· Java was started as a project called "Oak" by James Gosling at Sun Microsystems in June 1991, It made the promise of "Write Once, Run Anywhere", on popular platforms.

· The First publication of Java 1.0 was released by Sun Microsystems in 1995.

· In 2006-2007 Sun released java as open source and platforms independent software.

· Over time new enhanced versions of Java have been released. Like Java 1.7, 1.8, 10, 11 etc.

· Currently, Java is used in internet programming, mobile devices, games, e-business solutions, etc.

2. Explain Java Buzzwords:

· Java is an object-oriented and platform-independent programming language.

· Java has many advanced features, a list of key features is known as Java Buzz Words.

· Following are java Buzzwords that represents the Features of Java:

Simple

· Java programming language is very simple and easy to learn, understand, and code.

· Most of the syntaxes in java follow basic programming language C and object-oriented programming concepts are similar to C++.

· In a java programming language, many complicated features like pointers, operator overloading, structures, unions, etc. have been removed.

· One of the most useful features is the garbage collector it makes java more simple.

Object-oriented:

· Java is a purely object-oriented programming language (OOP). This means that Java program is developed by using classes and objects.

· In other words, to write a program in java, we need at least a class or an object.

· Object-oriented programming (OOPs) is a methodology that simplifies software development and maintenance by providing some rules.

· Basic concepts of OOPs are Object, Class, Inheritance, Polymorphism, Abstraction and Encapsulation.

· Java’s platform independence means that Java programs compiled on one machine or operating system and can be executed on any other machine or operating system without modifications. It is also called an Architecture Neutral Language.

· Java program is compiled into bytecode. This bytecode is platform independent and can be run on any machine and this bytecode format also provide security.

Secure:

· When it comes to security, Java is always the first choice.

· Java enable us to develop virus free, temper free system.

· Java program always runs in Java runtime environment (JRE) with so it is more secure.

Robust:

· Java is a robust language that can handle run-time errors.

· It checks the code during the compilation and runtime. If any runtime error is identified by the JVM, it will not be passed directly to the particular system.

· It will immediately terminate the program and stop it from causing any harm to the system.

High Performance:

· Java is an interpreted language, so it will never be as fast as a compiled language like C language.

· But, Java enables high performance with the use of (JIT) just-in-time compiler.

· The Just-In-Time (JIT) compiler is a component of the runtime environment that improves the performance of Java programs by compiling bytecodes to machine-readable code at run time.

· JIT compiler only compiles that method which is being called.

Multi-Threading:

· In simple words, when multiple tasks are running simultaneously, then it is called multi-threading.

· Java multithreading feature makes it possible to write program that can do many tasks simultaneously.

· For example, In Google Docs where we typing text, the spellings and grammatical errors are checked and autocorrect task are running.

Portable

· The WORA (Write Once Run Anywhere) concept and platform independent feature make Java portable.

· Developers can get the same result on any machine, by writing code only once.

Dynamic flexibility:

· Java provide the feature of Dynamic flexibility.

· Java is completely object-oriented programing language that provides flexibility to add classes, new methods to existing classes and even create new classes through sub-classes.

Compilation and interpretation:

· Most languages are designed as either they are compiled language or they are interpreted language.

· But java provides both functionality:

i. Java compiler for compiles the source code to bytecode and

ii. JVM for executes this bytecode to machine readable code.

3. Explain Java Editions:

· Java is a platform independent language it support multi-threaded and Secure programming.

· Java programming language is high level object oriented programming language.

· Java is distributed in three different types of editions:

1. Java Platform standard edition(SE)

2. Java Platform Enterprise edition(EE)

3. Java Platform micro edition(ME)

Java Platform Standard Edition:

· Java standard Edition is also known as Java J2SE in short term.

· Java SE provide basic functionalities such as defining types and objects, SE is a standard Java specification.

· Java SE provides high-level classes used for networking, security, database access, GUI (Graphical User Interface) development, and XML parsing.

· It is mostly used to develop APIs for Desktop Applications like antivirus software, game, etc.

· It is suitable for beginning Java developers.

Java Platform Enterprise Edition:

· Java Enterprise Edition is also known as Java J2EE in short term.

· Java Enterprise edition platform provide an API and Runtime environment for developing and running a large scale and secure network application.

· Java EE is mainly used for developing web applications.

