OOPs and Its Concepts in Java
Brief Introduction to OOP
Object Oriented Programming or OOP is the technique to create programs based on the real world. Unlike procedural programming, here in the OOP programming model programs are organized around objects and data rather than actions and logic. Objects represent some concepts or things and like any other objects in the real Objects in programming language have certain behavior, properties, type, and identity. In OOP based language the principal aim is to find out the objects to manipulate and their relation between each other. OOP offers greater flexibility and compatibility and is popular in developing larger application. Another important work in OOP is to classify objects into different types according to their properties and behavior. So OOP based software application development includes the analysis of the problem, preparing a solution, coding and finally its maintenance.
Java is a object oriented programming and to understand the functionality of OOP in Java, we first need to understand several fundamentals related to objects. These include class, method, inheritance, encapsulation, abstraction, polymorphism etc.
Class - It is the central point of OOP and that contains data and codes with behavior. In Java everything happens within class and it describes a set of objects with common behavior. The class definition describes all the properties, behavior, and identity of objects present within that class. As far as types of classes are concerned, there are predefined classes in languages like C++ and Pascal. But in Java one can define his/her own types with data and code.
Object - Objects are the basic unit of object orientation with behavior, identity. As we mentioned above, these are part of a class but are not the same. An object is expressed by the variable and methods within the objects. Again these variables and methods are distinguished from each other as instant variables, instant methods and class variable and class methods.
Methods - We know that a class can define both attributes and behaviors. Again attributes are defined by variables and behaviors are represented by methods. In other words, methods define the abilities of an object.
Inheritance - This is the mechanism of organizing and structuring software program. Though objects are distinguished from each other by some additional features but there are objects that share certain things common. In object oriented programming classes can inherit some common behavior and state from others. Inheritance in OOP allows to define a general class and later to organize some other classes simply adding some details with the old class definition. This saves work as the special class inherits all the properties of the old general class and as a programmer you only require the new features. This helps in a better data analysis, accurate coding and reduces development time.
Abstraction - The process of abstraction in Java is used to hide certain details and only show the essential features of the object. In other words, it deals with the outside view of an object (interface).
Encapsulation - This is an important programming concept that assists in separating an object's state from its behavior. This helps in hiding an object's data describing its state from any further modification by external component. In Java there are four different terms used for hiding data constructs and these are public, private, protected and package. As we know an object can associated with data with predefined classes and in any application an object can know about the data it needs to know about. So any unnecessary data are not required by an object can be hidden by this process. It can also be termed as information hiding that prohibits outsiders in seeing the inside of an object in which abstraction is implemented.
Polymorphism - It describes the ability of the object in belonging to different types with specific behavior of each type. So by using this, one object can be treated like another and in this way it can create and define multiple level of interface. Here the programmers need not have to know the exact type of object in advance and this is being implemented at runtime.
Java Examples
Exception Handling in Example
Exception, that means exceptional errors. Actually exceptions are used for handling errors in programs that occurs during the program execution.
Java Exception - Exception Handling in Java
Exception, that means exceptional errors. Actually exceptions are used for handling errors in programs that occurs during the program execution. During the program execution if any error occurs and you want to print your own message or the system message about the error then you write the part of the program which generate the error in the try{} block and catch the errors using catch() block. Exception turns the direction of normal flow of the program control and send to the related catch() block. Error that occurs during the program execution generate a specific object which has the information about the errors occurred in the program.
In the following example code you will see that how the exception handling can be done in java program. This example reads two integer numbers for the variables a and b. If you enter any other character except number ( 0 - 9 ) then the error is caught by NumberFormatException object. After thatex.getMessage() prints the information about the error occurring causes.
