Introduction
Java is a programming language and
environment invented by James Gosling and others in 1994. Java was originally
named Oak and was developed as a part of the Green project at the Sun Company.
About JAVA
Java is a high-level object-oriented programming
language developed by the Sun Microsystems. Though it is associated with the
World Wide Web but it is older than the origin of Web. It was only developed
keeping in mind the consumer electronics and communication equipments. It came
into existence as a part of web application, web services and a platform
independent programming language in the 1990s.
Java is influenced by C, C++ and borrowed
some advanced features from some other languages. It is platform independent,
you can “Write Once Run Anywhere” that means it can develop and run on any
device equipped with Java Virtual Machine (JVM). This language is applicable in
all kinds of operating systems including Linux, Windows, etc.
Procedure Oriented Programming
The procedure oriented programming (POP)
focuses on creating and ordering procedures of the code keeping in mind to
achieve a specific job. The key features of this kind of use procedures,
sequencing of procedures and sharing global data.
Object Oriented Programming
A type of programming in which programmers
define not only the data type of a data structure, but also the types of
operations that can be applied to the data structure. In this way, the data
structure becomes an object that includes both data and functions. In addition,
programmers can create relationships between one object and another. For
example, objects can inherit characteristics from other objects.
One of the principal advantages of
object-oriented programming techniques over procedural programming techniques
is that they enable programmers to create modules that do not need to be
changed when a new type of object is added. A programmer can simply create a
new object that inherits many of its features from existing objects. This makes
object-oriented programs easier to modify.
To perform object-oriented programming, one
needs an object-oriented programming language (OOP). Java, C++ is the
object-oriented programming language.
JVM
(Java Virtual Machine) – Program written in java are
compiled into java byte code, which is then interpreted by a special java
interpreter for any specific platform and this java interpreter is known as
Java Virtual Machine.
Byte Code – is a machine instruction for a java processor chip called
JVM. The byte code is independent of the computer system it has to run upon.
OOP’s Principle
Object Oriented programming follows the
following principle also known as OOPs Principle.
Encapsulation - Conceals the exact details of how a
particular class works from objects that use its code or send messages to
it. Encapsulation is achieved by specifying which classes may use
the members of an object. The result is that each object exposes to any class a
certain interface — those members accessible to that class.
Polymorphism - Polymorphism is an
object-oriented programming term. The ability to have methods with the same
name, but different content, for related classes. The procedure to use is
determined at run time by the class of the object. Function overloading,
constructor overload is one of the example.
Abstraction - Identifying the distinguishing
characteristics of a class or object without having to process all the
information about the class or object.. Represent essential features of a
system without getting involvement with the complexity of the entire system.
Inheritance – Inheritance is where in some
cases, a class will have "subclasses," more specialized versions of a
class. Subclasses inherit attributes and behaviors from their parent
classes, and can introduce their own. A class can inherit methods and properties
from another class. This is known as inheritance. The class that your subclass
is inheriting from is known as the superclass.
Interface : An interface is a named collection of method
definitions without implementations. An interface can also include constant
declarations. Often interfaces are touted as an alternative to multiple class
inheritance.
Binding : Associating a name with its referent.
Specifically, locating the object named by a signature, putting it into its
running state if it isn't already, and returning an interface pointer to it.
Objects can be bound at run time also called late binding or dynamic
binding or at compile time also called static binding. See also
Moniker and Running state.
Characteristic, Structures and Miscellaneous
Class - A class is a model that defines the
variables and the methods that common to all objects of a certain kind. A class
is an abstract type. A class defines the abstract characteristics of an
object, including its attributes, fields or properties and also its behaviors
or methods or features. For example, the class Dog would consist of
quality shared by all dogs, for example breed, fur colour etc. In other way, a class is a
collection of methods and properties. A class file also can contain inner private
classes. A java source file is allowed only one public class per file. A class
either can be standalone or be extended from another class (inheritance) or can
implement one or more interfaces (interfaces). A subclass can access both
protected and public members of the superclass.
Object - An object means an instance. An object
is a software bundle of variables related methods. An object is a
particular instance of a class. The set of values of the attributes of a
particular object is called its state.
Instance - It’s an object-oriented programming term. An object created
from a class definition. Unlike a class, which is just a definition, an
instance actually exists as an object that can be used to perform tasks.
Modularity - The source code for an object can be
written and maintained independently of the source code for other object and an
object can be used easily by someone else in the system.
