Readers and Writers

Readers and Writers and their respective subclasses provide simple I/O for text / character-based data.

BufferedReader

Introduction

The BufferedReader class is a wrapper for other Reader classes that serves two main purposes:

  • A BufferedReader provides buffering for the wrapped Reader. This allows an application to read characters one at a time without undue I/O overheads.
  • A BufferedReader provides functionality for reading text a line at a time.

Basics of using a BufferedReader

The normal pattern for using a BufferedReader is as follows. First, you obtain the Reader that you want to read characters from. Next you instantiate a BufferedReader that wraps the Reader. Then you read character data. Finally you close the BufferedReader which close the wrapped `Reader. For example:

File someFile = new File(...);
int aCount = 0;
try (FileReader fr = new FileReader(someFile);
BufferedReader br = new BufferedReader(fr)) {
	// Count the number of 'a' characters.
	int ch;
	while ((ch = br.read()) != -1) {
		if (ch == 'a') {
			aCount++;
		}
	}
	System.out.println("There are " + aCount + " 'a' characters in " + someFile);
}

You can apply this pattern to any Reader

Notes:

  • We have used Java 7 (or later) try-with-resources to ensure that the underlying reader is always closed. This avoids a potential resource leak. In earlier versions of Java, you would explicitly close the BufferedReader in a finally block.
  • The code inside the try block is virtually identical to what we would use if we read directly from the FileReader. In fact, a BufferedReader functions exactly like the Reader that it wraps would behave. The difference is that this version is a lot more efficient.

The BufferedReader buffer size
The BufferedReader.readLine() method
Example: reading all lines of a File into a List

This is done by getting each line in a file, and adding it into a List<String>. The list is then returned:

public List<String> getAllLines(String filename) throws IOException {
	List<String> lines = new ArrayList<String>();
	try (BufferedReader br = new BufferedReader(new FileReader(filename))) {
		String line = null;
		while ((line = reader.readLine) != null) {
			lines.add(line);
		}
	}
	return lines;
}

Java 8 provides a more concise way to do this using the lines() method:

public List<String> getAllLines(String filename) throws IOException {
	try (BufferedReader br = new BufferedReader(new FileReader(filename))) {
		return br.lines().collect(Collectors.toList());
	}
	return Collections.empty();
}

StringWriter Example

Java StringWriter class is a character stream that collects output from string buffer, which can be used to construct a string.

The StringWriter class extends the Writer class.

In StringWriter class, system resources like network sockets and files are not used, therefore closing the StringWriter is not necessary.

import java.io.*; 
public class StringWriterDemo { 
	public static void main(String[] args) throws IOException { 
		char[] ary = new char[1024]; 
		StringWriter writer = new StringWriter(); 
		FileInputStream input = null; 
		BufferedReader buffer = null; 
		input = new FileInputStream("c://stringwriter.txt"); 
		buffer = new BufferedReader(new InputStreamReader(input, "UTF-8")); 
		int x; 
		while ((x = buffer.read(ary)) != -1) { 
			writer.write(ary, 0, x); 
		}
		System.out.println(writer.toString()); 
		writer.close(); 
		buffer.close(); 
	}
}

The above example helps us to know simple example of StringWriter using BufferedReader to read file data from the stream.

Basic Programs

Learn All in Tamil © Designed & Developed By Tutor Joes | Privacy Policy | Terms & Conditions