Code of the program :
| import java.io.*;
public class exceptionHandle{
public static void main(String[] args) throws Exception{
try{
int a,b;
BufferedReader in =
new BufferedReader(new InputStreamReader(System.in));
a = Integer.parseInt(in.readLine());
b = Integer.parseInt(in.readLine());
}
catch(NumberFormatException ex){
System.out.println(ex.getMessage()
+ " is not a numeric value.");
System.exit(0);
}
}
}
|
- Java Identifier Example
In this example you will learn what is identifier and primitive data type of a identifier. This tutorials will teach you how to use these identifier in you java programming.
Java - Identifier and Primitive Data Types in java
In this example you will learn what isidentifier and primitive data types of a identifier. This tutorials will teach you how to use these identifier in you java programming. Identifier is is a simple variable name which is defined as the value container. The type of value stored by identifier is defined by the special java keyword is termed as primitive data type.
In the given example there are some identifiers have been used like byteident, shortident, intident, longident, charident, stringident, floatident, doubleident. And there are some primitive data types of used identifiers have been also used in the program like byte, short, int, long, float, double, char andString.
All the data type has it's own capacity to keep the maximum value. Which have been mentioned below :
| Primitive Data Types |
| Keyword | Description | Size/Format |
| Integers |
| byte
| Byte-length integer | 8-bit two's complement |
| short
| Short integer | 16-bit two's complement |
| int
| Integer | 32-bit two's complement |
| long
| Long integer | 64-bit two's complement |
| Real numbers |
| float
| Single-precision floating point | 32-bit IEEE 754 |
| double
| Double-precision floating point | 64-bit IEEE 754 |
| Other types |
| char
| A single character | 16-bit Unicode character |
| boolean
| A boolean value (true or false) | true or false |
Code of the Program :
public class identifierandpdatatype{
public static void main(String[] args){
byte byteident = 3;
short shortident=100;
int intident = 10;
long longident = 40000;
char charident = 'a';
String stringident = "chandan";
float floatident = 12.0045f;
double doubleident = 2333333.000000000033343343434f;
System.out.println(byteident + " is the value of identifire
named 'byteident' which primitive data type is byte.");
System.out.println(shortident + " is the value of
identifire named 'shortident' which primitive data type is short.");
System.out.println(intident + " is the value
of identifire named 'intident' which primitive data type is int.");
System.out.println(longident + " is the value
of identifire named 'longident' which primitive data type is long.");
System.out.println(charident + " is the value
of identifire named 'charident' which primitive data type is char.");
System.out.println(stringident + " is the value
of identifire named 'stringident' which primitive data type is string.");
System.out.println(floatident + " is the value
of identifire named 'floatident' which primitive data type is float.");
System.out.println(doubleident + " is the value
of identifire named 'doubleident' which primitive data type is double.");
}
}
|
- Java - Variable, Constant and Literal in Java
Variable : You can assign the values to the variable once it has been declared. The values of the variable can be changed anywhere in the program if the variable is accessible in that scope. In this example we have used the variable intvariable to illustrate this.
Java - Variable, Constant and Literal in Java
Posted on: June 4, 2007 at 12:00 AM
In this example you will see that how you can use variables, constants and literals in your program easily.
Java - Variable, Constant and Literal in Java
In this example you will see that how you can use variables, constants and literals in your program easily.
Variable : You can assign the values to the variable once it has been declared. The values of the variable can be changed anywhere in the program if the variable is accessible in that scope. In this example we have used the variable intvariable to illustrate this.
Constants: Constants are declared using the final keyword. The values of the constant can't be changed once its declared.
Literal : literal is an explicit number or string constant used in Java programs. This specifies the syntax of your declaration of different types of values and operations. That mean literal is totally based on the syntax. Whenever you want to show the message with java special symbols then you have to use the literals. For example to show the message "Directory of this file : c:\code\varconstltr.java" then you can write as shown below
System.out.println("Directory of this file : c:\\code\\varconstltr.java");
There are three type of literals : Numeric Literals, Char type Literals, String Literals as follows.
