Java : FilterReader with Examples
Last Modified : June 3, 2023 Published : March 30, 2023
FilterReader (Java SE 19 & JDK 19) API Examples.
You will find code examples on most FilterReader methods.
Summary
Abstract class for reading filtered character streams. The abstract class FilterReader itself provides default methods that pass all requests to the contained stream.
class MyReader extends FilterReader {
MyReader(Reader in) {
super(in);
}
}
try (final var reader = new MyReader(new StringReader("abc"))) {
System.out.printf("%c%n", reader.read()); // a
System.out.printf("%c%n", reader.read()); // b
System.out.printf("%c%n", reader.read()); // c
System.out.println(reader.read()); // -1
}
Fields
protected Reader in
The underlying character-input stream.
class MyReader extends FilterReader {
MyReader(Reader in) {
super(in);
}
Reader getIn() {
return in;
}
}
final var sr = new StringReader("abc");
try (final var reader = new MyReader(sr)) {
System.out.println(reader.getIn() == sr); // true
}
Fields declared in Reader
Constructors
FilterReader (Reader in)
Creates a new filtered reader.
class MyReader extends FilterReader {
MyReader(Reader in) {
super(in);
}
}
try (final var reader = new MyReader(new StringReader("abc"))) {
System.out.printf("%c%n", reader.read()); // a
System.out.printf("%c%n", reader.read()); // b
System.out.printf("%c%n", reader.read()); // c
System.out.println(reader.read()); // -1
}
Methods
void close ()
Closes the stream and releases any system resources associated with it.
class MyReader extends FilterReader {
MyReader(Reader in) {
super(in);
}
}
try (final var reader = new MyReader(new StringReader("abc"))) {
System.out.printf("%c%n", reader.read()); // a
System.out.printf("%c%n", reader.read()); // b
System.out.printf("%c%n", reader.read()); // c
System.out.println(reader.read()); // -1
}
An example without try-with-resources.
class MyReader extends FilterReader {
MyReader(Reader in) {
super(in);
}
}
final var reader = new MyReader(new StringReader("abc"));
try {
System.out.printf("%c%n", reader.read()); // a
System.out.printf("%c%n", reader.read()); // b
System.out.printf("%c%n", reader.read()); // c
System.out.println(reader.read()); // -1
} finally {
reader.close();
}
void mark (int readAheadLimit)
Marks the present position in the stream.
class MyReader extends FilterReader {
MyReader(Reader in) {
super(in);
}
}
try (final var reader = new MyReader(new BufferedReader(new StringReader("abcde")))) {
System.out.printf("%c%n", reader.read()); // a
System.out.printf("%c%n", reader.read()); // b
System.out.printf("%c%n", reader.read()); // c
reader.mark(3);
System.out.printf("%c%n", reader.read()); // d
System.out.printf("%c%n", reader.read()); // e
System.out.println(reader.read()); // -1
reader.reset();
System.out.printf("%c%n", reader.read()); // d
System.out.printf("%c%n", reader.read()); // e
System.out.println(reader.read()); // -1
reader.reset();
reader.mark(2);
System.out.printf("%c%n", reader.read()); // d
System.out.printf("%c%n", reader.read()); // e
System.out.println(reader.read()); // -1
try {
reader.reset();
} catch (IOException e) {
System.out.println("IOException! : " + e.getMessage());
}
// Result
// ↓
//IOException! : Mark invalid
}
boolean markSupported ()
Tells whether this stream supports the mark() operation.
class MyReader extends FilterReader {
MyReader(Reader in) {
super(in);
}
}
{
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 = new MyReader(Files.newBufferedReader(path))) {
System.out.println(reader.markSupported()); // true
}
}
{
try (final var reader = new MyReader(new StringReader("abcd"))) {
System.out.println(reader.markSupported()); // true
}
}
{
final var url = new URL("https://example.com/");
try (final var reader = new MyReader(new InputStreamReader(url.openStream()))) {
System.out.println(reader.markSupported()); // false
}
}
int read ()
Reads a single character.
Please see FilterReader(Reader in).
int read (char[] cbuf, int off, int len)
Reads characters into a portion of an array.
class MyReader extends FilterReader {
MyReader(Reader in) {
super(in);
}
}
try (final var reader = new MyReader(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 MyReader(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 MyReader(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
}
boolean ready ()
Tells whether this stream is ready to be read.
class MyReader extends FilterReader {
MyReader(Reader in) {
super(in);
}
}
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 = new MyReader(Files.newBufferedReader(path))) {
System.out.println(reader.ready()); // true
System.out.printf("%c%n", reader.read()); // a
System.out.println(reader.ready()); // true
System.out.printf("%c%n", reader.read()); // b
System.out.println(reader.ready()); // true
System.out.printf("%c%n", reader.read()); // c
System.out.println(reader.ready()); // false
System.out.println(reader.read()); // -1
}
void reset ()
Resets the stream.
Please see mark(int readAheadLimit).
long skip (long n)
Skips characters.
class MyReader extends FilterReader {
MyReader(Reader in) {
super(in);
}
}
try (final var reader = new MyReader(new StringReader("abcdefghij"))) {
System.out.printf("%c%n", reader.read()); // a
System.out.println(reader.skip(1)); // 1
System.out.printf("%c%n", reader.read()); // c
System.out.println(reader.skip(2)); // 2
System.out.printf("%c%n", reader.read()); // f
System.out.println(reader.skip(3)); // 3
System.out.printf("%c%n", reader.read()); // j
System.out.println(reader.skip(1)); // 0
System.out.println(reader.read()); // -1
}
try (final var reader = new MyReader(new StringReader("abcde"))) {
System.out.printf("%c%n", reader.read()); // a
System.out.println(reader.skip(10)); // 4
System.out.println(reader.read()); // -1
}
Methods declared in Reader
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