Java Language Readers and Writers BufferedReader
Example
Introduction
The BufferedReader class is a wrapper for other Reader classes that serves two main purposes:
-
A
BufferedReaderprovides buffering for the wrappedReader. This allows an application to read characters one at a time without undue I/O overheads. -
A
BufferedReaderprovides 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
BufferedReaderin afinallyblock. -
The code inside the
tryblock is virtually identical to what we would use if we read directly from theFileReader. In fact, aBufferedReaderfunctions exactly like theReaderthat 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();
}