Code of the Program :
public class varconstltr{
public static final int constint=5;
public static void main(String[] args){
int intvariable;
for (int i = 0;i <= 10;i++){
intvariable = i;
System.out.println("All the values are : \n intvariable = "
+ intvariable + "\nconstint = " + constint);
}
System.out.println("Directory of this file : c:\\code\\varconstltr.java");
}
}
|
- Java Read File Example
In the section of Java Tutorial you will learn how to write java program to read file line by line. We will use the DataInputStream class to Read text File Line by Line.
- Copy file Example
This example illustrates how to copy contents from one file to another file. This topic is related to the I/O (input/output) of java.io package.
- Java Write to File Example
In the section of Java Tutorial you will learn how to write java program to write to a file.
- Java Create Directory Example
In the section of Java Tutorial you will learn how to write java program to create directory.
- Deleting Directory or File
This example illustrates how to delete the specified file or directory after checking weather the file exists or not. This topic is related to the I/O (input/output) of java.io package.
- Java Directory Listing Example
This example illustrates how to list files and folders present in the specified directory. This topic is related to the I/O (input/output) of java.io package.
- Java Word Count Example
This example illustrates how to count the number of lines, number of words and number of characters in the specified file. Program takes the file name as parameter and it counts the number of words and lines present in the file.
- Applet Example in Java
Applet is a program provided by java which is designed for execution within the web browser. Applets are mostly used for a small internet and intranet applications because of small size and it's compatibility among almost all web browsers.
- Boolean Expression in Java
In this example you will see that how the expression returns a boolean value which is either true or false. This example illustrates you how to make a boolean expression by using relational operators and how to use the returned value of the expression.
- Math Class Example
In this example you will learn about Math class. This example explains how you can use functions provided by the Math class like E, PI, round, abs, ceil, exp, floor, IEEEremainder, max,min, pow, random, rint, sqrt etc. to manipulate the mathematical operation in your program.
- String Buffer Example
In this example you will learn about StringBuffer class. This example explains how you can use functions provided by the StringBuffer class like append, insert, reverse, setCharAt, charAt, length, deleteCharAt, substring, delete, capacity etc. to manipulate the string operation in your program.
- Type Casting Example
This example illustrates that what is type casting? Type Casting refers to changing an entity of one datatype into another. This is important for the type conversion in developing any application.
- Java - Array in Java
Array: Array is the most important thing in any programming language. By definition, array is the static memory allocation. It allocates the memory for the same data type in sequence. It contains multiple values of same types.
- Copying an array to another
In this tutorial, you will learn how to copy data from one array to another. Here, providing you an example with code and its explanation to given below.
- charAt() method in Java
In this section, you will get the detailed explanation about the charAt() method of String class. We are going for using charAt() method.
- length() method in Java
In this section, you will learn how to use length() method of the String class. We are going to using length() method.
- toUpperCase() Method In Java
Here, you will see the procedure of converting letters of the string in uppercase letter.
- String Array in Java
In this section, you will learn how to use string array in Java. Here, you will see how to declare a string array and the syntax for using in the program.
- Average of Array
In this section, we will learn how to get an average of array. For this, first of all we have to define a class name "ArrayAverage" that has double type array to contain some values.
- Matrix Example in Java
In Java tutorial, you will learn about array and matrix. An array is the collection of same data type values. If we create a variable of integer type then, the array of int can only store the int values.
- Sum of two Matrix
In this section, we are going to calculate the sum of two matrix and containing its rows and columns. See below for better understanding to this.
- Multiplication of two Matrix
This is a simple java program that teaches you for multiplying two matrix to each other. Here providing you Java source code with understanding the Java developing application program.
- Square Elements of Two Dimensional Array
This is a simple java program for implementing the two dimensional array program and its square. This session provide you the best explanation with mathematical operation.
- Check Even-Odd:-Example
Now, you have to learn about the syntax of If - Else construct. How the If - Else construct used to flow the program control as for as needed.