Java Platform Micro Edition:

· Java Micro Edition is also known as Java J2ME in short term.

· Java ME facilitates the development of applications for small computing devices such as embedded systems, sensors, etc.

· It has features which make applications portable and which can run on various devices. It deals with many constraints, such as a small battery, small display, etc.

· It is mostly used to develop mobile applications.

4. Java’s Magic: The Bytecode

· Java is high-level Object-Oriented Programming language.

· Bytecode is a low-level code that is the result of the compilation of a source code, which is written, in a high-level language.

· Java bytecode is the instruction set for the (JVM) Java Virtual Machine.

· Bytecode is also one of the java's magic because this along with java virtual machine (JVM), which makes java platform independent and a secure language.

· Bytecode also makes java secure because it can be run by java virtual machine only.

· In java program (.java file) is compiled first using java compiler (javac). After successful compilation, the bytecode (.class file) of that program is generated.

· Bytecode is the code, which is generated after compiling the java program. In java (.class files) are known as byte codes.

· Following Diagram shows how the byte code is used :

· It makes java portable which helps to achieve "Write once, run anywhere" feature. It simply means you need to write the program once, and execute it at any OS.

· Generally, the size of bytecode is less than the source code, therefore it is easy and fast to transport them over the network/internet.

5. Explain JDK:

· JDK in Java is stands for Java Development Kit.

· JDK provide the collection of tools and different components that are used to develop and run java programs.

· It is a bundle of software development tools and supporting libraries combined with the Java Runtime Environment (JRE) and Java Virtual Machine (JVM).

6. Explain JVM:

· In Java JVM stands for Java Virtual Machine.

· JVM is the one that actually calls the main method present in a java code.

· JVM is the main component of Java architecture, and it is the part of the JRE (Java Runtime Environment).

· JVM is Operating System dependent, So it is responsible for allocating the necessary memory needed by the Java program and also responsible for deallocating memory space.

· following is a diagram that represent the process of JVM

· According to above diagram .java source file convert to .class file using javac compiler.

· Java compiler is based on operating system, once it converts .class file then it can be run anywhere any time in any operating system.

· And last class file run with java command to get its output using JVM means Java Virtual Machine.

7. Explain JRE:

· JRE stands for Java Run-time Environment.

· Java Run-time Environment (JRE) is the part of the Java Development Kit (JDK).

· Basically The Java source code gets compiled and converted to Java bytecode. If you wish to run this bytecode on any platform, you require JRE.

· Java Runtime Environment contains core classes, supporting files, and Java Virtual Machine (JVM).

· It provides the runtime environment.

8. Explain JDK Tools:

In Java language JDK tools can be categorized under the different category like:

· Basic tools

In basic tool contain tool used to create build application like Java, Javajdb, appletviewer, JAR etc.

Following are some basic JDK tools:

· Java:

It acts as the deployment launcher in the older SUN java. It loads the class files and interprets the source code compiled by the javac compiler.

· Javac

The javac specifies the java compiler to convert the source code into bytecode.

· Javadoc

· The Javadoc generates documentation for the comments added in the source code.

· Jar

· The jar helps the archives to manage the jar files in the package library.

· Appletviewer

· The applet viewer is designed to run and debug Java applets without the help of an internet browser.

Ø RMI tools

§ IMEI tools help to create application that interacts over the web or the network which consist rmi and rmi registry.

Ø Security tools

§ Security tools help you to set security policy on your system and create application that can work within the scope of the security policy which consists of the CI tools Jaya signature policy tools extra.

Ø Java development tools

§ Development tools used for development of the JAVA application and web application it provides a complete UI for development environment which consists NetBeans eclipse etc.

Ø Java Web service tools

§ Web service tools provide Java architecture for building web application and parsing XML data from one site to another site.

Ø Java scripting tools

§ Java scripting tools enable user to run external programming on the Java Platform it might not be available in the JDK version means it install separately.

Ø Java troubleshooting tools

§ Troubleshooting can be used for understand a task that may generate error at runtime as well as in a future.

9. A Write a First Simple Java Program and Explain the process of Compiling and Executing Java Program:

· Java is an Object Oriented and Platform Independent Programming Language.

· Basically a "Hello, World!" is a simple program in any programming language that simply prints Hello, World! on the output screen.

