Java : BufferedReader with Examples
Last Modified : January 13, 2024 Published : April 24, 2022
BufferedReader (Java SE 17 & JDK 17) API Examples.
You will find code examples on most BufferedReader methods.
Summary
Reads text from a character-input stream, buffering characters so as to provide for the efficient reading of characters, arrays, and lines.
final var path = Path.of("R:", "java-work", "aaa.txt");
System.out.println(path); // R:\java-work\aaa.txt
Files.writeString(path, """
abcd
XYZ
12345
""");
// --- PowerShell ---
//PS R:\java-work> ls | Format-Table -Property Mode, Length, Name
//
//Mode Length Name
//---- ------ ----
//-a--- 15 aaa.txt
try (final var reader = Files.newBufferedReader(path)) {
System.out.println(reader.readLine()); // abcd
System.out.println(reader.readLine()); // XYZ
System.out.println(reader.readLine()); // 12345
System.out.println(reader.readLine()); // null
}
Fields declared in Reader
Constructors
BufferedReader (Reader in)
Creates a buffering character-input stream that uses a default-sized input buffer.
final var s = """
abcd
XYZ
""";
try (final var reader = new BufferedReader(new StringReader(s))) {
System.out.println(reader.readLine()); // abcd
System.out.println(reader.readLine()); // XYZ
System.out.println(reader.readLine()); // null
}
BufferedReader (Reader in, int sz)
Creates a buffering character-input stream that uses an input buffer of the specified size.
final var s = """
abcd
XYZ
""";
try (final var reader = new BufferedReader(new StringReader(s), 128)) {
System.out.println(reader.readLine()); // abcd
System.out.println(reader.readLine()); // XYZ
System.out.println(reader.readLine()); // null
}
Methods
void close ()
Closes the stream and releases any system resources associated with it.
final var path = Path.of("R:", "java-work", "aaa.txt");
System.out.println(path); // R:\java-work\aaa.txt
Files.writeString(path, "abcd");
try (final var reader = Files.newBufferedReader(path)) {
final var cbuf = new char[4];
System.out.println(reader.read(cbuf)); // 4
System.out.println(Arrays.toString(cbuf)); // [a, b, c, d]
}
// An example without a try-with-resources statement.
final var path = Path.of("R:", "java-work", "aaa.txt");
System.out.println(path); // R:\java-work\aaa.txt
Files.writeString(path, "abcd");
final var reader = Files.newBufferedReader(path);
try {
final var cbuf = new char[4];
System.out.println(reader.read(cbuf)); // 4
System.out.println(Arrays.toString(cbuf)); // [a, b, c, d]
} finally {
reader.close();
}
Stream<String> lines ()
Returns a Stream, the elements of which are lines read from this BufferedReader.
final var path = Path.of("R:", "java-work", "aaa.txt");
System.out.println(path); // R:\java-work\aaa.txt
Files.writeString(path, """
abcd
XYZ
12345
""");
// --- PowerShell ---
//PS R:\java-work> ls | Format-Table -Property Mode, Length, Name
//
//Mode Length Name
//---- ------ ----
//-a--- 15 aaa.txt
try (final var reader = Files.newBufferedReader(path)) {
final var lines = reader.lines();
lines.forEach(System.out::println);
}
// Result
// ↓
//abcd
//XYZ
//12345
void mark (int readAheadLimit)
Marks the present position in the stream.
try (final var reader = new BufferedReader(new StringReader("abcde"))) {
System.out.println("%c".formatted(reader.read())); // a
System.out.println("%c".formatted(reader.read())); // b
System.out.println("%c".formatted(reader.read())); // c
reader.mark(3);
System.out.println("%c".formatted(reader.read())); // d
System.out.println("%c".formatted(reader.read())); // e
System.out.println(reader.read()); // -1
reader.reset();
System.out.println("%c".formatted(reader.read())); // d
System.out.println("%c".formatted(reader.read())); // e
System.out.println(reader.read()); // -1
reader.reset();
reader.mark(2);
System.out.println("%c".formatted(reader.read())); // d
System.out.println("%c".formatted(reader.read())); // e
System.out.println(reader.read()); // -1
try {
reader.reset();
} catch (IOException e) {
System.out.println(e);
}
// Result
// ↓
//java.io.IOException: Mark invalid
}
boolean markSupported ()
Tells whether this stream supports the mark() operation, which it does.