Comment - A comment is a remark from programmer to explain some aspect
of the code to who is reading the source code. Comments can be anything
including or excluding programming syntax as compiler ignore it.
a) Single line comments -
Comments followed the // symbols
b) Multiline Comments – The are used
for comments spread over many line. They begin with /* and end with */.
Type Casting - A type cast provides a method for
explicit conversion of the type of an object in a specific situation. The
compiler treats cast-expression as type type-name after a type
cast has been made. Casts can be used to convert objects of any scalar type to
or from any other scalar type. Explicit type casts are constrained by the same
rules that determine the effects of implicit conversions.
Implicit conversion : Implicit conversions do not require any
operator. They are automatically performed when a value is copied to a
compatible type. For example:
short a=2000;
int b;
b=a;
Explicit conversion : Many conversions, specially those that
imply a different interpretation of the value, require an explicit conversion.
We have already seen two notations for explicit type conversion: functional and
c-like casting:
double a=2000.566;
int b;
b = (int) a; // c-like cast notation
statements
consist of tokens,
expressions, and other statements. A statement that forms a component of
another statement is called the “body” of the enclosing statement. Each
statement type given by the following syntax is discussed in this chapter.
Compound Statements (Blocks) - A compound statement consists of zero or
more statements enclosed in curly braces ({ }). A compound statement can be
used anywhere a statement is expected. Compound statements are commonly called
“blocks.”
Multithreading - The ability of an operating system to
execute different parts of a program, called threads, simultaneously. The
programmer must carefully design the program in such a way that all the threads
can run at the same time without interfering with each other.
Wrapper Classes - In order to convert from external numeric
format to internal format, Java uses the parseInt() method of the Integer class, Double class and Float class. The method requires a
standard Java string as parameter. The Integer class is sometimes called a wrapper
class
Array - An array is a group of same typed variables that are
referenced by a common name. Arrays can be any typed and one or more
dimensions. A particular element can be addressed by array name and index of
the array enclosed in third bracket ([]). Array can be declared with its
initial values or can be defined with the size and can input the values latter.
An array index start from 0 by default. Length of single dimension array can
get using a function – array. length
int a[]={1,2,3,4};
double a[]=new double[10];
Method
- A method is an
object's abilities. Methods or functions are the modules from which java
program is built. Method can be declared with - access-specifier,
modifier, type, method-name(parameter list), where access specifer
is optional. Methods also known as functions. access-specifier – private/
public/protected.
protected keyword is a modifier that can be used in the declaration of
methods or variables. A protected variable or method is only visible within its
class, within its subclasses, or within the class package.
private keyword is a modifier that can be used in the declaration of
methods or variables. Using the private modifier in the declaration for either
of these types hides the methods and variables so they cannot be directly
referenced outside of the class they're declared in. One exception to this rule
is that private methods or variables declared within a class can also be used
by inner classes.
public keyword is a modifier that can be used in the declaration of
classes and interfaces. The public keyword can also be used as a modifier in
the declaration of methods and variables. Classes or interfaces declared as
public are visible everywhere. Methods and variables declared as public are
visible everywhere their corresponding classes are visible.
(Note that the protected, public,
private keyword cannot be used in the declaration of local variables.)
type – Type is compulsory for a method declaration. Type
declaration indicates that what types of values going to be returned. void (no
return) or int / float / double / Boolean / char –(if a function
return a value it not compulsory to accept a parameter form caller method).
Information hiding – An object has a public interface that
other objects can communicate with it. The object can maintain private
information and methods that can changed at any time without affecting the
other objects that depend on it.
parameter list – are variables or objects that receive the
value of argument.
actual parameter—the actual value that is passed into the
method by a caller. Actual arguments (those supplied by the caller) are evaluated.
Caller – sum(a, b)
formal parameter—the identifier used in a method to stand
for the value that is passed into the method by a caller. Receiver – int
sum(int x, int y)
Message passing - "The process by which an
object sends data to another object or asks the other object to invoke a
method. Also known to some programming languages as interfacing
Function Call by value – When a simple type passed to a method, as
a copy of the argument is being made and passed to the function is known as call
by value, any changes made to the parameter inside the function do not
affect the original. A functions parameter list also known as signature.
void test()
{
int a=10,b=20;
int s=sum(a, b);
}
Function call by reference – When an object is passed as an argument
to a method it is passed by reference. A reference to an argument is
passed as parameter, the value of the argument is not passed. This method is
called call by reference.
class testing
{
int a, b;
void test()
{
a=10,b=20;
testing t=new testing();
int s=sum(t);
}
}
Pure function – Pure function or accessor methods return
information to the caller about a state of an object without changing the
state.
