Polymorphism.
There are two types of polymorphism one
is Compile time polymorphism and the
other is run time polymorphism. Compile time polymorphism is method
overloading. Runtime time polymorphism
is done using inheritance and interface.
Note: From a practical programming viewpoint, polymorphism manifests itself in three distinct forms in Java:
Note: From a practical programming viewpoint, polymorphism manifests itself in three distinct forms in Java:
ñ
Method
overloading
ñ
Method
overriding through inheritance
ñ Method overriding through the Java interface
9.What is runtime polymorphism or dynamic method dispatch?
In Java, runtime polymorphism or dynamic
method dispatch is a process in which a call to an overridden method is
resolved at runtime rather than at compile-time. In this process, an overridden
method is called through the reference variable of a superclass. The
determination of the method to be called is based on the object being referred
to by the reference variable.
10.What is Dynamic Binding?
Binding refers to the linking of a procedure
call to the code to be executed in response to the call. Dynamic binding (also
known as late binding) means that the code associated with a given procedure
call is not known until the time of the call at run-time. It is associated with
polymorphism and inheritance.
11.What is method overloading?
Method Overloading means to have two or
more methods with same name in the same class with different arguments. The
benefit of method overloading is that it allows you to implement methods that
support the same semantic operation but differ by argument number or type.
Note:
Note:
ñ
Overloaded
methods MUST change the argument list
ñ
Overloaded
methods CAN change the return type
ñ
Overloaded
methods CAN change the access modifier
ñ
Overloaded
methods CAN declare new or broader checked exceptions
ñ A method can be overloaded in the same class or in a
subclass
12.What is method overriding?
Method overriding occurs when sub class
declares a method that has the same type arguments as a method declared by one
of its superclass. The key benefit of overriding is the ability to define
behavior that’s specific to a particular subclass type.
Note:
Note:
ñ
The overriding
method cannot have a more restrictive access modifier than the method being
overridden (Ex: You can’t override a method marked public and make it
protected).
ñ
You cannot
override a method marked final
ñ You cannot override a method marked static
13.What are the differences between method overloading and method overriding?
|
Overloaded
Method
|
Overridden
Method
|
Arguments
|
Must change
|
Must not change
|
Return type
|
Can change
|
Can’t change except for
covariant returns
|
Exceptions
|
Can change
|
Can reduce or eliminate. Must
not throw new or broader checked exceptions
|
Access
|
Can change
|
Must not make more restrictive
(can be less restrictive)
|
Invocation
|
Reference type determines which
overloaded version is selected. Happens at compile time.
|
Object type determines which
method is selected. Happens at runtime.
|
14.Can overloaded methods be override too?
Yes, derived classes still can override
the overloaded methods. Polymorphism can still happen. Compiler will not
binding the method calls since it is overloaded, because it might be overridden
now or in the future.
15.Is it possible to override the main method?
NO, because main is a static method. A
static method can't be overridden in Java.
16.How to invoke a superclass version of an Overridden method?
To invoke a superclass method that has
been overridden in a subclass, you must either call the method directly through
a superclass instance, or use the super prefix in the subclass itself. From the
point of the view of the subclass, the super prefix provides an explicit
reference to the superclass' implementation of the method.
// From subclass
super.overriddenMethod();
17.What is super?
super is a keyword
which is used to access the method or member variables from the superclass. If
a method hides one of the member variables in its superclass, the method can
refer to the hidden variable through the use of the super keyword. In the same
way, if a method overrides one of the methods in its superclass, the method can
invoke the overridden method through the use of the super keyword.
Note:
Note:
ñ
You can only go
back one level.
ñ In the constructor, if you use super(), it must be
the very first code, and you cannot access any this.xxx variables
or methods to compute its parameters.
18.How do you prevent a method from being overridden?
To prevent a specific method from being
overridden in a subclass, use the final modifier on the method declaration,
which means "this is the final implementation of this method", the
end of its inheritance hierarchy.
public final void exampleMethod() {
// Method statements
}
19.What
is an Interface?