try (final var reader = Files.newBufferedReader(Path.of("R:", "java-work", "aaa.txt"))) {
System.out.println(reader.markSupported()); // true
}
try (final var reader = new BufferedReader(new StringReader("abcd"))) {
System.out.println(reader.markSupported()); // true
}
int read ()
Reads a single character.
try (final var reader = new BufferedReader(new StringReader("abc"))) {
System.out.println("%c".formatted(reader.read())); // a
System.out.println("%c".formatted(reader.read())); // b
System.out.println("%c".formatted(reader.read())); // c
System.out.println(reader.read()); // -1
}
int read (char[] cbuf, int off, int len)
Reads characters into a portion of an array.
try (final var reader = new BufferedReader(new StringReader("abcdefg"))) {
final var cbuf = new char[5];
System.out.println(reader.read(cbuf, 0, 1)); // 1
System.out.println(Arrays.toString(cbuf)); // [a, , , , ]
System.out.println(reader.read(cbuf, 0, 2)); // 2
System.out.println(Arrays.toString(cbuf)); // [b, c, , , ]
System.out.println(reader.read(cbuf, 0, 3)); // 3
System.out.println(Arrays.toString(cbuf)); // [d, e, f, , ]
System.out.println(reader.read(cbuf, 0, 4)); // 1
System.out.println(Arrays.toString(cbuf)); // [g, e, f, , ]
System.out.println(reader.read(cbuf, 0, 5)); // -1
System.out.println(Arrays.toString(cbuf)); // [g, e, f, , ]
}
try (final var reader = new BufferedReader(new StringReader("abcde"))) {
final var cbuf = new char[5];
System.out.println(reader.read(cbuf, 4, 1)); // 1
System.out.println(Arrays.toString(cbuf)); // [ , , , , a]
System.out.println(reader.read(cbuf, 3, 1)); // 1
System.out.println(Arrays.toString(cbuf)); // [ , , , b, a]
System.out.println(reader.read(cbuf, 2, 1)); // 1
System.out.println(Arrays.toString(cbuf)); // [ , , c, b, a]
System.out.println(reader.read(cbuf, 1, 1)); // 1
System.out.println(Arrays.toString(cbuf)); // [ , d, c, b, a]
System.out.println(reader.read(cbuf, 0, 1)); // 1
System.out.println(Arrays.toString(cbuf)); // [e, d, c, b, a]
}
try (final var reader = new BufferedReader(new StringReader("abcdefg"))) {
final var cbuf = new char[3];
System.out.println(reader.read(cbuf, 0, 3)); // 3
System.out.println(Arrays.toString(cbuf)); // [a, b, c]
//reader.read(cbuf, 0, 4); // IndexOutOfBoundsException
//reader.read(cbuf, 3, 1); // IndexOutOfBoundsException
}
String readLine ()
Reads a line of text.
final var path = Path.of("R:", "java-work", "aaa.txt");
System.out.println(path); // R:\java-work\aaa.txt
Files.writeString(path, """
abcd
XYZ
12345
""");
// --- PowerShell ---
//PS R:\java-work> ls | Format-Table -Property Mode, Length, Name
//
//Mode Length Name
//---- ------ ----
//-a--- 15 aaa.txt
try (final var reader = Files.newBufferedReader(path)) {
System.out.println(reader.readLine()); // abcd
System.out.println(reader.readLine()); // XYZ
System.out.println(reader.readLine()); // 12345
System.out.println(reader.readLine()); // null
}
boolean ready ()
Tells whether this stream is ready to be read.
final var path = Path.of("R:", "java-work", "aaa.txt");
System.out.println(path); // R:\java-work\aaa.txt
Files.writeString(path, "abc");
try (final var reader = Files.newBufferedReader(path)) {
System.out.println(reader.ready()); // true
System.out.println("%c".formatted(reader.read())); // a
System.out.println(reader.ready()); // true
System.out.println("%c".formatted(reader.read())); // b
System.out.println(reader.ready()); // true
System.out.println("%c".formatted(reader.read())); // c
System.out.println(reader.ready()); // false
System.out.println(reader.read()); // -1
}
void reset ()
Resets the stream to the most recent mark.
Please see mark(int readAheadLimit).
Methods declared in Reader
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