Java concepts Theory
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Theory Type 1: Definition of OOPS Concepts
1.What is Object Oriented Programming (OOP)?
Object Oriented Programming is a programming approach based on the concept of “Objects” which can contain data in terms of fields and procedure.
2.What is JVM?
JVM is an acronym for Java Virtual Machine; it is an abstract machine which provides the runtime environment in which Java bytecode can be executed.
3.What is Class & Object?
Class:
A
class is a blueprint representing a set of objects that share common characteristics
and behavior.
Object:
Object
is an entity with a specific identity and having specific characteristics and
specific behavior.
4.What id Data abstraction, Encapsulation, Modularity , Inheritance, polymorphism?
Data Abstraction:
Data
abstraction or abstraction refers to the act of representing essential features
without using the background details.
Practical tips: (no need to write this in the answer sheet)**
As an example, we do not know the code behind
Scanner class and its methods like nextInt() , nextDouble() etc. But we know
how to use them. That is being called as Abstraction. If you move the
steering of a car right , the car will move to the right. So we all know this
method. But by which technique it happens, we do not know. This concept of
hiding background details is being called as method abstraction.
|
Encapsulation:
The
wrapping of data and functions (that operate on data) into single unit (called
class) is known as encapsulation.
Practical tips: (no need to write this in the
answer sheet)**
As an example, We know the method names of Scanner
class. Methods like nextInt(), nextDouble. But we do not know the variable
names used inside. Because those variables are hidden inside the class. This
concept is being called as Encapsulation.
|
Modularity:
The
act of partitioning a program into individual components is called modularity.
Practical tips: (no need to write this in the
answer sheet)**
Modularity is mainly maintained by
functions/methods. Rather doing all the calculation together, in math class ,
xy can be done by pow function, sine value can be determined by a
separate function named “sin”. So in short, one function for one type of
work.
|
Inheritance:
Inheritence
is the capability of one class of things to inherit or derive the capabilities
or properties from another class.
Practical
tips: (no need to write this in the answer sheet)**
class a
{
int
x=10;
}
class b extends a
{
}
class c
{
public
static void main(String args[])
{
b obj = new b ();
System.out.println(“the value is “ + obj.x)
}
}
In the above program, class b does not contain
anything. But as it is extending the class a, so class b is able to get the
variable x inside it.
|
Polymorphism:
Polymorphism
is a property by which the same message can be sent to objects of several different
classes and each object can respond in a different way depending on its class.
Practical tips: (no need to write this in the
answer sheet)**
class Math { public void add(int a, int b) //add method adding two integers { System.out.println(a+b); } public void add(float a, float b) //add method adding two floats { System.out.println(a+b); } } class Overload { public static void main(String args[]) { Math ob = new Math(); ob.add(1,2); ob.add(2.5f,4.5f); }
}
|
5.What is Byte Code?
Bytecode is program code that has been compiled from source code into low-level code , designed for a software interpreter.
6.What is token, literal , Identifier, variable , constant, Keywords?
Token:
Smallest
individual unit in a program is called a token.
Literal:
Literals
are data items that are fixed data values. There are several kinds of literals
available in java. Like Integer literals, Floating point literals, Boolean
literals, character literals etc.
Identifier:
Identifiers
are the names given by the programmer to various program units of java.
Identifiers are the names of variables, methods, classes etc.
Variable:
Variable
is a named memory location which holds a data value of a particular datatype.
Constant:
Constant
value represents a named value that remains fixed throughout an entire program
. We can declare a constant using “Final” keyword.
Keyword:
a
keyword is a word with a predefined meaning in Java programming language
syntax. Reserved for Java, keywords may not be used as identifiers for naming
variables, classes, methods or other entities.