The requirement for Java Hello World Example:

ü For executing any Java program, the following software or application must be properly installed: -

· Install the JDK if you don't have installed it, than first download the JDK and install it.

· Set path of the jdk/bin directory.

· Create the Java program.

· Compile and run the Java program.

Let's create the hello java program:

class Simple

{

public static void main (String args [])

{

System.out.println("Hello World");

}

1. Now Save the above file as Simple.java

2. Compile file with following command: -

>>javac Simple.java

3. Execute file with following command: -

>>java Simple

Ø The Output will be:

Hello World

· When we compile Java program using javac tool, the Java compiler converts the source code into byte code.

Parameters used in First Java Program

· class keyword is used to declare a class in Java.

· public keyword is an access modifier that represents visibility. It means it is visible to all.

· static is a keyword. If we declare any method as static, it is known as the static method. The core advantage of the static method is that there is no need to create an object to invoke the static method. The main() method is executed by the JVM, so it doesn't require creating an object to invoke the main() method. So, it saves memory.

· void is the return type of the method. It means it doesn't return any value.

· main represents the starting point of the program.

· String[] args or String args[] is used for command line argument. System.out.println() is used to print statement. Here, System is a class, out is an object of the PrintStream class and println () is a method of the PrintStream class.

10. Explain Java Data types:

· Every variable has data type.

· Data type define that which type of value are stored in variable and it also define the size of a different data type.

1. Primitive data types: The primitive data types include boolean, char, byte, short, int, long, float and double.

2. Non-primitive data types: The non-primitive data types include Classes, Interfaces, and Arrays.

Primitive data types:

· Primitive data types specify the size and type of variable values. Following are primitive data types:

1. Boolean type – Boolean:

· A boolean data type can store either True or False. They can be used to check whether two values are equal or not (basically in conditional statements to return True or False).

· Typically, it is used as a flag variable to track true or false conditions.

· The default boolean value is False.

· The default boolean size is 1 bit.

2. Character type – char

· The char data type stores a single character.

· It stores both lower case and upper case characters which must be enclosed in single quotes.

· It takes memory space of 16 bits or 2 bytes. The values stored range between 0 to 65536.

3. Integer type – int

· An integer type stores an integer number with no decimal value.

· There are four integer types in Java – byte, short, int, and long.

· The default Integer value is 0.

· The default Integer size is 4 bytes.

4. Byte

· The byte data type is used to save memory in large arrays where the memory savings is most required.

· It saves space because a byte is 4 times smaller than an integer.

· It can also be used in place of "int" data type.

· It is an 8-bit signed and value-range lies between -128 to 127 . Its minimum value is -128 and maximum value is 127. Its default value is 0.

5. Short

· Short is a 16-bit signed two’s complement integer. It stores whole numbers with values ranging from -32768 to 32767.

· Its default value is 0.

· The short data type can also be used to save memory just like byte data type.

· A short data type is 2 times smaller than an integer.

6. Float

· It is a floating-point data type that stores the values including their decimal precision.

· It is not used for precise data such as currency or research data.

Ø A Float value:

· is a single-precision 32-bit or 4 bytes IEEE 754 floating-point.

· can have a 7-digit decimal precision.

· ends with an ‘f’ or ‘F’.

· default value = 0.0f.

· stores fractional numbers ranging from 3.4e-038 to 3.4e+038.

7. Double

· The double data type is similar to float.

· The difference between the two is that is double twice the float in the case of decimal precision.

· It is used for decimal values just like float and should not be used for precise values.

Ø A double value:

· is a double-precision 64-bit or 8 bytes IEEE 754 floating-point.

· can have a 15-digit decimal precision.

· default value = 0.0d.

· stores fractional numbers ranging from 1.7e-308 to 1.7e+308.

Non-Primitive Data Types

· Non-Primitive datatype cannot store the value of a variable directly in memory.

· They store a memory address of the variable. Unlike primitive data types, which are defined by Java, non-primitive data types are user-defined.

· They are created by programmers and can be assigned with null. All non-primitive data types are of equal size.

1. Array

· An array is used to hold elements of the same type.

· It is an object in java, and the array name (used for declaration) is a reference value that carries the base address of the continuous location of elements of an array.

2. Class

· A class is a user-defined data type from which objects are created.

· It describes the set of properties or methods that are common to all objects of the same type.

· It contains fields and methods that represent the behaviour of an object.

