Класс Java.io.Reader в Java

Опубликовано: 15 Февраля, 2022

Это абстрактный класс для чтения символьных потоков. Единственные методы, которые должен реализовывать подкласс, - это read (char [], int, int) и close (). Однако большинство подклассов переопределят некоторые из методов, определенных здесь, чтобы обеспечить более высокую эффективность, дополнительную функциональность или и то, и другое.
Конструкторы:

protected Reader (): создает новый считыватель потока символов, критические разделы которого будут синхронизироваться с самим считывателем.
protected Reader (Блокировка объекта): Создает новый считыватель потока символов, критические разделы которого будут синхронизироваться с данным объектом.

Methods:

abstract void close() : Closes the stream and releases any system resources associated with it. Once the stream has been closed, further read(), ready(), mark(), reset(), or skip() invocations will throw an IOException. Closing a previously closed stream has no effect.
```
Syntax :public abstract void close()
                    throws IOException
Throws:
IOException 
```

void mark(int readAheadLimit) : Marks the present position in the stream.Subsequent calls to reset() will attempt to reposition the stream to this point. Not all character-input streams support the mark() operation.

Syntax :public void mark(int readAheadLimit)
          throws IOException
Parameters:
readAheadLimit - Limit on the number of characters that may be read
while still preserving the mark. After reading this many characters, 
attempting to reset the stream may fail.
Throws:
IOException

boolean markSupported() : Tells whether this stream supports the mark() operation.The default implementation always returns false. Subclasses should override this method.
```
Syntax :public boolean markSupported()
Returns:
true if and only if this stream supports the mark operation.
```
int read() : Reads a single character. This method will block until a character is available, an I/O error occurs, or the end of the stream is reached.
Subclasses that intend to support efficient single-character input should override this method.
```
Syntax :public int read()
         throws IOException
Returns:
The character read, as an integer in the range 0 to 65535 (0x00-0xffff), 
or -1 if the end of the stream has been reached
Throws:
IOException 
```

int read(char[] cbuf) : Reads characters into an array.This method will block until some input is available, an I/O error occurs, or the end of the stream is reached.

Syntax :public int read(char[] cbuf)
         throws IOException
Parameters:
cbuf - Destination buffer
Returns:
The number of characters read, or -1 if the end of the stream has been reached
Throws:
IOException

abstract int read(char[] cbuf, int off, int len) : Reads characters into a portion of an array.This method will block until some input is available, an I/O error occurs, or the end of the stream is reached.

Syntax :public abstract int read(char[] cbuf,
       int off,
       int len)
                  throws IOException
Parameters:
cbuf - Destination buffer
off - Offset at which to start storing characters
len - Maximum number of characters to read
Returns:
The number of characters read, or -1 if the end of the stream has been reached
Throws:
IOException

int read(CharBuffer target) : Attempts to read characters into the specified character buffer.The buffer is used as a repository of characters as-is: the only changes made are the results of a put operation. No flipping or rewinding of the buffer is performed.

Syntax :public int read(CharBuffer target)
         throws IOException
Parameters:
target - the buffer to read characters into
Returns:
The number of characters added to the buffer, 
or -1 if this source of characters is at its end
Throws:
IOException 
NullPointerException
ReadOnlyBufferException

boolean ready() : Tells whether this stream is ready to be read.

Syntax :public boolean ready()
              throws IOException
Returns:
True if the next read() is guaranteed not to block for input, false otherwise. 
Note that returning false does not guarantee that the next read will block.
Throws:
IOException

void reset() : Resets the stream. If the stream has been marked, then attempt to reposition it at the mark. If the stream has not been marked, then attempt to reset it in some way appropriate to the particular stream, for example by repositioning it to its starting point. Not all character-input streams support the reset() operation, and some support reset() without supporting mark().
```
Syntax :public void reset()
           throws IOException
Throws:
IOException
```

long skip(long n) : Skips characters.This method will block until some characters are available, an I/O error occurs, or the end of the stream is reached.

Syntax :public long skip(long n)
          throws IOException
Parameters:
n - The number of characters to skip
Returns:
The number of characters actually skipped
Throws:
IllegalArgumentException - If n is negative.
IOException

//Java program demonstrating Reader methods
import java.io.*;
import java.nio.CharBuffer;
import java.util.Arrays;
class ReaderDemo
{
    public static void main(String[] args) throws IOException
    {
        Reader r = new FileReader("file.txt");
        PrintStream out = System.out;
        char c[] = new char[10];
        CharBuffer cf = CharBuffer.wrap(c);
  
        //illustrating markSupported()
        if(r.markSupported()) {
            //illustrating mark()
            r.mark(100);
            out.println("mark method is supported");
        }
        //skipping 5 characters
        r.skip(5);
  
        //checking whether this stream is ready to be read.
        if(r.ready()) 
        {
            //illustrating read(char[] cbuf,int off,int len)
            r.read(c,0,10);
            out.println(Arrays.toString(c));
  
            //illustrating read(CharBuffer target )
            r.read(cf);
            out.println(Arrays.toString(cf.array()));
              
            //illustrating read()
            out.println((char)r.read());
        }
        //closing the stream
        r.close();
    }
}

Выход :

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Автор статьи - Нишант Шарма . Если вам нравится GeeksforGeeks, и вы хотели бы внести свой вклад, вы также можете написать статью с помощью provide.geeksforgeeks.org или отправить ее по электронной почте на deposit@geeksforgeeks.org. Посмотрите, как ваша статья появляется на главной странице GeeksforGeeks, и помогите другим гикам.

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Класс Java.io.Reader в Java

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