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Mastering Text File Reading in Java: Methods and Examples

Reading Text Files in Java: Different Methods

Welcome to the world of Java programming! Dealing with text files is one of the most common programming tasks that Java developers encounter. This article will explore the various ways in which you can read text files in Java, using different classes.

We will dive into the Scanner Class, BufferedReader Class, and the FileReader Class. Each of these classes has its own strengths and weaknesses, and by the end of this article, you will have a better understanding of their differences and how to use them in your programs.

Using Scanner Class to Read Text Files

The Scanner Class is a powerful class in Java that makes reading text files easy and efficient. One of the advantages of using Scanner is that it can handle almost all types of data types that are present in a text file.

This means that you do not have to worry about parsing the data from the text file because Scanner does it for you. To read a file using Scanner, we first have to create a File object that represents the file we want to read.

Heres an example:

File file = new File(“filename.txt”);

Scanner scanner = new Scanner(file);

In this example, we create a File object named file that points to the file we want to read. Then, we create a Scanner object named scanner that reads from the file.

Using BufferedReader Class to Read Text Files

The BufferedReader Class is another powerful class in Java that can be used to read text files. It works by reading a large chunk of data from the file into memory and then parsing it line by line.

One of the benefits of using BufferedReader is that it is generally faster than using Scanner in reading large files. Heres an example:

File file = new File(“filename.txt”);

FileReader fileReader = new FileReader(file);

BufferedReader bufferedReader = new BufferedReader(fileReader);

In this example, we create a File object that represents the file we want to read.

Then, we create a FileReader object that reads from the file. Finally, we create a BufferedReader object, which reads from the FileReader object.

Using FileReader Class to Read Text Files

The FileReader Class reads plain text files using the default character encoding of the operating system. It is useful when you are dealing with text files that are small.

Creating a FileReader object is straightforward, as it only requires the file path as an argument. Heres an example:

File file = new File(“filename.txt”);

FileReader fileReader = new FileReader(file);

In this example, we create a File object named file that points to the file we want to read.

Then, we create a FileReader object named fileReader that reads from the file.

Using hasNext() and nextLine() Functions

Now, lets move on to the common methods and functions that can be used to read text files. One of the most basic methods used by the Scanner Class is the hasNext() function.

This function returns a boolean value that tells us whether there are more tokens available to read. Tokens are simply the parts of the text that are separated by whitespace.

For example:

Scanner scanner = new Scanner(“Hello World!”);

boolean hasNext = scanner.hasNext();

In this example, we create a Scanner object that reads from the String “Hello World!”. Then, we check to see if there is more data to read using the hasNext() function.

Another useful method in reading text files using the Scanner Class is the nextLine() function. This function reads the next available line from the file.

Heres an example code snippet:

Scanner scanner = new Scanner(System.in);

System.out.println(“Enter your name: “);

String name = scanner.nextLine();

System.out.println(“Your name is ” + name);

In this example, we create a Scanner object that reads from the standard input. Then, we prompt the user to enter their name using the println() function.

We read the users input using the nextLine() function and store it in a variable named name.

Conclusion

In this article, we explored different approaches to reading text files in Java using the Scanner Class, BufferedReader Class, and the FileReader Class. We also looked at various methods and functions that can be used to parse data from the text file.

Hopefully, this article has provided you with a good starting point in reading and handling text files in Java.

3) Reading Text Files using InputStream and Scanner Class

The InputStream Class is an abstract class in the Java I/O package that provides the basic functionality for reading input. It can read data byte by byte, making it useful for reading binary data.

InputStreams are useful when reading data from network sockets, files, and other types of input sources.

Creating an InputStream Object

To use InputStream to read text files, we must first create an InputStream object that points to the file we want to read. Here’s how to create an InputStream object for a text file:

InputStream inputStream = new FileInputStream(“filename.txt”);

In this example, we create a FileInputStream object named ‘inputStream’ that reads from the file “filename.txt”.

Passing InputStream to Scanner Class

Once we have created the InputStream object, we can pass it to the Scanner class to parse data from the file. Here’s an example code snippet:

Scanner scanner = new Scanner(inputStream);

In this example, we create a Scanner object that reads from the InputStream object ‘inputStream’.

The Scanner class has built-in parsing ability that allows it to read data from various input sources, including InputStream objects. The combination of InputStream and Scanner classes provides a powerful tool for reading text files in Java.

4) Reading Text Files using BufferedReader Class

BufferedReader class is a subclass of the Reader class in Java. It is designed for efficient reading of characters from a character-based input stream.

One of the benefits of using BufferedReader is that it buffers the input, which makes reading faster and more efficient than reading characters one at a time.

Buffering for Efficient Reading

When we create a BufferedReader object, we can specify the size of the buffer. By default, the buffer size is set to 8192 bytes, which is a good size for most applications.