· A class gets invoked by the creation of the respective object.

3. Interface

· An interface is declared like a class.

· The key difference is that the interface contains methods that are abstract by default;

· It cannot have a method body.

11. Explain Java Tokens

· The tokens are the small building blocks of a Java program that are meaningful to the Java compiler.

· This token defines the structure of Java language when you submit the Java program to Java compiler.

· Tokens can be classified as follows:

1. Keyword

2. Literal

3. Identifier

4. Whitespace

5. Separators

6. Comments

7. Operators

Keywords

· These are the pre-defined reserved words of any programming language.

· Each keyword has a special meaning.

· It is always written in lower case.

· Java provides the following keywords:

Literal

· Constant in Java are call literal entity they do not change their value in a program during its execution are call literal integer.

· Literal in a java roll number there are three types of integer literal that is a decimal octal and hexadecimal.

· A number with decimal point and fractional value are call floating-point literal floating point literal are represented in one of the two forms that are standard and scientific.

· Character literal in Java are single character literal Java support a set of characters’ literal are also known as escape sequence which cannot be printed like \n \t etc...

· It sends a sequence of character in a paragraph or double Kota is a continue as string literal.

Identifier

· Identifiers are used to name a variable, constant, function, class, and array.

· It usually defined by the user.

· It uses letters, underscores, or a dollar sign as the first character.

· Remember that the identifier name must be different from the reserved keywords. There are some rules to declare identifiers are:

· The first letter of an identifier must be a letter, underscore or a dollar sign. It cannot start with digits but may contain digits.

· The whitespace cannot be included in the identifier.

· Identifiers are case sensitive.

White space

· Java is a free from language this means that you do not need to follow any specially rules for example if you return a Java Program in a single line not in a structure there after you tell how to execute and run as a console application in a java whitespaces space tab and newline

Separators

· The separators in Java is also known as punctuators.

· There are nine separators in Java, are as follows:

· separator <= ; | , . ( ) { } [ ]

Comments

· Comments allow us to specify information about the program inside our Java code.

· Java compiler cannot read the portion to be commented.

· The Java compiler treats comments as whitespaces.

· Java provides the following two types of comments:

· Line Oriented: It begins with a pair of forwarding slashes (//).

· Block-Oriented: It begins with /* and continues until it founds */.

Operators

· In programming, operators are the special symbol that tells the compiler to perform a special operation.

· Java provides different types of operators that can be classified according to the functionality they provide.

· There are eight types of operators in Java, are as follows:

1. Arithmetic Operators

2. Assignment Operators

3. Relational Operators

4. Unary Operators

5. Logical Operators

6. Ternary Operators

7. Bitwise Operators

8. Shift Operators

Operator	Symbols
Arithmetic	+ , - , / , * , %
Assignment	= , += , -= , *= , /= , %= , ^=
Relational	==, != , < , >, <= , >=
Unary	++ , - - , !
Logical	&& , \|\|
Ternary	(Condition) ? (Statement1) : (Statement2);
Bitwise	& , \| , ^ , ~
Shift	<< , >>

Arithmetic Operators:

• They are used to perform simple arithmetic operations on primitive data types. * : Multiplication

• / : Division

• % : Modulo

• + : Addition

• – : Subtraction

Relational Operators:

• These operators are used to check for relations like equality, greater than, less than. They return boolean result after the comparison and are extensively used in looping statements as well as conditional if else statements. General format is,

• ==, Equal to : returns true if left hand side is equal to right hand side.

• !=, Not equalto: returns true if left hand side is not equal to right hand side.

• <, less than: returns true if left hand side is less than right hand side.

• <=, less than or equal to: returns true if left hand side is less than or equal to right hand side.

• >, Greater than: returns true if left hand side is greater than right hand side.

• >=, Greater than or equal to: returns true if left hand side is greater than or equal to right hand side.

Logical Operators:

• These operators are used to perform “logical AND” and “logical OR” operation, i.e. the function similar to AND gate and OR gate in digital electronics.

• One thing to keep in mind is the second condition is not evaluated if the first one is false, i.e. it has a short-circuiting effect. Used extensively to test for several conditions for making a decision.

• &&, Logical AND: returns true when both conditions are true.

• ||, Logical OR: returns true if at least one condition is true.

• !, Logical NOT: returns true when a condition is false.

