Java : StringReader with Examples

try (final var reader = new StringReader("abc")) {
    final var ret1 = reader.read();
    System.out.printf("%d : %c%n", ret1, ret1); // 97 : a

    final var ret2 = reader.read();
    System.out.printf("%d : %c%n", ret2, ret2); // 98 : b

    final var ret3 = reader.read();
    System.out.printf("%d : %c%n", ret3, ret3); // 99 : c

    final var ret4 = reader.read();
    System.out.println(ret4); // -1
}

final var s = """
        abcd
        XYZ
        12345
        """;
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()); // 12345
    System.out.println(reader.readLine()); // null
}

lock

Please see the link below.

• Java API Examples : Reader

StringReader (String s)

Creates a new string reader.

try (final var reader = new StringReader("abcd")) {
    final var cbuf = new char[4];

    System.out.println(reader.read(cbuf)); // 4
    System.out.println(Arrays.toString(cbuf)); // [a, b, c, d]
}

void close ()

Closes the stream and releases any system resources associated with it.

try (final var reader = new StringReader("abcd")) {
    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 reader = new StringReader("abcd");
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();
}

// Once the reader has been closed, read methods will throw an IOException. 
try {
    reader.read();
} catch (IOException e) {
    System.out.println(e);

    // Result
    // ↓
    //java.io.IOException: Stream closed
}

void mark (int readAheadLimit)

Marks the present position in the stream.

try (final var reader = 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

    // A readAheadLimit is ignored.
    reader.mark(0);

    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
}

boolean markSupported ()

Tells whether this stream supports the mark() operation, which it does.

try (final var reader = new StringReader("abcd")) {
    System.out.println(reader.markSupported()); // true
}

int read ()

Reads a single character.

try (final var reader = new StringReader("abc")) {
    final var ret1 = reader.read();
    System.out.printf("%d : %c%n", ret1, ret1); // 97 : a

    final var ret2 = reader.read();
    System.out.printf("%d : %c%n", ret2, ret2); // 98 : b

    final var ret3 = reader.read();
    System.out.printf("%d : %c%n", ret3, ret3); // 99 : c

    final var ret4 = reader.read();
    System.out.println(ret4); // -1
}

int read (char[] cbuf, int off, int len)

Reads characters into a portion of an array.

try (final var reader = 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 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 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.

try (final var reader = new StringReader("abc")) {
    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()); // true
    System.out.println(reader.read()); // -1
}

void reset ()

Resets the stream to the most recent mark, or to the beginning of the string if it has never been marked.

Please see mark(int readAheadLimit).

long skip (long n)

Skips characters.

try (final var reader = 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 Reader reader = new StringReader("abcde")) {
    System.out.printf("%c%n", reader.read()); // a

    System.out.println(reader.skip(10)); // 4
    System.out.println(reader.read()); // -1
}

nullReader, read, read, transferTo

Please see the link below.

• Java API Examples : Reader