Here’s an example code snippet:

File file = new File(“filename.txt”);

FileReader fileReader = new FileReader(file);

BufferedReader bufferedReader = new BufferedReader(fileReader, 8192);

In this example, we create a BufferedReader object that reads from a file named “filename.txt”. We also set the buffer size to 8192 bytes by passing it as an argument to the constructor.

Reading Text from Character-based Input Stream

To read text data from a character-based input stream using BufferedReader, we use the readLine() function. The readLine() function reads a line of text from the input stream, which means it reads up to the newline character (‘n’) or the end of the stream.

Here’s an example code snippet:

BufferedReader bufferedReader = new BufferedReader(new FileReader(“filename.txt”));

String line = bufferedReader.readLine();

while (line != null) {

System.out.println(line);

line = bufferedReader.readLine();

}

In this example, we create a BufferedReader object that reads from a file named “filename.txt”. Then we use the readLine() function to read a line of text and assign it to the variable ‘line’.

We use a while loop to print out each line of text in the file until we reach the end of the stream.

Conclusion

In summary, reading text files in Java can be done using a variety of classes and methods, including InputStream, Scanner, and BufferedReader. The different classes have their strengths and weaknesses, making them useful for different situations.

By understanding these classes and their methods, Java developers can effectively read and store text data from various input sources in their applications.

5) Reading Text Files using FileReader Class

Java FileReader class is designed for extracting character data from text files. It is a subclass of the InputStreamReader class that can read any stream of data as a series of Unicode characters.

FileReader class is a convenient way to read plain text files because it reads characters directly from the file without the need for intermediate conversions.

Convenient Way to Read Plain Text

To create a FileReader object that reads from a file, we first need to create a File object that represents the file we want to read. Then we use that File object to create a FileReader object as shown in the following code:

File file = new File(“filename.txt”);

FileReader fileReader = new FileReader(file);

Here, we create a FileReader object named ‘fileReader’ that reads from the file “filename.txt”.

FileReader class provides several read() methods that can be used to read single characters or arrays of characters from the input stream.

Using Default Byte-buffer Size and Character Encoding

FileReader class reads data from a file in bytes, so an internal buffer is used to optimize reading performance. The default buffer size is 8192 bytes, which can be changed by passing it as an argument to the constructor.

FileReader class uses the default character encoding of the operating system to read character data from a text file. If the file is in a different encoding, a different constructor can be used to specify the encoding.

FileReader class is a simple and efficient way to read text files in Java.

6) File Reading Example

Let’s take a look at an example of reading a text file using Java FileReader class. In this example, we will create a new empty file and write some text to it.

Then we will read the same file using FileReader class and print out the contents of the file.

Creating New Empty File

To create a new empty file, we need to use the createNewFile() function available in the File class. Here’s how we can create an empty file named “newfile.txt”:

File file = new File(“newfile.txt”);

file.createNewFile();

In this example, we create a File object named ‘file’ that points to the file we want to create.

Then we use the createNewFile() function to create a new empty file called “newfile.txt”.

Checking File Existence

Before reading the contents of the file, we need to check if the file exists. Here’s how we can do it using the exists() function available in the File class:

if(file.exists()) {

System.out.println(“File exists”);

} else {

System.out.println(“File does not exist”);

}

In this example, we check if the file exists using the exists() function.

If the file exists, we print out “File exists”, otherwise, we print out “File does not exist”.

Reading Text from File

Now that the file exists, we can use FileReader class to read text data from the file. Here’s how we can do it:

FileReader fileReader = new FileReader(file);

int ch;

while ((ch = fileReader.read()) != -1) {

System.out.print((char)ch);

}

In this example, we create a FileReader object named ‘fileReader’ that reads from the file ‘file’.

Then we use fileReader.read() function to read characters one-by-one from the file until the end of file is reached (read() function returns -1 when there is no more data to read) and print each character.

Conclusion

In this article, we’ve looked at reading text files in Java using the FileReader class, including its default settings. We’ve also covered an example of creating an empty file and checking its existence before reading text data from the file using FileReader class.

Java FileReader class is a useful and efficient way to read text data from files, and understanding how to use it is a critical skill for any Java developer. In conclusion, reading text files is an essential task for any Java programmer.

This article covered several methods for reading text files in Java, including InputStream, Scanner, BufferedReader, and FileReader. Using these classes, developers can efficiently parse data from various input sources and store them in their applications.

It is significant to understand the differences between these methods and when to use each one effectively. Takeaways include creating an InputStream object, passing InputStream to the Scanner class, using default byte-buffer size and character encoding, creating new empty files, and checking file existence.

With these skills and knowledge, Java developers can effectively read and handle text files, improving the quality of their programming.

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