Bitwise Operators:

• These operators are used to perform manipulation of individual bits of a number. They can be used with any of the integer types. They are used when performing update and query operations of Binary indexed tree.

• &, bitwise AND operator: returns bit by bit AND of input values.

• |, Bitwise OR operator: returns bit by bit OR of input values.

• ^, Bitwise XOR operator: returns bit-by-bit XOR of input values.

• ~, Bitwise Complement Operator: This is a unary operator, which returns the one’s compliment representation of the input value, i.e. with all bits inversed.

Assignment Operator:

• ‘=’ Assignment operator is used to assign a value to any variable. It has a right to left associativity, i.e value given on right hand side of operator is assigned to the variable on the left and therefore right hand side value must be declared before using it or should be a constant.

Unary Operators :

• Unary operators need only one operand. They are used to increment or decrement a value.

• (–) :Unary minus, used for negating the values.

• (+) : Unary plus, used for giving positive values. Only used when deliberately converting a negative value to positive.

• (++) : Increment operator, used for incrementing the value by 1. There are two varieties of increment operator.

i. Post-Increment: Value is first used for computing the result and then incremented.

ii. Pre-Increment: Value is incremented first and then result is computed.

• (- -) : Decrement operator, used for decrementing the value by 1. There are two varieties of decrement operator.

i. Post-Decrement: Value is first used for computing the result and then decremented.

ii. Pre-Decrement: Value is decremented first and then result is computed.

Shift Operators:

• These operators are used to shift the bits of a number left or right thereby multiplying or dividing the number by two respectively. They can be used when we have to multiply or divide a number by two. General format-

• <<, Left shift operator: shifts the bits of the number to the left and fills 0 on voids left as a result. Similar effect as of multiplying the number with some power of two.

• >>, Signed Right shift operator: shifts the bits of the number to the right and fills 0 on voids left as a result. The leftmost bit depends on the sign of initial number. Similar effect as of dividing the number with some power of two.

• The dot (.) operator is used to select members of a class or object instance:

• The new operator is used to create objects out of a class.

12. Explain Type Casting: -

• In Java, type casting is a method or process that converts a data type into another data type in both ways manually and automatically.

• The automatic conversion is done by the compiler.

• And manual conversion performed by the programmer.

• There are two types of type casting:

1. Widening Type Casting.

2. Narrowing Type Casting.

Widening Type Casting:

• Converting a lower data type into a higher one is called widening type casting.

• It is also known as implicit conversion or casting down.

• It is done automatically.

• It is safe because there is no chance to lose data.

It takes place when:

• Both data types must be compatible with each other.

• The target type must be larger than the source type.

• For Example: -

Ø byte -> short -> char -> int -> long -> float -> double.

Narrowing Type Casting

• Converting a higher data type into a lower one is called narrowing type casting.

• It is also known as explicit conversion or casting up.

• It is done manually by the programmer.

• If we do not perform casting, then the compiler reports a compile-time error.

• We can represent flow of narrowing type casting as follow: -

double -> float -> long -> int -> char -> short -> byte.

13. Explain Decision Statements in Java:

• Conditional statements are used to perform different actions based on various conditions.

• Java supports two types of selection statements: if and switch.

• These statements allow us to regulate the flow of our program’s execution.

The if-else statement:

• The if-else statement is used to carry out a logical test and then take one of two possible actions depending on the outcome of the test (i.e. whether the outcome is true or false).

• The else position of the if-else statement is optional. Thus, in its simplest general form, the statement can be written.

if(expression)
{
statement;
}

• The expression must be placed in parenthesis, as shown. In this form, the statement will be executed only if the expression has non-zero value (i.e. true).

• If the expression has a value of zero (i.e. expression is false), then the statement will be ignored.

• The statement can be either simple or compound. In practice, it is often compound statement, which may include other control statements.

• The general form of an if statement which include the else clause is: -

if (expression)

{
statement1;
}
else
{
statement2;
}

• If the expression has a non-zero value, then statement 1 will be executed.

• Otherwise, (i.e. expression is false), statement 2 will be executed.

• It is possible to next if…else statement within one-another, just as we did with loops, there are several different forms that nested if…else two-layer nesting is:

• In this situation, one can complete if… else statement will be executed if expression is nonzero (true) and another complete if else statement will be executed if expression is false (zero).