Impure function – Pure function or mutator methods
return information to the caller about a state of an object by changing the
state.
Function overloading - In Java its possible to define two or
more methods or functions within the same class can have same name, however
their parameter declarations have to differ form one another its known as
Functions overloading. Functions overloading is one of the ways where
polymorphism principle implemented.
signature - A signature is a list that specifies a class constructor, an
instance method, or a static method, thereby distinguishing it from other
constructors, instance methods, or static methods. Two forms of signatures are
accepted: simple and full. A simple signature is a single element list
containing the name of the method or constructor.
Constructors -
The central player in object initialization is the constructor. In Java,
constructors are similar to methods, but they are not methods. Like a method, a
constructor has a set of parameters and a body of code. Unlike methods,
however, constructors have no return type. Like methods, you can give access
specifiers to constructors, but unlike methods, constructors with public,
protected, or package access are not inherited by subclasses. If you
don't define the any constructors, Java will generate a default no-argument
constructor for you.
When a new instance (object) of a class
created using the new keyword, a constructor for that class is called.
Constructors are used to initialize the instance variables of an object.
Constructors are similar to methods, but with a few important differences.
Differences between methods and
constructors.
1. Constructor must have the same name as the
class
2. There is no return type given in a
constructor signature (header).
3. There is no return statement in the body of
the constructor.
4. The first line of a constructor must either
be a call on another constructor in the same class (using this), or a call on
the superclass constructor (using super).
5. An access specifier can be use but
Constructor can not be typed (int, float etc.).
There are three types of constructor
Default constructor - A default constructor does not have
any parameters. It is not necessary to create a default constructor, it is
automatically created by the compiler. The default constructor initializes all
instance variables to default value. If you define any constructor for
your class, no default constructor is automatically created.
Parameterize Constructor - A parameterize constructor which can take
arguments (parameter) of any types are termed as parameterized constructors.
copy constructor – A copy constructor which can have a formal
parameter that is the type of the class, which also can refer as object. It is
used to create a copy of an existing object of the same class.
Example :
class ComplexAdd
{
double re, im;
//Default
Constructor
ComplexAdd()
{
re=im=0;
}
//Parameterize
Constructor
ComplexAdd(double r, double m)
{
re = r;
im = m;
}
//Copy
Constructor
ComplexAdd(ComplexAdd CA)
{
re = CA.re;
im
= CA.im;
}
Data Types, Literals and Identifier
Data Type - A variable is a symbolic name for a computer memory location,
while declaring a variable the program must keep track of the type of data or
information to be stored in the variable. The type in java is defined by the
data type. Primitive data types are those are not composed, it also known
as fundamental data types. Following are the eight primitive data types which
are supported by Java languages:
int - It is a 32-bit signed two's complement integer data type. It
ranges from -2,147,483,648 to 2,147,483,647. This data type is used for integer
values. However for wider range of values use long.
byte - The byte data type is an 8-bit integer. It ranges from -128
to127 , byte can be used instead of int.
short -The short data type is a 16-bit signed two's complement
integer. It ranges from -32,768 to 32,767. short is used to save memory
in array declaration.
long - The long data type is a 64-bit integer. It ranges from -9,223,372,036,854,775,808
to 9,223,372,036,854,775,807. Use this data type with larger range of
values.
float - The float data type is a single-precision 32-bit floating
point. It ranges from 1.40129846432481707e-45 to 3.40282346638528860e+38. Use a
float (instead of double) to save memory in large arrays.
double - This data type is a double-precision 64-bit
floating point. It ranges from 4.94065645841246544e-324d to
1.79769313486231570e+308d . This data type is generally the default choice for
decimal values.
boolean - The boolean data type is 1-bit and has only two values: true
and false.
char - The char data type is a single 16-bit, unsigned Unicode
character. It ranges from 0 to 65,535.
Composite Data Types - In addition to the elementary data
types Java supplies, you can also assemble items of different types to create
composite data types such as arrays, and classes. You can build composite data
types from elementary types and from other composite types.