- Java - Break statement in java
Break: The break statement is used in many programming languages such as c, c++, java etc. Some times we need to exit from a loop before the completion of the loop then we use break
- Java - Continue statement in Java
Continue: The continue statement is used in many programming languages such as C, C++, java etc. Sometimes we do not need to execute some statements under the loop then we use the continue statement that stops the normal flow of the control and control returns to the loop without executing the statements written after the continue statement.
- Java - The switch construct in Java
Switch is the control statement in java which also turns the normal flow control of the program as per conditions. It works same as If-Else construct. This is the difference between Switch and If-Else construct that switch is used for reduce the if statements.
- Switch Statement example in Java
This is very simple Java program for implementing the switch statement. Here, you will learn how to use the switch statement in your java program for developing java application.
- While Loop
Loop is the control statement of any language in which whenever you want to perform the repetitious work then you use the Loop control statement.
- do-while Loop in Java
In some conditions in java, you need to run some statements and processes once at least. For that you have to use the do while loop in after that check the condition then we use the do-while loop statement.
- For Loop in Java
The for loop is the type of looping construct. It also works as while loop construct but it provide the initialization, condition and the increment is same written in the for construct.
- Java - Class, Object and Methods in Java
Class : Whatever we can see in this world all the things are a object. And all the objects are categorized in a special group. That group is termed as a class.
- Java - Constructor in java
Constructor is the method which name is same to the class. But there are many difference between the method (function) and the Constructor.
- Constructor Overloading in Java
Constructors are used to assign initial values to instance variables of the class. A default constructor with no arguments will be called automatically by the Java Virtual Machine (JVM).
- Use of "this" keyword in java
The keyword this is useful when you need to refer to instance of the class from its method.
- Java - Threads in Java
Thread is the feature of mostly languages including Java. Threads allow the program to perform multiple tasks simultaneously. Process speed can be increased by using threads because the thread can stop or suspend a specific running process and start or resume the suspended processes.
- Occurrences of elements in an Array
This section illustrates you how to calculate occurrences of elements in an array. Occurrences means, the how many times an element occurs in the array.
- Change the user input to integer
Isn't it a very tedious job to enter the values each time before the compilation in the method itself. Now if we want to enter an integer value after the compilation of a program and force the JVM to ask for an input, then we should use Integer.parseInt(string str) .
- Making Tokens of a String
We have to break a String into tokens as well as we will know how many tokens has been generated. That's what we are trying to do in this program.
- Array List Example in java
In this example we are going to show the use of java.util.ArrayList. We will be creatiing an object of ArrayList class and performs various operations like adding removing the objects.
- Converting a Filename to a URL
A file object is used to a give a filename. Creating the File object doesn't mean that a file exists. It may be that the does not exist. Suppose if the file exists, first of all we need to convert the file object in URL, for this we use a method toURL(). It returns a URL object and throwsMalformedException. After this we will convert this URL to a file object by using getFile()method. We will read this file by using BufferedReader object.
- Creating a temporary file
In this program we are going to make a temporary file, which will be deleted automatically by the garbage collector when the program ends.
- Example of Date class
We can use Date class to use current date. In this program we are creating a Date object and by using it we are going to display the current date and time. It implements Serializable, Cloneable, Comparable interfaces. Its known subclasses are Date, Time, Timestamp.
- Determining if two Filename paths refer to the same file.
This program is going to determine that the file name refers to the same file or not. What you need to do is to create two File object and pass the file name in the constructor of both the Fileclass. Now match both the file instances. It will return false if the file paths are not equal. To send the true value we first have to normalize both the paths, only after that it will return true.
- Determining if a Filename path is a file or a directory
You can solve this problem very easily. What you need to do, just create a File object and pass some file name or a directory in it.
- Determining if a File or Directory exist
This is a very simple problem. You just have to determine whether a file or directory exists or not. If it exists it returns true otherwise in the else condition, it retunes vice-versa.