Practical tips: (no need to
write this in the answer sheet)**
void meth ()
{
int x = a + 5 ;
}
Token à “void” ,
“meth” , “int” , “x” , “=” , “a” , “+” , “5” , “;”
Literal à “5”
Identifier à “x” , “a”
, “meth”
Variable à “x” , “a”
Keywords à “void” ,
“int”
Operator à “=”
(assignment operator) , “+” (binary
mathematical operator)
Punctuator à “;”
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7.What is datatype? What are the different types of datatypes?
Datatype is used to
identify the type of data and associated operations of handling it.
There are 2 types of datatypes as below:
i.
Primitive Datatype / Fundamental
Datatype
ii.
Reference Datatype / Derived Datatype
8.What are primitive datatype and reference data type?
Primitive Datatype:
Primitive
datatype or fundamental datatypes are provided by language and are not based on
any other datatypes. It is used to define and hold a value of basic type in
named variable.
Reference Datatype:
Reference
datatype are created using the primitive datatypes. A reference datatype is
used to store memory address of an object.
Practical tips: (no need to write this in the
answer sheet)**
{ int x=10; } class datatype_demo { public static void main(String args[]) { a ob1=new a(); // reference datatype int ob2; // primitive datatype }
}
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9.What is operator? What are the different types of operator? Give examples for each type.
Operator:
An operator is a symbol that tells the compiler or interpreter to perform specific mathematical, relational, logical operations and produce final results.
Types of operator:
i.
Mathematical operator (example: + , - , * , / , % )
ii.
Increment/Decrement operator ( example: ++ , -- )
iii.
Relational operator (example:
> , < , >= , <= , == , != )
iv.
Logical operator (example:
&&, || , !)
v.
Assignment operator ( example:= )
10.What is fall through?
Fall of control to the following cases of matching case is called fall through.
Practical tips: (no need to write this in the answer sheet)**
{ public static void main(String args[]) { int a=2; switch (a) { case 1: System.out.println("one"); case 2: System.out.println("two"); case 3: System.out.println("three"); case 4: System.out.println("four"); break; case 5: System.out.println("five"); } }
}
Here, output will be “ two three four” , because
if we do not put “break” statement, it will keep falling and keep executing
the statements.
|
11.What is jump statement? What is the use of break and continue statement?
The statements that cause unconditional control-transfer in program are called jump statements. Two most common jump statements are break and continue.
Break statement:
When
Break statement is used inside switch , it ends the case. When break statement
is executed inside a loop, the loop terminated and program control resumes at
the next statement following the loop.
Continue statement:
When
Continue statement is executed from inside a loop, from that point all
remaining statements in the body of the loop are skipped and loop proceeds with
the next iteration.
12.How is the if…else if combination more general than a switch statement?
Switch statement must be controlled by a single integer control variable and each case section corresponds to a single constant value for the variable. The if .. else if combination allows any kind of condition supporting all types of comparisons after each if.
13.What is type conversion? What is explicit and implicit type conversion?
Type conversion means converting a variable of one data type to another.
There are 2 categories of Type Conversion as follows:
Explicit type conversion:
When we are assigning a larger type value to a variable of smaller type, then we need to perform explicit type casting.
Implicit type conversion:
When we are assigning a smaller type value to a variable of larger type, then this type of conversion happens automatically. This type of conversion is called as implicit type casting.
Practical tips: (no need to write this in the
answer sheet)**
{ public static void main(String args[]) { int a=5; double b=9.5; b=a; // implicit type conversion a=(int) b; // explicit type conversion }
}
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14.What is access specifier? What are the access levels or specifiers supported by java?
Access specifiers control access to members of a class from within a java program.
Access levels available in java:
i.
Public
ii.
Privateiii. Protected
iv. Default
15.What is wrapper class?
Wrapper classes are
specially designed classes that act as wrappers to primitive data types so that
primitive values can be accessed as objects.
16.What are the advantages of Encapsulation?
Advantages of encapsulation are as follows:
i.
Data hiding
ii.
Implementation logics are hiddeniii. Flexibility
iv. More control in programmer’s hand
17.What is Data hiding?