Identifiers & Literals
Constant or Literals – A data item does not change during
execution of a program is called a constant or literals. Constant or literals
can be numeric – Integer (int) type or fractional (float or double), character
or string.
e. g. 200, “hello”,
45.0F, 444.4545, TRUE, FALSE
Identifiers or variables – Symbolic names used for various data
items in programs known as identifiers. Identifiers also can be defined as user
defined name given to memory boxed to store data or information.
Rules for naming identifiers.
- Must start with an alphabet.
- A numeric digit allowed.
- No space or symbols are allowed except an underscore.
- No java keyword can be use as identifiers.
Instance variable - Instance variables are any variables that
are defined in a constructor function and that are copied into each object
instance of that constructor. All object instances have their own copies of
instance variables. The
significance of an instance variable is that every object instantiated
from that class contains its own copy of all instance variables.
global variable - A variable whose value can be accessed
and modified by any statement in an application, and not merely within a single
routine in which it is defined. Variables declared just in side the class
known as global variable.
class testing
{
int a, b; //global variable
}
Local variable - A variable that is accessible only within
a function or procedure. Other procedures or functions cannot access this
variable's data. Their lifetime is from entry to their definition to exit from
their block / function. Use global variables to share data across many
procedures and functions, or private variables to share data with the functions
you call.
Scope and Lifetime of variables : It is common to find confusion between scope
and lifetime - though they are in cases related, they are entirely
different notions: lifetime is to do with a period of time during the
execution of a program, scope is to do with which parts of a program
text. In Java, lifetime is dynamic - you must execute the program (or do
so in a thought experiment) in order to determine it. Scope is static -
determinable at compile time, or by reading the program text. The lifetime
of a variable is the interval of time for which the variable exists; i.e.
the time from when it is created to when it is destroyed; duration, span,
or extent are equivalent terms for the same thing.
Temporary variables : Used in evaluation of an
expression, e.g. for(int i=0;i<10;i++)
Operators : An operator is a
symbol or letter, which makes the computer perform specific operation in a
programming statement.
arithmetic operator - Operators that perform numeric calculations.
In Java, the arithmetic operators are: + (addition), – (subtraction), *
(multiplication), / (division) and % (modulus).
Relational operator - An operator that manipulates numeric and
other values to produce a logical result. In Java, the relational operators are
<, >,= =, <=, >=, and !=.
unary operator - The unary assignment operators, use two
operand instead of one, for the increment (++) and decrement (– –)
operators. Its also call increment/decrement operator. a++, a--, a+=10.
Ternary Operator – Can be used to replace certain of if –
else-if statement. Its require three operands to work on. It represent by the ?
and : symbols. Expression1?Expression2:Expression3
e.g. tax = salary>10000?salary*0.05 :
0; (if variable salary stored more than 10000 then tax variable will calculated
5% of salary otherwise tax will be).
logical operator - An operator that produces a logical result
(true or false); sometimes called a Boolean operator. The logical operators in
Java are used for expression grouping, NOT or ! (negation), AND (Creates
a Boolean behavior that represents the logical AND of the given behaviors. The
behavior's value is true when both b1 and b2 are true; otherwise,
it is false, OR (Creates a Boolean behavior that represents the logical OR of
the given behaviors. The behavior's value is true when either b1 or b2
are true; otherwise it is false).
Binary Operator (Bitwise Operators) – This operator
do the binary operations between two or more variables. Also known as bits
operator. The bitwise operators perform bitwise-AND (&),
bitwise-exclusive-OR (^), and bitwise-inclusive-OR (|) operations.
E.g. 101 & 100 = 100 (Multiplication). 101 ! 100 = 101 (Addition). 101
^ 100 = 001(If one bit is 0 and the other bit is 1, the corresponding
result bit is set to 1. Otherwise, the corresponding result bit is set to 0).
Right shift >> Left shift << (The value of a
right-shift expression e1 >> e2 is e1 / 2e2,
and the value of a left-shift expression e1 << e2
is e1 * 2e2).
JAVA Keywords
Keyword – Java reserved words that convey meaning to the computer. Used
to write programming syntax. A programming syntax or statement should have at
least one keyword. e. g. class, int, if, for.
The static keyword is used as a modifier for methods and variables. When
the static keyword appears in a method or variable declaration, it means that
there will be only one copy of the method or variable that each class object
may reference, regardless of the number of instances of the containing class
that are created.
A variable that is declared with the keyword
final value can not be updated. This is handy for setting up constants.
Constants are usually written in all uppercase. The final keyword can also be
used with a method to keep a extended subclass from overriding the method.
Example: private
final int counter = 5;
If – else if – else -
The if keyword is used to execute a statement or block of statements when its
associated expression evaluates to true. An if statement may also have
an alternative else if or else clause. If the expression defined by the
if statement evaluates to false, then control transfers to the statement
(or block of statements) following the else if or else keyword. If
the expression defined by the if statement evaluates to true, then
control transfers to the first statement following the if keyword. Multiple
conditional expression can be written in if or else if statement
separated by logical operator but there is no expression written in else.
if ( num < 1000 ) //when num is below 1000
t=0;
else if ( num<5000) // When num is equal or over
1000 but below 5000
t=100;
else t=200; // When
num is equal or over 5000
switch - The switch keyword is used along with the keyword case,
and sometimes the keyword default, to create a conditional statement. In a switch
statement, the switch keyword is followed by an expression within
parentheses. Once the expression has been evaluated, its value is compared
against the label following each case statement within the switch
statement body. When a label has the same value, the lines following that case
statement are executed. An optional default label is included within the body
of a switch statement when there is no guarantee that the labels provided by
each case statement are the only values the switch expression may
evaluate to.
switch ( someExpression )
{
case
1 : System.out.print(“Switch-case”); break;
default
: System.out.print(“Not a Value”);
}
The break
keyword is also, at times, used within the body of a switch statement. Once the
lines following a case statement have executed, the break statement is
included to jump over the remaining body of the switch condition.
Without a break statement, subsequent case statements would continue being
evaluated, and eventually the default statement, if one were included,
would execute.
Difference between switch-case and if-else
if-else
switch-case
|
if-else-if-else
|
for - The for keyword is used to create a
loop construct. An initialization section, an expression section, and an update
section immediately follow the keyword. A semicolon separates each section, and
all appear together within at least one set of parentheses. The initialization
section allows the programmer to declare one or more local loop variables with
initial values. The expression or final value section contains an expression
that is evaluated to determine whether the loop should continue or how long it
should continue. A true result allows the loop to continue; a false
result allows control to transfer to the statement following the loop body. The
update section allows to increment loop counters or perform other updates.
Typically, the update section is used to increment or decrement whatever loop
counters the programmer defines.
for ( int i = 0; i
< 10; i++ )
while - The while keyword is used to create a loop construct.
In a while loop, the expression in parentheses immediately following the
keyword is evaluated, and if the result is true, the statements appearing
within the loop body are executed. If multiple statements make up the body of
the loop, they must be enclosed with curly braces. Once the loop body has
executed, control transfers back to the top of the loop where the test is
performed again, and the execution of the loop body is repeated until the value
of the expression evaluates to false. While is a entry centered
loop as it check the condition and then perform the body.
while ( i < 10 )
{
System.out.println("Printing
in loop");
}
do-while - The do keyword is used as part of a do/while
loop. Unlike the other, more commonly used loop constructs, a do/while loop
expression is evaluated only after the block of code within its body has been
executed. Thus, you are ensured that the code within the loop body is executed
at least once, even if the expression tested causes the loop to end. . Do-while
is an exit centered loop as it does not check any condition but perform the
body once and then check the condition. A semicolon is required after the
condition (while) in a do/while loop.
do
{
System.out.println("Printing
at least once");
} while ( i <= 10 );
while –
do-while Difference
while
|
do-while
|
Jump
Statement – Jump statement
used to transfer control to another part of the program. break, continue worked
as jump statement in java.
break - statement used to terminate a sequence in switch statement.
Also exit a loop depend on programmer wish.
while(a<10)
{
if(a==5)
break;
}
continue – can be used only in loop to terminate
that particular process and transfer control to the loop conditional
expression.
while(a<10)
{
if(a==5)
continue;
}
break and
continue Difference
break can be used a jump statement in any type
of loops and switch-case.
break jump directly out of the body of the loop
or switch-case statement and follow the next statement onwards.
|
continue can be used in loop but not in switch-case
continue transfer control to conditional
expression not quite the loop.