- Forcing Updates to a File to the Disk
In this program we are going to update a file forcefully. Firstly we have to make an object ofOutputStream and pass a file name in which you want to update in the constructor of aFileOutputStream class. After that pass some data to the stream. The methods we are using in this class has already been discussed in other topics.
50. Link List Example in Java
In this example we are going to show the use of java.util.LinkedList class. You will be creating an object of link list class and performing various operation like adding and removing object.
51. Listing the File System Roots
In this example we will list out all the drives in the disk. this requires an array of File class where all the drives will get stored by using only one method.
52. Reading a File into a Byte Array
In this program we will read a file in the form of a byte array. We can do it very easily. Firstly we will create an object of File class and pass the name of the file which we want to read, in the constructor of File class. We will use DataInputStream to read primitive data types.
53. Implementing a Serializable Singleton
In Singeton classes only one instance will be created. We are going to serialize the class. This can be done very easily. What we need to do is to implement a java.io.Serializable interface. We will use a method of Serializable interface that is readResolve().
54. Example of Java Stack Program
Stack is like a bucket we you can enter objects and retrieve it. Here in the example describes the methods to prepare an example of Java stack program. The Stack class represents a last-in-first-out (LIFO) stack of objects. It extends class Vector and implements Cloneable, Collection, List, Serializable interfaces. We mostly use push and pop operations.
- Vector Example in java
In this example we are going to show the use of java.util.Vector class. We will be creating an object of Vector class and performs various operation like adding, removing etc. Vector class extends AbstractList and implements List, RandomAccess, Cloneable, Serializable. The size of a vector increase and decrease according to the program. Vector is synchronized.
- Calculating the checksum of a file/Adler32
Adler32: It is a error checking technique used to check the accuracy of data while transmitting it to the other end. Errors are checked while the data is transferring. This scheme is as reliable as CRC32, but it is much faster to compute.
- Calculating the Checksum of the file/CRC32
CRC: CRC means Cyclic Redundancy Check. It is a error checking technique used to check the accuracy of data while transmitting it to the other end. Errors are checked while the data is transferring. CRC performs some type of calculation before transmitting the data and send the result to the other end. The other end repeats the same operation before accepting the data. If both the devices get the result same, it means the transmission is error free.
- Compressing the file into GZIP format.
This example will help to understand the concepts of GZIP. GZIP compresses the actual size of data files. It is a file compression utility program which can be found very easily found on internet. Its resultant file will have a .gz extension. Its main advantage is that it provides excellent levels of compression. It can be used where you want to save the file in less available area. It will compress the file to the great extent. It is a part of java.util.zip package.
- Constructing a File Name path
This Java programming tutorial will teach you how you can construct a file name path. By using the constructing filename path it is possible to set dynamic path, which is helpful for mapping local file name with the actual path of the file.
- Use of Array in Java
This Java programming example will teach you the the concepts of arrays so that you can write a program on array by yourself. An array works a container object which can hold a values of same type. The length of an array is created when the array is going to be created. Arrays can be created in following ways. One way to create a array is by using new operator. e.g.. : a = new int[5];. It will create an array of type int which can store 5 integer values. The next way to define array is just same as we have defined an array in the program below. Array should be used, where you have to store multiple values of the same type. For example if we have to store months of the year then the better idea is to make an array of it.
- Example of static method
This Java programming example will teach you the way to define a static methods. In java we have two types of methods, instance methods and static methods. Static methods can't use any instance variables. The this keyword can't be used in a static methods. You can find it difficult to understand when to use a static method and when not to use. If you have a better understanding of the instance methods and static methods then you can know where to use instance method and static method.
- Uncompressing the file in the GZIP format.