An interface is a description of a set
of methods that conforming implementing classes must have.
Note:
Note:
ñ
You can’t mark
an interface as final.
ñ
Interface
variables must be static.
ñ An Interface cannot extend anything but another
interfaces.
20.Can
we instantiate an interface?
You can’t instantiate an interface
directly, but you can instantiate a class that implements an interface.
21.Can
we create an object for an interface?
Yes, it is always necessary to create an
object implementation for an interface. Interfaces cannot be instantiated in
their own right, so you must write a class that implements the interface and
fulfill all the methods defined in it.
22.Do
interfaces have member variables?
Interfaces may have member variables,
but these are implicitly public,
static, and final-
in other words, interfaces can declare only constants, not instance variables
that are available to all implementations and may be used as key references for
method arguments for example.
23.What modifiers are allowed for methods in an Interface?
Only public and abstract
modifiers are allowed for methods in interfaces.
24.What is a marker interface?
Marker interfaces are those which do not
declare any required methods, but signify their compatibility with certain
operations. The java.io.Serializable
interface and Cloneable
are typical marker interfaces. These do not contain any methods, but classes
must implement this interface in order to be serialized and de-serialized.
25.What is an abstract class?
Abstract classes are classes that
contain one or more abstract methods. An abstract method is a method that is
declared, but contains no implementation.
Note:
Note:
ñ
If even a single
method is abstract, the whole class must be declared abstract.
ñ
Abstract classes
may not be instantiated, and require subclasses to provide implementations for
the abstract methods.
ñ You can’t mark a class as both abstract and final.
26.Can we instantiate an abstract class?
An abstract class can never be
instantiated. Its sole purpose is to be extended (subclassed).
27.What are the differences between Interface and Abstract class?
Abstract Class
|
Interfaces
|
An
abstract class can provide complete, default code and/or just the details
that have to be overridden.
|
An
interface cannot provide any code at all,just the signature.
|
In
case of abstract class, a class may extend only one abstract class.
|
A
Class may implement several interfaces.
|
An
abstract class can have non-abstract methods.
|
All
methods of an Interface are abstract.
|
An
abstract class can have instance variables.
|
An
Interface cannot have instance variables.
|
An
abstract class can have any visibility: public, private, protected.
|
An
Interface visibility must be public (or) none.
|
If
we add a new method to an abstract class then we have the option of providing
default implementation and therefore all the existing code might work
properly.
|
If
we add a new method to an Interface then we have to track down all the
implementations of the interface and define implementation for the new
method.
|
An
abstract class can contain constructors .
|
An
Interface cannot contain constructors .
|
Abstract
classes are fast.
|
Interfaces
are slow as it requires extra indirection to find corresponding method in the
actual class.
|
28.When should I use abstract classes and when should I use interfaces?
Use Interfaces when…
ñ
You
see that something in your design will change frequently.
ñ
If
various implementations only share method signatures then it is better to use
Interfaces.
ñ you need some
classes to use some methods which you don't want to be included in the class,
then you go for the interface, which makes it easy to just implement and make
use of the methods defined in the interface.
Use Abstract Class when…
ñ
If
various implementations are of the same kind and use common behavior or status
then abstract class is better to use.
ñ
When
you want to provide a generalized form of abstraction and leave the
implementation task with the inheriting subclass.
ñ Abstract classes
are an excellent way to create planned inheritance hierarchies. They're also a
good choice for nonleaf classes in class hierarchies.
29.When you declare a method as abstract, can other nonabstract methods access it?
Yes, other nonabstract methods can
access a method that you declare as abstract.
30.Can there be an abstract class with no abstract methods in it?
Yes, there can be an abstract class
without abstract methods.
31.What is Constructor?
ñ
A
constructor is a special method whose task is to initialize the object of its
class.
ñ
It
is special because its name is the same as the class name.
ñ
They
do not have return types, not even void and therefore they
cannot return values.