|
new - The new keyword is used as an
operator for creating a new object or array. The new operator can be used to
allocate dimensional arrays for any numeric or object type. Once an array has
adequate space allocated, all the elements of the array are initialized to a
default value, and it is then up to the programmer to supply values other than
the defaults. Using the new keyword to create an array typically looks like
this:
int array[] = new int[10];
When new is used to create an object, it
first creates an instance of the specified class, then initializes all of the
instance variables to their default values, and last invokes the appropriate
constructor for the class, depending on the arguments provided in the argument
list. Using the new keyword to create a class object typically looks like this:
ClassTest ct=new ClassTest();
this - Calls another
constructor in same class. Often a constructor with few parameters will call a
constructor with more parameters, giving default values for the missing
parameters. Use this to call other constructors in the same class. The keyword this may be used
only in the body of an instance method or constructor, or in the initializes of
an instance variable of a class. If it appears anywhere else, a error will
occur. e.g.
class test
{
int a;
test(int a)
//Parameterize Constructor
{
this.a=a;
}
}
super(). Use super to call a constructor in a
parent class. Calling the constructor for the superclass must be the first
statement in the body of a constructor. If you are satisfied with the default
constructor in the superclass, there is no need to make a call to it because it
will be supplied automatically.
System class - The System
class provides access to the native operating system's environment through the
use of static methods. The System
class also provides very basic IO
streams for console read, write and error operations. System.in.read()
reads a keystroke and returns an integer value. System.out.println(string)
displays a string to the current output device.
escape sequence
• An escape sequence is a series of
characters that represents a special character
• An escape sequence begins with a backslash
character (\), which indicates that the character(s) that follow should be
treated in a special way
\n
|
newline
|
\t
|
Tab
|
\b
|
Backspace
|
\f
|
form feed
|
\r
|
Return
|
\"
|
" (double quote)
|
\'
|
' (single quote)
|
\\
|
\ (back slash)
|
The package keyword is used by Java to specify which
package the code in the file is located in. Java code that is part of a
particular package has access to all classes in the package, and all
non-private methods and variables in those classes. E. g. java.lang (is a
package name), java.lang.Math (here Math is a class and when we use a function
of these class like Math.pow(), pow() is a method of class Math from package
java.lang. We can create our own package and can import to a program in need.
IO package - The program uses various classes (such as BufferedReader and
InputStreamReader) that are defined in the java.io package. It is, thus,
necessary to import this package to use these classes.
Exceptions - One of the important characteristics of any program designed
to be used there are likely to be a mistakes while entering data into the
program. The professional must attempt to detect or catch user input errors.
The Java try/catch mechanism is a very good way of doing this. The
statement throws IOException also does the same purpose. Specific types
of errors can be handled by specific type of exception.
Java have two types of exceptions, checked
and unchecked. where Exception which requires being catches and handled during
compile time and unchecked exception catches during runtime.
Some example of
Checked and Unchecked Exception
Exception
|
Reason
|
ArrayIndexOutOfBoundsException
|
When Array index
is out of bounds
|
ArrayStoreException
|
Thrown to indicate
that an attempt has been made to store the wrong type of object into an array
of objects.
|
ArithmeticException
|
Throws an
Arithmetic error, such as divide-by-zero.
|
ClassCastException
|
attempted to cast
an object to a subclass of which it is not an instance.
|
IllegalArgumentException
|
Illegal argument
used while invoking a method.
|
IllegalThreadStateException
|
Requested
operation not compatible with current thread state.
|
IndexOutOfBoundsException
|
Some type of index
is out-of-bounds.
|
NegativeArraySizeException
|
Array created with
a negative size.
|
NullPointerException
|
Invalid use of a
null reference.
|
NumberFormatException
|
Invalid conversion
of a string to a numeric format.
|
StringIndexOutOfBounds
|
Attempt to index
outside the bounds of a string.
|
Following is
the list of Java Checked Exceptions Defined in java.lang.
Exception
|
Reason
|
ClassNotFoundException
|
Class not found.
|
CloneNotSupportedException
|
When attempted to
clone an object but the does not implement the Cloneable interface.
|
InterruptedException
|
One thread has
been interrupted by another thread.
|
NoSuchFieldException
|
A requested field
does not exist.
|
NoSuchMethodException
|
A requested method
does not exist.
|
finally() - When a value is thrown from the
try statement and the try has one or more catch that
catches it and transfer the control to the first such catch clause. However, the finally block always executes when the try block exits and even there is no exception
is thrown.
BufferedReader - Read text from a character-input stream,
buffering characters so as to provide for the efficient reading of characters,
arrays, and lines.
InputStreamReader - is a bridge from byte streams to character
streams: It reads bytes and translates them into characters according to a
specified character encoding. The encoding that it uses may be specified by
name, or the platform's default encoding may be accepted.