This example will help you to understand the concepts of GZIP. Sometimes it happens that when you download a file or any PDF file you get it in compressed mode. This means that the file is compressed, but can't read it in compressed form so, it needs to be uncompressed. There are various uncompress ion utility program which can be found very easily found on internet. If you are uncompressing a PDF with the extension .gz, then its resultant file will have a .PDFextension. Its main advantage is that it will uncompress the PDF file so that you can be able to read it. This utility is a part of java.util.zip package which provides classes and methods to compress and decompress the file.
- Example of a instance variable
When a number of objects are created from the same class, the same copy of instance variable is provided to all. Remember, each time you call the instance the same old value is provided to you, not the updated one . In this program we are showing that how a instance variable is called in each instance, but the copy remains same irrespective the counter we have used in the constructor of a class. We can't call the non-static variable in a main method. If we try to call the non-static method in the main method then the compiler will prompt you that non-static variable cannot be referenced from a static context. We can call the non-static variable by the instance of the class.
- Example of a class variable (static variable)
This Java programming example will teach you how you can define the static class variable in a class. When a number of objects are created from the same class, each instance has its own copy of class variables. But this is not the case when it is declared as static static.
- Swapping of two numbers
This Java programming tutorial will teach you the methods for writing program to calculate swap of two numbers. Swapping is used where you want to interchange the values. This program will help you to increase your programming ability.
- Swap two any numbers (from Keyboard)
This is a simple Java Oriented language program. If you are newbie in Java programming then our tutorial and example are helpful for understanding Java programming in the simplest way.
- Calculating the checksum of a Byte Array by using Adler32
Adler32: It is a error checking technique used to check the accuracy of data while transmitting it to the other end. Errors are checked while the data is transferring. This scheme is as reliable asCRC32, but it is much faster to compute.The byte is an 8- bit signed primitive data type quantity. The minimum value the byte is -128 and maximum value is +128. It is signed because it can take both negative and positive value. The Byte class wraps a value of primitive type byte in an object. A object of type Byte contains a single field whose type is byte.
- Calculating the checksum of a Byte Array by using CRC32
CRC32: It is a error checking technique used to check the accuracy of data while transmitting it to the other end. Errors are checked while the data is transferring.
- Comparing the File Dates
This java example will help you to compare the dates of files. In java we have the option to compare two or more files. This is useful when we have to compare the files. Mostly it happens that after creating a file or a directory we forgets when it was made or last modified, and sometimes it becomes essential to know the exact date and time of creation. By this example you will be able to understand it.
- Getting a absolute path
To find a file or directory it is very necessary to know the path of the file or directory so that you can access it. If you know the path then it is very easy to work on it. Suppose a situation where a problem comes in front you where you don't know the path of the file, then what will you do. Then this problem can be solved by using a method getAbsolutePath(). The methodgetAbsolutePath() should be used where we don't know the exact path of the file.
- Making Tokens of a Java Source Code
If you are new in Java programming then our tutorials and examples will be helpful in understanding Java programming in the most simplest way. Here after reading this lesson, you will be able to break java program into tokens.
72. Add two big numbers
In this section, you will learn how to add two big numbers. For adding two numbers implement two big decimal numbers then apply the Sum() method that takes both numbers. 73. String Buffer insert and append example
In this section, you will learn how to insert StringBuffer and append data. The StringBuffer is a class that implements multiple sequence of characters. The following program construct a string buffer that has '0' capacity. 74. Character Comparison Example
In this section, you will learn how to compare characters in Java. The java.lang package provides a method for comparing two case sensitive strings. The compareTo() method compares two strings on the basis of Unicode of each character of the given strings. 75. Comparison character cases ignoring case sensitiveness in java
In this section, you will learn how to compare two strings ignoring case sensitiveness Java provides the method that ignores cases, it only compare the character's sequence. ThecompareToIgnoreCase() method compares two strings and ignores its cases. 76. Combine String example
In this section, you will learn how to combine or merge two strings in java. The java.langpackage provides the method that helps you to combine two strings and making into single string. Compare string example
In this section, you will learn how to compare two strings in java. The java lang package