ñ
They
cannot be inherited, though a derived class can call the base
class constructor.
ñ Constructor is
invoked whenever an object of its associated class is created.
32.How does the Java default constructor be provided?
If a class defined by the code does not
have any constructor, compiler will automatically provide one no-parameter-constructor
(default-constructor) for the class in the byte code. The access modifier
(public/private/etc.) of the default constructor is the same as the class
itself.
33.Can constructor be inherited?
No, constructor cannot be inherited,
though a derived class can call the base class constructor.
34.What are the differences between Contructors and Methods?
|
Constructors
|
Methods
|
Purpose
|
Create an instance of a class
|
Group Java statements
|
Modifiers
|
Cannot be abstract, final,
native, static, or synchronized
|
Can be abstract, final,
native, static, or synchronized
|
Return Type
|
No return type, not even void
|
void or a valid return type
|
Name
|
Same name as the class (first
letter is capitalized by convention) -- usually a noun
|
Any name except the class.
Method names begin with a lowercase letter by convention -- usually the name
of an action
|
this
|
Refers to another constructor
in the same class. If used, it must be the first line of the constructor
|
Refers to an instance of the
owning class. Cannot be used by static methods.
|
super
|
Calls
the constructor of the parent class. If used, must be the first line of the
constructor
|
Calls
an overridden method in the parent class
|
Inheritance
|
Constructors
are not inherited
|
Methods
are inherited
|
35.How are this() and super() used with constructors?
ñ
Constructors
use this to refer to another constructor in the same class with a
different parameter list.
ñ Constructors use
super to invoke the superclass's constructor. If a constructor uses super,
it must use it in the first line; otherwise, the compiler will complain.
36.What are the differences between Class Methods and Instance Methods?
Class Methods
|
Instance Methods
|
Class
methods are methods which are declared as static. The method can be called
without creating an instance of the class
|
Instance
methods on the other hand require an instance of the class to exist before
they can be called, so an instance of a class needs to be created by using
the new keyword.
Instance methods operate on specific instances of classes. |
Class
methods can only operate on class members and not on instance members as
class methods are unaware of instance members.
|
Instance
methods of the class can also not be called from within a class method unless
they are being called on an instance of that class.
|
Class
methods are methods which are declared as static. The method can be called
without creating an instance of the class.
|
Instance
methods are not declared as static.
|
37.How are this() and super() used with constructors?
ñ
Constructors
use this to refer to another constructor in the same class with a
different parameter list.
ñ Constructors use
super to invoke the superclass's constructor. If a constructor uses
super, it must use it in the first line; otherwise, the compiler will complain.
38.What are Access Specifiers?
One of the techniques in object-oriented
programming is encapsulation. It concerns the hiding of data in a
class and making this class available only through methods. Java allows you to
control access to classes, methods, and fields via so-called access
specifiers..
39.What are Access Specifiers available in Java?
Java offers four access specifiers,
listed below in decreasing accessibility:
ñ
Public- public
classes, methods, and fields can be accessed from everywhere.
ñ
Protected- protected
methods and fields can only be accessed within the same class to which the
methods and fields belong, within its subclasses, and within classes of the
same package.
ñ
Default(no
specifier)- If
you do not set access to specific level, then such a class, method, or field
will be accessible from inside the same package to which the class, method, or
field belongs, but not from outside this package.
ñ Private- private methods and fields
can only be accessed within the same class to which the methods and fields
belong. private methods and fields are not visible within subclasses
and are not inherited by subclasses.
Situation
|
public
|
protected
|
default
|
private
|
Accessible
to class
from same package? |
yes
|
yes
|
yes
|
no
|
Accessible
to class
from different package? |
yes
|
no, unless
it is a subclass
|
no
|
no
|
40.What is final modifier?
The final modifier keyword
makes that the programmer cannot change the value anymore. The actual meaning
depends on whether it is applied to a class, a variable, or a method.
ñ
final Classes- A final class cannot have subclasses.