Data hiding is a software development technique specifically used in object-oriented programming (OOP) to hide internal object details (data members). Data hiding ensures exclusive data access to class members and protects object integrity by preventing unintended or intended changes.
18.What is the use of Final Keyword?
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 the 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 value of a variable can not be changed if we put a final in front of that.
Practical tips: (no need to write this in the
answer sheet)**
Example
1: Use of “Final” keyword in front of a class
{ } class b extends a //will throw an error, because you can not extend a final class {
}
Example
2: Use of “Final” keyword in front of a method
{ final void meth1() { System.out.println("hi"); } void meth2() { System.out.println("hello"); } } class b extends a { void meth1() // will throw an error, because you can not override meth1() { System.out.println("hi again"); } void meth2() // you can override meth2() { System.out.println("hello again"); }
}
Example
3: Use of “Final” keyword in front of a variable
{ public static void main(String... ar) { final int a=5; a++ // this line will throw an error, as you can not change the value of a final variable }
}
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19.What is the use of Static Keyword?
static keyword is mainly
used for memory management. It can be used with variables, methods, blocks and
nested classes. It is a keyword which is used to share the same variable or
method of a given class. Basically, static is used for a constant variable or a
method that is same for every instance of a class.
Practical tips: (no need to write this in the answer sheet)**
{ static int x; int y; } class b { public static void main(String... ar) { a ob1=new a(); a ob2=new a(); a ob3=new a(); ob1.x=10; ob1.y=100; ob2.x=20; ob2.y=200; ob3.x=30; ob3.y=300;
System.out.println("
x--> "+ob1.x +" & y--> "+ob1.y); //prints “x--> 30 & y --> 100”
System.out.println("
x--> "+ob2.x +" & y--> "+ob2.y); //prints “x--> 30 & y --> 200”System.out.println(" x--> "+ob3.x +" & y--> "+ob3.y); //prints “x--> 30 & y --> 300” System.out.println(" one version of x--> "+a.x); // as there is one version of x, we can call it by its class name }
}
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20.What is ternary operator in java??
Java ternary
operator is the only conditional operator that takes three operands. It’s a one
liner replacement for if-then-else statement and used a lot in java
programming. We can use ternary operator if-else conditions or even switch
conditions using nested ternary operators.
Practical tips: (no need to write this in the answer sheet)**
if(a>10) { b=1; } else { b=0; } it can be written as the following way
b=(a>10)?1:0;
if(a>10) { System.out.println(“hi”); } else { System.out.println(“hello”); } it can be written as the following way System.out.println( (a>10)? ”hi” ; ”hello” ) ; if(a > b) { if ( a > c) { max=a; } else { max=c; } } else { if ( b > c) { max=b; } else { max=c; } } it can be written as the following way max = ( a>b ) ? ( (a>c)?a:c ) : ( (b>c)?b:c ) ; |
21.What is overriding?
In any
object-oriented programming language, Overriding is a feature that allows a
subclass or child class to provide a specific implementation of a method that
is already provided by one of its super-classes or parent classes.
Practical
tips: (no need to write this in the answer sheet)**
{ int x=10; void meth() { System.out.println("hi"); } } class b extends a { int x=20; // overrides the previous x void meth() // overrides the previous meth() { System.out.println( “ hello” ) ; }
}
class c { public static void main ( String args[] ) { b ob = new b (); System.out.println ( ob.x ) ; // prints 20 ob.meth(); // prints “hello” }
}
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22.What does super keyword do?
super keyword can
be used to access super class method or variable when you have overridden the
method or variable in the child class.
We can use super
keyword to invoke superclass constructor in child class constructor.
Practical
tips: (no need to write this
in the answer sheet)**
{ int x=10; void meth() { System.out.println("hello"); } } class b extends a { int x=20; void meth() { super.meth(); // it will print "hello" System.out.println(super.x) // it will print 10 }
}
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23.What is Constructor? When is it invoked?