• It is of course, possible that statement 1, statement2, statement3 and statement4 will contain another if…else statements. We would then have multi-layer nesting.

Switch Case Statement:

• The switch case statement provides and alternative way to tack decision it is work on user choice.

• It means it provide a way by which user can tack them on decision.

• It is not a logic but provide powerful structure to maintain more than one logic in it.

• Switch case statement tack an integer expiration for execute a specific block.

• In switch case statement each case is prated label.

• Switch statement have a default option if none of the expiration match with any case than it executes default case.

• Following is a syntax of switch case statement.

Switch (expression)

{

Case 1:

Statement;

Break;

Case 2:

Statement;

Break;

Default:

Statement;

}

• According to the syntax switch is reserve keyboard and it contain expression in character or in int type data

• All the case is containing within two curly bracket and each case has separate label.

• Switch case statement contain break in every case statement to stop execution of switch case after maintain their desire case.

• Default case statement does not require break statement because it always written at last in switch case block.

14. Explain Looping Statements in Java:

• In Java, there are three types of loops.

1. for loop

2. while loop

3. do...while loop

Java for Loop:

• Java for loop is used to run a block of code for a certain number of times. The syntax of for loop is:

• For Loop is the example of Entry controlled loop.

for (initialization; condition; increment/decrement) {

// body of the loop

}

• The execution of the for statement is as follows:

1. Initialization of the control variables is done first, using assignments statement such as i=0 and count=0. The variables i and count are known as loop controls.

2. The value of the control variables is tested using the test condition. The test condition is relational expression, such as i>0 or i<10 that determines when the loop is terminated and the execution continues with statement that immediately follow by the loop.

3. When the body of the loop is executed, the control is transferred back to the for statement either evaluating the last statement is the loop.

• Now, the control variable is incremented using and assignment statement such as i=i+1 and if the new value of the control is satisfied under test condition, then the body of the loop is executed.

• This process continues till the value of the control variable fails to satisfy the test-condition.

While statement:

• The while statement is used to carry out looping operations. The general form of the statements.

• While Loop is the example of Entry controlled loop.

initialization;
while(exp)
{
    statement1;
    statement2;
    increment/decrement;
}

• The enclose statements within two braces will be executed repeatedly as long as the expression evaluated as true.

• When the expression is evaluating a false or when condition will be false then it will come out from the loop and stop the execution of that loop.

• Initialization statement initialize some memory variable with some value.

• Increment or decrement operator increase or decrease the value of operator is use by expression.

Java do...while loop

• The do...while loop is similar to while loop.

• However, the body of do...while loop is executed once before the test expression is checked. For example,

do
{
    statement1;
    statement2;
    increment/decrement;
} while (exp);

• The enclosed statement within two braces will be executed repeatedly as the value of expression is not zero.

• Notice that statement will always be executed at least once.

• Since the test for repetition does not occur until the end of the first, pass through the loop.

15. Explain Jumping Statements in Java:

• Jumping statements are control statements that transfer execution control from one point to another point in the program. There are two Jump statements that are provided in the Java programming language:

1. Break statement.

2. Continue statement.

3. Return

Break statement

• In java, the break statement is used to terminate the execution of the nearest looping statement or switch statement. The break statement is widely used with the switch statement, for loop, while loop, do-while loop.

Following is a Syntax to declare break statement:

   break;

• When a break statement is found inside a loop.

• The break statement is written simply as break; without any embedded expressions or statement. For example :

   for (i=1; i<=10; i++)

               if(i==5) {

                           break;

                           printf(“\ni=%d”,i);

• The output will be 1,2,3,4 and then break will terminate this loop and stop the execution of the for loop.

Continue statement

• The continue statement is used to skip or to bypass some step or iteration of looping structure. It does not terminate the loop but just skip or bypass the particular sequence of the loop structure. It is simply written as continue.

for(i=1; i<=10; i++)

               if(i==5) {

                           continue;

                           printf(“\ni=%d”,i);

• The output of the above program will be 1,2,3,4,6,7,8,9,10. The 5^thiteration of the loop will be skipped as we have defined the continue for that iteration. So it will not print the value ‘5’.

Return statement

• In Java programming, the return statement is used for returning a value when the execution of the block is completed.

• In Java, every method is declared with a return type such as int, float, double, string, etc.

• These return types required a return statement at the end of the method. A return keyword is used for returning the resulted value.