Each invocation of one of an
InputStreamReader's read() methods may cause one or more bytes to be read from
the underlying byte-input stream. For top efficiency, consider wrapping an
InputStreamReader within a BufferedReader; for example,
BufferedReader br = new
BufferedReader(new InputStreamReader(System.in));
readLine() method belongs to the class BufferedReader and accept a data stream from input
device as a form of String. A BufferedReader
object must be associated with an InputStreamReader
which in turn must be associated with an InputStream
object.
Example
BufferedReader br = new
BufferedReader(new InputStreamReader(System.in));
System.out.println("Enter a Name : ");
String name=br.readLine();
System.out.println("Enter a age : ");
int age =Integer.parseInt(br.readLine();
System.out.println("Enter a Salary : ");
double age =Double.parseDouble(br.readLine();
System.out.println("Enter Male or Female (M/F): ");
char mf =(char)br.readLine().charAt(0);
FILE
What are Files?
Output of the programs that we had written
are temporary so the results derived after running the programs are lost after
execution. Java allows data to be stored permanently in a data file with
the help of an extensive set of library functions for handling these data files
Opening and Closing a Data file:
To store data in a file, the data needs to
be transferred from the computer's memory to the data file in the storage media
like the hard disk. However the data that is output does not go directly
to the disk when an output command is issued. Instead it goes to a
temporary storage area in memory called a buffer. Even if the buffer is
not full, the data in the buffer can be forcibly transferred to the file, if
required.
Example
FileWriter fr=new
FileWriter("name.txt");
BufferedWriter br1=new BufferedWriter(fr);
// open a file “name.txt” for writing
FileReader fr=new
FileReader("name.txt");
BufferedReader br=new
BufferedReader(fr); // open a file “name.txt” for Reading
Byte Streams : The package java.io provides two set of
class hierarchies - one for handling reading and writing of bytes, and another
for handling reading and writing of characters. The abstract classes
InputStream and OutputStream are the root of inheritance hierarchies handling
reading and writing of bytes respectively.
Reader and Writer classes - Similar to the InputStream and
OutputStream class hierarchies for reading and writing bytes, Java technology
provides class hierarchies rooted at Reader and Writer classes for reading and
writing characters.
Scanner class
read data from standard input device - The
Scanner class is a class in java.util, which allows the user to read values of
various types. Read different type of values from either the keyboard or
file without having to convert them from strings and determine if there are more
values to be read.
separate the tokens - The
Scanner class also looks for tokens in the input. A token is a series of
characters that ends with what Java calls whitespace. To read a line that
has a series of values separated by blanks, the scanner will take each values
as a separate token.
Used for File operation – In
example below, if the file "emp.txt" is not found, a
FileNotFoundException is thrown. This checked for exception, so "throws
FileNotFoundException" can be used on the header of the method.
Scanner read = new Scanner(new
FileReader("emp.txt"));
Example :
Reading Data from Keyboard :
Scanner sc = new Scanner(System.in);
System.out.print("Enter your full name: ");
String name = sc.nextLine();
// Read a Line
System.out.print("Enter Designation: ");
String desi = sc.next();
// Read a Word
System.out.print("Age : ");
int age = sc.nextInt();
// Read a Integer Value
System.out.print("Enter Salary : ");
double sal = sc.nextDouble();
// Read a double Value
For Separating the Tokens
Scanner sc = new Scanner("1, 2, 3, 4, 5, 6, 7, 8, 9,
10").useDelimiter(", ");
while
(sc.hasNext())
{
String num = sc.next();
System.out.println(num);
}
PrintWriter -PrintWriter prints formatted
representations of objects to a text-output stream. In other words, you can say
it enables to write formatted data to a writer. It implements all of the print
methods found in PrintStream and does not contain methods for writing bytes.
For instance, writing int, long and other primitive data formatted as text.
Example
PrintWriter
PR=new PrintWriter(System.out,true);
PR.println("Hello");
double
a=4.5e-7;
int x=123;
System.out.println(a);
PR.println(a);
PR.println("%1$"+x);
String and
StringBuffer() - String is immutable that once the value assigned to
object cannot be modified. Suppose if we want to perform concatenation another
string object will be prepared and the value is going to assign for that
object. In total we are having 2 objects
StringBuffer is Mutable
we can change the value of the object even the value is assigned to the
object.
Example :
Assign the following
String st = "Hello";
StringBuffer st = new
StringBuffer("Hello");
When we use the
following statement :
st= st + "to Java
World" - It will allocate a new memory space.
st.append("to Java
World") - simply allocate a new memory space to only 2nd statement and add
to link to previous name.
StringBuffer
StringBuffer - is mainly used for the dynamic string
concatenation which enhances the performance. Some of its class members :
append() - This is the append() function used for the concatenate the
string in string buffer. str1.append(str2)..
insert() - This is the insert() function used to insert any string or
character at the specified position in the given string.
reverse() - This is the reverse() function used to
reverse the string present in string buffer.
charAt() : This is the charAt() function which is used to get the
character at the specified position of the given string.
length() - This is the length() function is used to finding the length
of the buffered string.
StringTokenizer
StringTokenizer : The string tokenizer class allows an
application to break a string into tokens. The set of delimiters (the characters
that separate tokens) may be specified either at creation time or on a
per-token basis.
Example
StringTokenizer st = new
StringTokenizer("this is a test");
while (st.hasMoreTokens())
{
System.out.println(st.nextToken());
}
prints
the following output:
this
is
a
test
String Functions – String class from package java.lang have
some methods which can manipulate string literals.
String.length() – to find the length of a string value.
String.charAt(int) – extract a character from the said string
from given position.
String1.equals(String2) – check equality between two string and
return a Boolean value as result.
String1.equalsIgnorecase(String2) - check equality between two strings while
ignoring he case difference and return a Boolean value as result.
String1.compareTo(String2) – Compare between two string( relevant to
the ASCII values of each character), if both equal it return 0, if String1 is
smaller than String2 then it will return -1 and if String1 is bigger than
String2 then it will return 1.
String.substring(int) – Extract all the string from given
position until end.
String.substring(int,int) - Extract all the string from starting
position up to left of end position.
String1.concat(String1) – Join String2 to the right of String1.
This can be done by: String1=String1+ String2.
String.indexOf(char/string) - Returns the index within this string of
the first occurrence of the specified character.
String.indexOf(char/string, int) - Returns the index within this string of
the first occurrence of the specified character, starting the search at the
specified index.
String.lastIndexof(char/String) - Returns the index within this string of
the last occurrence of the specified character.
String.firstIndexof(char/String) - Returns the index within this string of
the first occurrence of the specified character
String.startswith(String) -Tests if this string starts with the
specified prefix.
String.endsWith(String) - Tests if this string ends with the
specified suffix.
String.trim() - Removes white space from both ends of
this string.
String.replace(char, char) - Returns a new string resulting from
replacing all occurrences of oldChar in this string with newChar.
String.toLowerCase() / String.toUpperCase() -
Converts this String to lowercase / Converts this String to upper
case.
String.valueOf(String) - Returns a new Integer object initialized to the
value of the specified e.g. String.String
x="12"; int y=Integer.valueOf(x);
String.toCharArray() -Converts this string to a new character
array.
Math Functions - The class Math from package
java.lang contains methods for performing basic numeric operations such as the
elementary exponential, logarithm, square root, and trigonometric functions.
Math.abs(double) - Returns the absolute value of a double
value.
Math.sqrt(double) - Returns the square root of a double
value.
Math.pow(double, double) - Returns of value of the first argument
raised to the power of the second argument.
Math.min(double, double) – Returns the smaller of two double
values.
Math.max(double, double) – Returns the larger of two double
values.
Math.sin(double) / Math.cos(double) / Math.tan(double)
- Returns the trigonometric sine, cosine and tangent of an angle.
Math.exp(double) - Returns the exponential number e
(i.e., 2.718...) raised to the power of a double value.
Math.ceil(double) - Returns the smallest (closest to
negative infinity) double value that is not less than the argument and
is equal to a mathematical integer. Math. ceil(12.5) = 13, Math.ceil(-12.5)
= -12
Math.floor(double) - Returns the largest (closest to positive
infinity) double value that is not greater than the argument and is
equal to a mathematical integer. Math.floor(12.5) = 12, Math.floor(-12.5) =
-13.
Math.random(double) - Returns a random number between 0.0
and 1.0.
Math.round(double) - Returns the closest long to the
argument.
Math.rint(double) - Returns the closest double value
that is equal to a mathematical integer..
e.g. double d=56.678; will give 57.0 and double d=56.478 will give 56.0.
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