A constructor is a special type of member-method having the same name as that of the class.
A constructor of a class is invoked automatically at the time of object creation.
24.What is Default constructor?
A constructor that accepts no parameters is called non-parameterized constructors and are also considered as default constructor.
25.Write 2 features of constructor.
i.
Constructor has the same name as that
of a classs
ii.
Constructor has no return type, not
even void.
26.What is constructor overloading?
Constructor overloading is a technique in Java in which a class can have any number of constructors that differ in parameter list. The compiler differentiates these constructors by taking into account the number of parameters in the list and their type.
27.What are the different types of constructors? Define each of them.
Default Constructor or non-parameterized constructor:
A constructor that accepts no parameters is called non-parameterized constructor and are also considered as default constructor.
Parameterized constructor:
A constructor is a member method having the same name as that of its class and no return type. It receives parameters and initialize the objects with the received values.
Practical
tips: (no need to write this in the answer sheet)**
{ int x; a() { x=1; } a( int param) { x=param; } } class b { public static void main ( String args[] ) { a ob1 = new a (); //calling default constructor a ob2 = new a ( 50 ); //calling parameterized constructor System.out.println ( ob1.x ) ; // prints 1 System.out.println ( ob2.x ) ; // prints 50 }
}
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28.What is “This” keyword? What is its significance?
Member functions of
every object have access to a magic keyword named “this”, which points to the
object itself. Thus any member function can find out the address of the object
of which it is a member.
The this keyword
represents an object that invokes a member function
Practical tips:
(no need to write this in the answer sheet)**
class
a{ int x; void meth ( int x) { this.x=x; // “this.x” denotes the class variable x, whereas “x” denotes the local variable to the function meth() } } |
29.Write the advantages of functions / methods?
i.
Functions divide complex task into
smaller , easily understandable tasks.
ii.
Functions are useful in hiding the
implementation details.
iii.
Function enhance reusability of code.
30.What are the different parts available in Method definition?
i.
Access Specifier (Example : Public,
Private, Protected, Default)
ii.
Modifier (Example: Final,
Volatile, Native etc.)
iii.
Return type (Example: void, int, float
etc.)
iv.
Method name
Practical tips: (no need to write this in the
answer sheet)**
public final void meth ( int x) { System.out.println(“hi”); }
In the above function,
Access Specifier
Ã
“public”
Modifier Ã
“Modifier”
Return type
à “Void”
Method
name à “meth”
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31.What is method/Function prototype?
Method prototype is the 1st line of the function definition that tells the program about the type of the value returned by the method and the number and type of arguments.
32.What is method signature?
Method signature refers to the number and types of arguments.
Practical tips:
(no need to write this in the answer sheet)**
void meth ( int x) { System.out.println(“hi”); }
In the above function, function prototype is :
“void meth (int x)
function signature is : “int x”
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33.What are pure and impure methods?
Pure method:
A pure method is the one that takes objects and/or primitives as arguments but does not modify the objects.
Impure method:
An impure method is the one that takes objects and changes or modifies the state of received object.
34.What is function overloading?
A function name having several definitions in the same scope that are differentiable by the number or types of their argument is said to be an overloaded function. Process of creating overload function is called function overloading.
Practical tips:
(no need to write this in the answer sheet)**
You
can use the example used in polymorphism at the first of this note.
|
35.What is package?
A package is a group or a collection that consist of related classes and interfaces. There are two types of packages in a programming language. They are the built-in packages and user-defined packages. The programming language Java consist of built-in packages such as lang, awt, javax, swing, net, io, util, sql, etc.
36.What is interface?
Interface is a mechanism of achieving abstraction and multiple inheritance. The methods in an interface are abstract methods. These methods do not have any implementation. It can also have variables or fields.
37.What are the advantages and disadvantages of Array?