• The void return type does not require any return statement. If we try to return a value from a void method, the compiler shows an error.

• The syntax of a return statement is the return keyword is followed by the value to be returned.

return return_value

According to above, return is keyword and return value is value return by the return keyword.

16. Explain Array in Java:

• An array is a fixed size of sequential collection of element of same data type.

• Array is also known as collection of same data type element.

• It is a simple looping of data type it.

• It is used to represent a list of numbers or a list of names.

• It is one of the data structure of Java.

• Individual values of an array are callan element.

• Array is refer to use as a derived data type.

• Array is define as a set of homogenous data item.

• It provide ability to use a signal name to represent collection of items and refer to an item by the specific item index.

• Java support following different type of array.

1. One Dimensional Array

2. Multi-Dimensional Array

3. Jagged Array

• Array is a collection of similar type element that have same name.

One Dimensional Array:

• In a one-dimensionalarray, a list of item can be given a variable name using only one subscript operator and such a variable is called signal dimensional array.

• Following is general syntax of one-dimensional array.

• int []a = new int [10];

• data_type [ ] variable_name = new data_type[size] ;

• According to above syntax data type may be any valid primitive or non-primitive type

• Variable name must be in a valid form and using subscript operator we can define a size of an array and It must be in whole number.

• For example: if you want to represent a set of five integer number than it can be declare as int []a = new int[5];

• One thing to be noted that the subscript of an array is start always with 0(zero).

• To access the element of an array in a program use any valid looping structure.

• Java also allow to assign initial value of an element which is declare in an array.

• Like int [ ]a=new int[5]{1,2,3,4,5};

• The list of initial value must be enclosed within two curly brackets and value are separated by comma it’s also called compile time initialization.

• According to above example array can be initialize at compile time which can be describe as follow.

• a[0] = 1

• a[1] = 2

• a[2] = 3

• a[3] = 4

• a[4] = 5

• According to above example array can also be define with any other valid data type.

Multi-Dimensional Array:

• In a two dimensional array a list of item can be given a variable name using only two subscript operator and such a variable is called two dimensional array.

• Following is general syntax of two dimensional array.

• int [ ][ ]a = new int[3][3];

• Data_type [ ][ ] variable_name = new data_type[row size][column size];

• According to above syntax data type may be any valid primitive or non-primitive type.

• Variable name must be in a valid form and using subscript operator we can define a row and column size of an array and It must be in an whole number.

• For example: if you must be in an whole number a set of 3*3 integer number than it can be declare as

• int [ ][ ]a = new int [3][3];

• One thing to be noted that the subscript of an array is start with zero.

• To access the element of an array in a program use any valid nested looping structure.

• Java also allow to assign initial value of an element which is declare in an array.

• int int [ ][ ]a = new int [3][3] {{1,2,3},{4,5,6},{7,8,9}};

• The list of initial value most be enclose within two curly brackets and value are separated by comma.

• It’s also called compile time initiation.

1	2	3
4	5	6
7	8	9

• According to above example array can be initialize at compile time which can be describe as

• According to above example array can also be define with float character or any other valid data type.

Jagged Array:

• A jagged array is an array of arrays such that member arrays can be of different sizes, i.e., we can create a 2-D array but with a variable number of columns in each row.

• In other words, the length of each array index can differ.

• The elements of Jagged Array are reference types and initialized to null by default.

• Jagged Array can also be mixed with multidimensional arrays.

• Here, the number of rows will be fixed at the declaration time, but you can vary the number of columns.

• data_type[][] name_of_array = new data_type[rows][]

• According to above syntax data type may be any valid primitive or non-primitive type.

• Variable name must be in a valid form and using subscript operator we can define only row size because column size may be variable of an array and It must be in an whole number.

• For example: if you must be in an whole number a set of 3*3 integer number than it can be declare as

• int [ ][ ]a = new int [3][];

• One thing to be noted that the subscript of an array is start with zero.

• To access the element of an array in a program use any valid nested looping structure.

• Java also allow assigning initial value of an element, which is declare in an array.

• int [ ][ ]a = new int [ ][ ] {{1,2},{3,4,5,6},{7,8,9}};

• The list of initial value most be enclose within two curly brackets and value are separated by comma.

• It is also called compile time initiation.

• According to above example array can be initialize at compile time which can be describe as

• According to above example array can also be define any other valid data type.