ñ
final Variables- A final variable cannot be changed
once it is initialized.
ñ final
Methods-
A final method cannot be overridden by subclasses.
41.What
are the uses of final method?
There are two reasons for marking a
method as final:
ñ
Disallowing
subclasses to change the meaning of the method.
ñ Increasing
efficiency by allowing the compiler to turn calls to the method into inline
Java code.
42.What is static block?
Static block which exactly executed
exactly once when the class is first loaded into JVM. Before going to the main
method the static block will execute.
43.What are static variables?
Variables that have only one copy per
class are known as static variables. They are not attached to a particular
instance of a class but rather belong to a class as a whole. They are declared
by using the static keyword as a modifier.
static type varIdentifier;
where, the name of the variable is
varIdentifier and its data type is specified by type.
Note: Static variables that are not explicitly initialized in the code are automatically initialized with a default value. The default value depends on the data type of the variables.
Note: Static variables that are not explicitly initialized in the code are automatically initialized with a default value. The default value depends on the data type of the variables.
44.What is the difference between static and non-static variables?
A static variable is associated with the
class as a whole rather than with specific instances of a class. Non-static
variables take on unique values with each object instance.
45.What
are static methods?
Methods declared with the keyword static
as modifier are called static methods or class methods. They are so called
because they affect a class as a whole, not a particular instance of the class.
Static methods are always invoked without reference to a particular instance of
a class.
Note:The use of a static method suffers from the following restrictions:
Note:The use of a static method suffers from the following restrictions:
ñ
A static method
can only call other static methods.
ñ
A static method
must only access static data.
ñ A static method cannot reference to
the current object using keywords super or this.
46.What
is an Iterator ?
ñ
The
Iterator interface is used to step through the elements of a Collection.
ñ
Iterators
let you process each element of a Collection.
ñ
Iterators
are a generic way to go through all the elements of a Collection no
matter how it is organized.
ñ Iterator is
an Interface implemented a different way for every Collection.
47.How do you traverse through a collection using its Iterator?
To use an iterator to traverse through
the contents of a collection, follow these steps:
ñ
Obtain
an iterator to the start of the collection by calling the collection’s iterator()
method.
ñ
Set
up a loop that makes a call to hasNext(). Have the loop iterate as
long as hasNext() returns true.
ñ Within the loop,
obtain each element by calling next().
48.How do you remove elements during Iteration?
Iterator also has a method remove()
when remove is called, the current element in the iteration is deleted.
49.What is the difference between Enumeration and Iterator?
Enumeration
|
Iterator
|
Enumeration doesn't have a
remove() method
|
Iterator has a remove() method
|
Enumeration acts as Read-only
interface, because it has the methods only to traverse and fetch the objects
|
Can be abstract, final,
native, static, or synchronized
|
Note: So Enumeration
is used whenever we want to make Collection objects as Read-only.
50.How is ListIterator?
ListIterator is just like Iterator, except it allows us to
access the collection in either the forward or backward direction and lets us
modify an element
51.What is the List interface?
ñ
The
List interface provides support for ordered collections of objects.
ñ Lists may
contain duplicate elements.
52.What are the main
implementations of the List interface ?
The main implementations of the List
interface are as follows :
ñ
ArrayList :
Resizable-array implementation of the List interface. The best all-around
implementation of the List interface.
ñ
Vector : Synchronized
resizable-array implementation of the List interface with additional
"legacy methods."
ñ LinkedList : Doubly-linked list implementation of
the List interface. May provide better performance than the ArrayList
implementation if elements are frequently inserted or deleted within the list.
Useful for queues and double-ended queues (deques).
53.What are the advantages of ArrayList over arrays ?
Some of the advantages ArrayList has
over arrays are:
ñ
It
can grow dynamically
ñ It provides more
powerful insertion and search mechanisms than arrays.
54.Difference between ArrayList and Vector ?
ArrayList
|
Vector
|
ArrayList
is NOT synchronized by default.
|
Vector
List is synchronized by default.
|
ArrayList
can use only Iterator to access the elements.
|
Vector
list can use Iterator and Enumeration Interface to access the elements.
|
The
ArrayList increases its array size by 50 percent if it runs out of room.
|
A
Vector defaults to doubling the size of its array if it runs out of room
|
ArrayList
has no default size.
|
While
vector has a default size of 10.
|
55.How
to obtain Array from an ArrayList ?
Array can be obtained from an ArrayList
using toArray() method on ArrayList.
List arrayList = new ArrayList();
arrayList.add(…
Object a[] = arrayList.toArray();
56.Why
insertion and deletion in ArrayList is slow compared to LinkedList ?
ñ
ArrayList
internally
uses and array to store the elements, when that array gets filled by inserting
elements a new array of roughly 1.5 times the size of the original array is
created and all the data of old array is copied to new array.
ñ During deletion,
all elements present in the array after the deleted elements have to be moved
one step back to fill the space created by deletion. In linked list data is
stored in nodes that have reference to the previous node and the next node so
adding element is simple as creating the node an updating the next pointer on
the last node and the previous pointer on the new node. Deletion in linked
list is fast because it involves only updating the next pointer in the
node before the deleted node and updating the previous pointer in the node
after the deleted node.
57.Why are Iterators
returned by ArrayList called Fail Fast ?
Because, if list is structurally
modified at any time after the iterator is created, in any way except through
the iterator's own remove or add methods, the iterator will throw a
ConcurrentModificationException. Thus, in the face of concurrent modification,
the iterator fails quickly and cleanly, rather than risking arbitrary,
non-deterministic behavior at an undetermined time in the future.
58.How do you decide
when to use ArrayList and When to use LinkedList?
If you need to support random access,
without inserting or removing elements from any place other than the end, then
ArrayList offers the optimal collection. If, however, you need to frequently
add and remove elements from the middle of the list and only access the list
elements sequentially, then LinkedList offers the better implementation.
59.What is the Set interface ?
ñ
The
Set interface provides methods for accessing the elements of a finite
mathematical set
ñ
Sets
do not allow duplicate elements
ñ
Contains
no methods other than those inherited from Collection
ñ
It
adds the restriction that duplicate elements are prohibited
ñ Two Set objects
are equal if they contain the same elements
60.What
are the main Implementations of the Set interface ?
The main implementations of the List
interface are as follows:
ñ
HashSet
ñ
TreeSet
ñ
LinkedHashSet
ñ EnumSet
61.What
is a HashSet ?
ñ
A
HashSet is an unsorted, unordered Set.
ñ
It
uses the hashcode of the object being inserted (so the more efficient your
hashcode() implementation the better access performance you’ll get).
ñ Use this class
when you want a collection with no duplicates and you don’t care about order
when you iterate through it.
62.What
is a TreeSet ?
TreeSet is a Set implementation that
keeps the elements in sorted order. The elements are sorted according to the
natural order of elements or by the comparator provided at creation time.
63.What is an EnumSet ?
An EnumSet is a specialized set for use
with enum types, all of the elements in the EnumSet type that is specified,
explicitly or implicitly, when the set is created.
64.Difference between HashSet and TreeSet ?
HashSet
|
TreeSet
|
HashSet
is under set interface i.e. it does not guarantee for either sorted
order or sequence order.
|
TreeSet
is under set i.e. it provides elements in a sorted order (acceding
order).
|
We
can add any type of elements to hash set.
|
We
can add only similar types
of elements to tree set. |
65.What is a Map ?
ñ
A
map is an object that stores associations between keys and values (key/value
pairs).
ñ
Given
a key, you can find its value. Both keys and values are objects.
ñ
The
keys must be unique, but the values may be duplicated.
ñ Some maps can
accept a null key and null values, others cannot.
66.What are the main Implementations of the Map interface ?
The main implementations of the List
interface are as follows:
ñ
HashMap
ñ
HashTable
ñ
TreeMap
ñ EnumMap
67.What is a TreeMap ?
TreeMap actually implements the
SortedMap interface which extends the Map interface. In a TreeMap the data will
be sorted in ascending order of keys according to the natural order for the
key's class, or by the comparator provided at creation time. TreeMap is based
on the Red-Black tree data structure.
68.How do you decide when to use HashMap and when to use TreeMap ?
For inserting, deleting, and locating elements
in a Map, the HashMap offers the best alternative. If, however, you need to
traverse the keys in a sorted order, then TreeMap is your better alternative.
Depending upon the size of your collection, it may be faster to add elements to
a HashMap, then convert the map to a TreeMap for sorted key traversal.
69.Difference between HashMap and Hashtable ?
HashMap
|
Hashtable
|
HashMap
lets you have null values as well as one null key.
|
HashTable
does not allows null values as key and value.
|
The
iterator in the HashMap is fail-safe (If you change the map while iterating,
you’ll know).
|
The
enumerator for the Hashtable is not fail-safe.
|
HashMap
is unsynchronized.
|
Hashtable
is synchronized.
|
Note: Only one NULL
is allowed as a key in HashMap. HashMap does not allow multiple keys to be
NULL. Nevertheless, it can have multiple NULL values.
70.How does a Hashtable
internally maintain the key-value pairs?
TreeMap actually implements the
SortedMap interface which extends the Map interface. In a TreeMap the data will
be sorted in ascending order of keys according to the natural order for the
key's class, or by the comparator provided at creation time. TreeMap is based
on the Red-Black tree data structure.
71.What Are the different
Collection Views That Maps Provide?
Maps Provide Three Collection Views.
ñ
Key Set - allow a map's
contents to be viewed as a set of keys.
ñ
Values
Collection
- allow a map's contents to be viewed as a set of values.
ñ Entry Set - allow a map's contents to be viewed
as a set of key-value mappings.
72.What is a KeySet View ?
KeySet is a set returned by the keySet()
method of the Map Interface, It is a set that contains all the keys present in
the Map.
73.What is a Values Collection View ?
Values Collection View is a collection
returned by the values() method of the Map Interface, It
contains all the objects present as values in the map.
74.What is an EntrySet View ?
Entry Set view is a set that is returned
by the entrySet() method in the map and contains Objects of type Map.
Entry each of which has both Key and Value.
75.How do you sort an ArrayList (or any list) of user-defined objects ?
Create an implementation of the java.lang.Comparable
interface that knows how to order your objects and pass it to java.util.Collections.sort(List,
Comparator).
76.What is the Comparable interface ?
The Comparable interface is used to sort
collections and arrays of objects using the Collections.sort()
and java.utils.Arrays.sort()
methods respectively. The objects of the class implementing the Comparable
interface can be ordered.
The Comparable interface in the generic
form is written as follows:
interface Comparable<T>
where T is the name of the type parameter.
All classes implementing the Comparable interface must implement the compareTo() method that has the return type as an integer. The signature of the compareTo() method is as follows:
All classes implementing the Comparable interface must implement the compareTo() method that has the return type as an integer. The signature of the compareTo() method is as follows:
int i = object1.compareTo(object2)
ñ
If
object1 < object2: The value of i returned will be negative.
ñ
If
object1 > object2: The value of i returned will be positive.
ñ If object1 =
object2: The value of i returned will be zero.
77.What are the differences between the Comparable and Comparator interfaces ?
Comparable
|
Comparato
|
It uses the compareTo()
method.
int objectOne.compareTo(objectTwo).
|
t
uses the compare() method.
int compare(ObjOne, ObjTwo) |
It
is necessary to modify the class whose instance is going to be sorted.
|
A
separate class can be created in order to sort the instances.
|
Only
one sort sequence can be created.
|
Many
sort sequences can be created.
|
It
is frequently used by the API classes.
|
It
used by third-party classes to sort instances.
|
EmoticonEmoticon