Advantages:
1. It is used to represent multiple data items of same type by using only single name.
2. It can be used to implement other data structures like linked lists, stacks, queues, trees, graphs etc.
3. 2D arrays are used to represent matrices.
Disadvantages:
1. We must know in advance that how many elements are to be stored in array.
2. Array is static structure. It means that array is of fixed size. The memory which is allocated to array can not be increased or reduced.
3. Since array is of fixed size, if we allocate more memory than requirement then the memory space will be wasted. And if we allocate less memory than requirement, then it will create problem.
4. The elements of array are stored in consecutive memory locations. So insertions and deletions are very difficult and time consuming.
Theory type 2: Differences
1.Differentiate between actual and formal parameters.
Actual parameters are the parameters appearing in function call statement, that is these represent the values passed to the called function.
Formal parameters are the ones that appear in function definition , that is these represent the values received by the called function.
Practical tips: (no need to write this in the
answer sheet)**
class a { void meth( int param) // here "param" is formal parameter { System.out.println (param); } } class b { public static void main ( String args[] ) { a ob = new a (); x=5; ob.meth ( x ); // Here x is actual parameter, because we know the exact/actual value at the time of calling }
}
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2Difference between 2 ways of invoking functions?
There are following 2 ways of invoking functions:
Call by value:
By this way, the called function creates its own workcopy for passed parameters and copies the passed values in it. Any changes that take place remains intact.
Call by reference:
By this way, the called function receives the reference to the passed parameters and through this reference , it accesses the original data. Any changes that take place are reflected in the original data.
Practical tips:
(no need to write this in the answer sheet)**
class a { int x=10; void meth1(int y) { y=y+1; } void meth2(a ob) { ob.x = ob.x+1; } } class b { public static void main(String args[]) { a obj=new a(); System.out.println("value is "+ obj.x); // it will print the initial value of x as 10; obj.meth1(obj.x); System.out.println("value is "+ obj.x); // call by value can not change the original value obj.meth2(obj); System.out.println("value is "+ obj.x); // if you make any change during "call by reference" in an object, there would be permanient changes inside }
}
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3.What is the difference between class variable (static variable) and instance variable?
Static/class variable:
A data member that is declared once
for a class. All of the objects of that class type share these data members, as
there is single copy of them is available in memory.
Instance variable:
A
data member that is created for every object of the class. For n number of
object of a class, there would be n copies of instance variables, one each for
object.
Practical tips:
(no need to write this in the answer sheet)**
You can use the example used in “static
keyword” at the first of this note
(Question #19).
In that case, x will be “Class variable “
y will be “instance
variable “
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4.What is the difference between autoboxing and unboxing?
When java automatically converts a primitive type into corresponding wrapper class object (as an example from int to integer), then it is called boxing, because primitive is boxed into wrapper class while opposite case is called unboxing (When an integer object is converted into primitive int).
Since the whole
process happens automatically without writing any code for conversion it is
Practical tips:
(no need to write this in the answer sheet)**
class demo { public static void main(String args[]) { int i1=5; Integer i2= new Integer(10); i1=i2; // unboxing i2=i1; // boxing }
}
|
A class represents a set of objects that share common characteristics and behavior.
Objects are the instances of a class. Objects represents the abstraction represented by the class in the real sense.
6.What is the difference between while and do-while loop?
i.
Both types of loops repeat a block of
statements until some condition becomes false. The main difference is that in a
while loop , the test condition is tested at the beginning of the loop and in a
do-while loop , the test-condition is tested at the end of the loop.
ii.
Also it is possible that body of while
loop might not be executed at all . However the body of a do-while loop is
executed at least once since the test condition for ending the loop is not
tested until the body of the loop has been executed.
7.What is the difference between methods and constructor?
| Parameter | Constructors | Methods |
| Purpose | Creates an instance of class | Groups Java statements |
| Return type | Has no return type | Void or a valid return type |
| Name | Same name as the class | Any name except the class name |
| Execution | Called at the time of Object Creation | Called when a function call for the specific method is encountered. |
8.What is the difference between throw and throws?
| Throw | Throws |
| throw keyword is used to throw an exception explicitly. | throws keyword is used to declare one or more exceptions |
| Only single exception is thrown by using throw. | Multiple exceptions can be thrown by using throws. |
| throw keyword is used within the method. | throws keyword is used with the method signature.. |
9.What is the difference between Break and Continue?
| Break | Continue |
| A break causes the switch or loop statements to terminate the moment it is executed. Loop or switch ends abruptly when break is encountered | A continue doesn't terminate the loop, it causes the loop to go to the next iteration. |
| The break statement can be used in both switch and loop statements. | The continue statement can appear only in loops. |
| When a break statement is encountered, it terminates the block and gets the control out of the switch or loop. | When a continue statement is encountered, it gets the control to the next iteration of the loop. |
10.What is the difference between Linear and Binary search?
| Linear Search | Binary Search |
| Linear search is an algorithm to find an element in a list by sequentially checking the elements | binary search is an algorithm to find the position of a target value within a sorted array. |
| Also called sequential search. | Also called half-interval search and logarithmic search |
| It is not required to sort the array before searching | It is required to sort the array before searching. |
| Less efficient | More efficient |
11.What is the difference between Bubble and Selection sort?
| Bubble sort | Selection sort |
| A simple sorting algorithm that continuously steps through the list and compares the adjacent pairs to sort the elements. | A sorting algorithm that takes the smallest value (considering ascending order) in the list and moves it to the proper position in the array. |
| Uses item exchanging | Uses item selection |
| Takes only 1 full iteration in case of array is already arranged in sorted order. | It completes all the iterations even if the array is sorted |
12.What is the difference between Error and Exception ?
| Error | Exception |
| Recovering from Error is not possible. | We can recover from exceptions by either using try-catch block or throwing exceptions back to caller. |
| All errors in java are unchecked type. | Exceptions include both checked as well as unchecked type. |
| Errors are mostly caused by the environment in which program is running. | Program itself is responsible for causing exceptions. |
| Errors occur at runtime and not known to the compiler. | All exceptions occurs at runtime but checked exceptions are known to compiler while unchecked are not. |
| They are defined in java.lang.Error package. | They are defined in java.lang.Exception package |
13.What is the difference between If-Else block and Switch ?
- expression inside if statement decide whether to execute the statements inside if block or under else block. On the other hand, expression inside switch statement decide which case to execute.
- You can have multiple if statement for multiple choice of statements. In switch you only have one expression for the multiple choices.
- If-esle statement checks for equality as well as for logical expression . On the other hand, switch checks only for equality.
- The if statement evaluates integer, character, pointer or floating-point type or boolean type. On the other hand, switch statement evaluates only character or a integer datatype.
- Sequence of execution is like either statement under if block will execute or statements under else block statement will execute. On the other hand the expression in switch statement decide which case to execute and if you do not apply a break statement after each case it will execute till the end of switch statement.
- If expression inside if turn outs to be false, statement inside else block will be executed. If expression inside switch statement turn out to be false then default statements is executed.
- It is difficult to edit if-else statements as it is tedious to trace where the correction is required. On the other hand it is easy to edit switch statements as they are easy to trace.
| Single dimension array | Double dimension array |
| A simple data structure that stores a collection of similar type data in a contiguous block of memory. | A type of array that stores multiple data elements of the same type in matrix or table like format with a number of rows and columns. |
| Stores data as list. | Stores data in a row-column format. |
| Syntax: data_type name[]=new datatype[] | Syntax: data_type name[][]=new datatype[][] |
| Errors occur at runtime and not known to the compiler. | All exceptions occurs at runtime but checked exceptions are known to compiler while unchecked are not. |
| They are defined in java.lang.Error package. | They are defined in java.lang.Exception package |
Or,
Difference between type casting and type conversion
| Implicit type casting or type conversion | Explicit type casting or type casting |
| Implicit typecasting or type conversion is that which automatically converts one datatype into another. | When an user can convert the one datatype into other, then it is called type conversion or implicit type casting |
| Implemented only when two datatypes are compatible | Implemented on two incompatible datatypes |
| Widening conversion | Narrowing conversion |
| Casting operator is not required. | Casting operator “()” is required. |
16.Write the difference between searching and sorting
a.
In searching, a
certain array is to be searched for whereas in sorting the members of the array
are to be sorted in a particular order, i.e. descending or ascending order.
b.
Searching returns
the position of the searched array while sorting returns an array with the
elements arranged in ascending or descending order.
17.Write the difference between “.equals()” and “==”
a.
type: “==” is a
binary operator , whereas “.equals() “ is a function
b.
primitive or
objects: “==” is used to compare primitives while “.equals()” is used to check
equality of objects.
c.
Comparision: “==”
compares two objects based on memory reference. Equals method compares based on
the values
i.
Unary operators are
those that work on single operand e.g. increment operator( ++) or the decrement
operator( - - ). int a =b++; or something like int C =d- -;
ii.
Binary operators
are the one that operate on two operands e.g. ‘+’, ‘ -’, ‘ *’, ‘/’. Syntax can
be like int C=a+b;
iii.
Ternary operators
are the one that operates on three operands. It takes three argumets . 1st
argument is checked for its validity . If it is true 2nd argument is returned
else third argument is returned. For example if we write int C= a>b ? e:f;
now if a is greater than b 'e' is returned otherwise 'f' is returned.
i.
Rint() returns long
value, whereas round returns double value.
ii.
For the value like
1.5 or 9.5, rint() returns nearest lower rounded value as 1 and 9 respectively.
Whereas for round(), it returns nearest upper rounded value as 2 and 10
respectively.
A public member is
accessible from anywhere outside the class but within a program. You can set
and get the value of public variables without any member.
A private member variable
or function cannot be accessed, or even viewed from outside the class. Only the
class and friend functions can access private members.
A protected member variable
or function is very similar to a private member but it provided one additional
benefit that they can be accessed in child classes which are called derived classes.
next() method can take input till space and ends input of
getting space.
nextLine()
method can take input till the line change or new line and ends input of
getting '\n' or press enter.
22.Write the difference between package and interface
| Package | Interface |
| An organized set of related classes and interfaces | A set of fields and abstract methods that mainly allows implementing abstraction |
| Import keyword helps to access a package | Implement keyword helps to access an interface |
| Final | Finally | Finalize |
| Final is used to apply restrictions on class, method and variable. Final class can't be inherited, final method can't be overridden and final variable value can't be changed. | Finally is used to place important code, it will be executed whether exception is handled or not. | Finalize is used to perform clean up processing just before object is garbage collected. |
| It is a keyword | It is a block | It is a method |
24.Write the difference between catch() and finally()
catch
− A program catches an exception with an exception handler at the place in a
program where you want to handle the problem. The catch keyword indicates the
catching of an exception.
Finally
− The finally block is used to execute a given set of statements, whether an
exception is thrown or not thrown. For example, if you open a file, it must be
closed whether an exception is raised or not.
25.What is the difference between overloading and overriding?
| Overloading | Overriding |
| In method overloading, more than one method shares the same method name with different signature in the class. | In method overriding, derived class provides the specific implementation of the method that is already provided by the base class or parent class. |
| Method overloading may or may not require inheritance. | While method overriding always needs inheritance. |
| In this, methods must have same name and different signature. | While in this, methods must have same name and same signature. |
| It is Compile time polymorphism | It is Run time polymorphism |
| return type can or can not be be same | return type must be same |
Theory type 3: charts
1.Please specify the size of different datatypes.
Datatypes
|
Size
(in Byte)
|
Byte
|
1
|
Short
|
2
|
Int
|
4
|
Long
|
8
|
Float
|
4
|
Double
|
8
|
Char
|
2
|
2.Please specify different type of exceptions , Errors and their functionality.
Exception
|
Meaning
|
ArithmeticException
|
Arithmetic
error, such as divide-by-zero
|
ArrayIndexOutOfBoundsException
|
Array
index is out of the limit
|
NullPointerException
|
Invalid
use of NULL reference
|
NumberFormatException
|
Invalid
conversion of a string to a numeric
|
InputMismatchException
|
Wrong
type of data inserted
|
3.Please specify the string functions.
Functions
|
Functionality
|
Syntax
|
substring
|
Extract a string from a string
|
String s="SachinTendulkar"; System.out.println(s.substring(6));//Tendulkar System.out.println(s.substring(0,6));//Sachin |
compareTo
|
Compares two strings
lexicographically
|
String s1="hello"; String s2="hello"; String s3="meklo"; String s4="hemlo"; String s5="flag"; System.out.println(s1.compareTo(s2));//0 because both are equal System.out.println(s1.compareTo(s3));//-5 because "h" is 5 times lower than "m" System.out.println(s1.compareTo(s4));//-1 because "l" is 1 times lower than "m" System.out.println(s1.compareTo(s5));//2 because "h" is 2 times greater than "f" |
indexOf
|
Returns the position of the first
found occurrence of specified characters in a string
|
String s1="this is index of example"; //passing substring int index1=s1.indexOf("is");//returns the index of is substring int index2=s1.indexOf("index");//returns the index of index substring System.out.println(index1+" "+index2);//2 8 //passing substring with from index int index3=s1.indexOf("is",4);//returns the index of is substring after 4th index System.out.println(index3);//5 i.e. the index of another is //passing char value int index4=s1.indexOf('s');//returns the index of s char value System.out.println(index4);//3 |
lastIndexOf()
|
Returns the position of the last
found occurrence of specified characters in a string
|
String s1="this is index of example";//there are 2 's' characters in this sentence int index1=s1.lastIndexOf('s');//returns last index of 's' char value System.out.println(index1);//6 |
toLowerCase()
|
Converts a string to lower case
letters
|
String s=”Hello Hi”;
System.out.println(s.toLowerCase());
// “hello hi” |
To
UpperCase()
|
Converts a string to upper case
letters
|
String s=”Hello Hi”;
System.out.println(s.toUpperCase());
// “HELLO HI”
|
trim()
|
Removes whitespace from both ends of
a string
|
String s=” Hello Hi
”;
System.out.println(s.trim());
// “hello
hi”
|
startsWith()
|
Checks whether a string starts with
specified characters
|
String s=”Hello Hi”;
System.out.println(s.startsWith(“he”));
//
true
|
endsWith()
|
Checks whether a string ends with
specified characters
|
String s=”Hello Hi”;
System.out.println(s.endsWith(“hi”));
//
true
|
replace()
|
Searches a string for a specified
value, and returns a new string where the specified values are replaced
|
String s=”Hello Hi”;
System.out.println(s.replace(“e”,”aa”));
// Haallo Hi
System.out.println(s.replace(‘H’,’X’));
// Xello
Xi
|
equals()
|
Compares two strings. Returns true
if the strings are equal, and false if not
|
String s1=”Hello”;
String s2=”hello”;
String s3=”Hi”;
System.out.println(s1.equals(s2));
// False
System.out.println(s1.equals(s3));
// False
|
equalsIgnoreCase()
|
Compares two strings, ignoring case
considerations
|
String s1=”Hello”;
String s2=”hello”;
String s3=”Hi”;
System.out.println(s1.equalsIgnoreCase(s2));
// true
System.out.println(s1.equalsIgnoreCase(s3));
// False
|
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