17. Explain Command Line Argument:

• The java command-line argument is an argument i.e. passed at the time of running the java program.

• The arguments passed from the console can be received in the java program and it can be used as an input.

• So, it provides a convenient way to check the behavior of the program for the different values.

• You can pass N numbers of arguments from the command prompt

• When command line arguments are supplied to JVM, JVM wraps these and supply to args[].

• It can be confirmed that they are actually wrapped up in args array by checking the length of args using args.length

• Following is an example of command line Argument…

class Cmd

{

public static void main(String args[])

{

System.out.println("Your first argument is: "+args[0]);

}

18. Explain OOP Concept:

• OOP stands for Object Oriented Programming Language.

• Object means a real-world entity such as a pen, chair, table, computer, watch, etc.

• Object-Oriented Programming is a methodology or paradigm to design a program using classes and objects.

• OOP concepts are as follows:

1. Class

2. Object

3. Encapsulation

4. Inheritance

5. Polymorphism

Class:

• Class is a collection of data member and data function

• Class is a template that define the form of an object

• Class is an implementation of encaptulization concept of OOP

• Class is nothing but one kind of structure of data binding

• Class is user defined data type we can use class in a main function or in any event using an object

• Object is a variable or instance of the class

• We can create as many instance of class as we want

• Usually with the help of class we define a big project in a small part class make modification and improvements of large and complex program

• Usually we create data member as a private and member functions are public but it is not compulsory

• Class contains constructor destructor nested class methods etc…

Object:

• Object is key to understand object oriented Technology.

• An object is an entity that has state and behavior.

• It can be physical or logical tangible or intangible.

• Following is some characteristics of an object.

• State : State the present data value of an object.

• Behaviour : Present behaviour or a functionality of an object such as amount deposit in a bank and withdraw from the bank.

• Identity : Object identity is typically implemented using an unique ID the value of the ID is not visible to the external user heat is used internally by the system to identify each object uniquely.

• For example Pen is an object its name is Synosoft and its color is a blue it is known as a state and it is used to write something so writing is its behaviour object is an instance of a class.

• Class is a blueprint or template from which object are created so, the object is an instance of a class.

Encapsulation:

• Encapsulation is an object oriented programming based concept.

• Encapsulation protect important data inside the class.

• Which we do not want to be exposed outside the class.

• Encapsulation process means binding the Data Member and Member function in single unit.

• Data member means variable property etc... while the Member function means method and the class is one of the best example of an encapsulation.

• Encapsulation hide private or unwanted data from outside the class.

• With the Encapsulation we can make variable property and method to private.

Inheritance:

• Inheritance is a mechanism in which one class acquire all the properties and behaviour of another parent class.

• The idea behind Inheritance is just you create a new class that are built upon an existing class.

• When you inherit from an existing class you can reuse method and field of parent class you can add new method and field also.

• Inheritance represent “is a” relationship.

• It is also known as parent child relationship.

• Inheritance also known as generalization.

• Java use extend keyword to create inheritance.

• The main advantages of inheritance: -

• Reusability.

• Save time.

• Help in modularization of code.

Polymorphism:

• Polymorphism is a concept by which we can perform a single action by different ways

• Polymorphism is derived from Greek word where poly means many and morphism means forms,

• So polymorphism means many forms there are two types of polymorphism in Java

• Compile time polymorphism

• Runtime polymorphism

• We can perform polymorphism in Java by method overloading and overriding

• If overload static method in java it is the example of compile time polymorphism

• While the runtime polymorphism are the dynamic method, dispatch is a process in which a call to an overloading is resolved at runtime rather than Compile time.

• In this process overriding method is call to the reference variable of a superclass

• The determination of the method to be call is based on object being referred by the reference variable

• Polymorphism can be static or dynamic

• In a static polymorphism response to a function is determined at the compile time and the dynamic polymorphism is decided at runtime

• The static polymorphism linking function with an object during compile time is called early binding it is call Static Binding

• In a dynamic polymorphism, you have to create abstract class that used to provide partial class implementation of an interface.

• Implementation is a completed when derived class inherit from it

Abstract class contain abstract method, which are implemented by derived class.

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OOP Using Java for IMCA, BCA, MCA & all IT Students

Following is a Syntax to declare break statement:

Encapsulation:

Inheritance:

Polymorphism: