Package java.io

Class Reader

java.lang.Object
java.io.Reader
All Implemented Interfaces:
Closeable, AutoCloseable, Readable
Direct Known Subclasses:
BufferedReader, CharArrayReader, FilterReader, InputStreamReader, PipedReader, StringReader
public abstract class Reader
extends Object
implements Readable, Closeable
The base class for all readers. A reader is a means of reading data from a source in a character-wise manner. Some readers also support marking a position in the input and returning to this position later.

This abstract class does not provide a fully working implementation, so it needs to be subclassed, and at least the read(char[], int, int) and close() methods needs to be overridden. Overriding some of the non-abstract methods is also often advised, since it might result in higher efficiency.

Many specialized readers for purposes like reading from a file already exist in this package.

See Also:
Writer

  • Field Summary

    Fields
    Modifier and Type Field Description
    protected Object lock
    The object used to synchronize access to the reader.

  • Constructor Summary

    Constructors
    Modifier Constructor Description
    protected Reader()
    Constructs a new Reader with this as the object used to synchronize critical sections.
    protected Reader​(Object lock)
    Constructs a new Reader with lock used to synchronize critical sections.

  • Method Summary

    Modifier and Type Method Description
    abstract void close()
    Closes this reader.
    void mark​(int readLimit)
    Sets a mark position in this reader.
    boolean markSupported()
    Indicates whether this reader supports the mark() and reset() methods.
    int read()
    Reads a single character from this reader and returns it as an integer with the two higher-order bytes set to 0.
    int read​(char[] buffer)
    Reads characters from this reader and stores them in the character array buffer starting at offset 0.
    abstract int read​(char[] buffer, int offset, int count)
    Reads up to count characters from this reader and stores them at offset in the character array buffer.
    int read​(CharBuffer target)
    Reads characters and puts them into the target character buffer.
    boolean ready()
    Indicates whether this reader is ready to be read without blocking.
    void reset()
    Resets this reader's position to the last mark() location.
    long skip​(long charCount)
    Skips charCount characters in this reader.

    Methods inherited from class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

  • Field Details

    • lock

      protected Object lock
      The object used to synchronize access to the reader.

  • Constructor Details

    • Reader

      protected Reader()
      Constructs a new Reader with this as the object used to synchronize critical sections.

    • Reader

      protected Reader​(Object lock)
      Constructs a new Reader with lock used to synchronize critical sections.
      Parameters:
      lock - the Object used to synchronize critical sections.
      Throws:
      NullPointerException - if lock is null.

  • Method Details

    • close

      public abstract void close() throws IOException
      Closes this reader. Implementations of this method should free any resources associated with the reader.
      Specified by:
      close in interface AutoCloseable
      Specified by:
      close in interface Closeable
      Throws:
      IOException - if an error occurs while closing this reader.

    • mark

      public void mark​(int readLimit) throws IOException
      Sets a mark position in this reader. The parameter readLimit indicates how many characters can be read before the mark is invalidated. Calling reset() will reposition the reader back to the marked position if readLimit has not been surpassed.

      This default implementation simply throws an IOException; subclasses must provide their own implementation.

      Parameters:
      readLimit - the number of characters that can be read before the mark is invalidated.
      Throws:
      IllegalArgumentException - if readLimit < 0.
      IOException - if an error occurs while setting a mark in this reader.
      See Also:
      markSupported(), reset()

    • markSupported

      public boolean markSupported()
      Indicates whether this reader supports the mark() and reset() methods. This default implementation returns false.
      Returns:
      always false.

    • read

      public int read() throws IOException
      Reads a single character from this reader and returns it as an integer with the two higher-order bytes set to 0. Returns -1 if the end of the reader has been reached.
      Returns:
      the character read or -1 if the end of the reader has been reached.
      Throws:
      IOException - if this reader is closed or some other I/O error occurs.

    • read

      public int read​(char[] buffer) throws IOException
      Reads characters from this reader and stores them in the character array buffer starting at offset 0. Returns the number of characters actually read or -1 if the end of the reader has been reached.
      Throws:
      IOException - if this reader is closed or some other I/O error occurs.

    • read

      public abstract int read​(char[] buffer, int offset, int count) throws IOException
      Reads up to count characters from this reader and stores them at offset in the character array buffer. Returns the number of characters actually read or -1 if the end of the reader has been reached.
      Throws:
      IOException - if this reader is closed or some other I/O error occurs.

    • ready

      public boolean ready() throws IOException
      Indicates whether this reader is ready to be read without blocking. Returns true if this reader will not block when read is called, false if unknown or blocking will occur. This default implementation always returns false.
      Returns:
      always false.
      Throws:
      IOException - if this reader is closed or some other I/O error occurs.
      See Also:
      read(), read(char[]), read(char[], int, int)

    • reset

      public void reset() throws IOException
      Resets this reader's position to the last mark() location. Invocations of read() and skip() will occur from this new location. If this reader has not been marked, the behavior of reset() is implementation specific. This default implementation throws an IOException.
      Throws:
      IOException - always thrown in this default implementation.
      See Also:
      mark(int), markSupported()

    • skip

      public long skip​(long charCount) throws IOException
      Skips charCount characters in this reader. Subsequent calls of read methods will not return these characters unless reset is used. This method may perform multiple reads to read charCount characters.
      Returns:
      the number of characters actually skipped.
      Throws:
      IllegalArgumentException - if charCount < 0.
      IOException - if this reader is closed or some other I/O error occurs.
      See Also:
      mark(int), markSupported(), reset()

    • read

      public int read​(CharBuffer target) throws IOException
      Reads characters and puts them into the target character buffer.
      Specified by:
      read in interface Readable
      Parameters:
      target - the destination character buffer.
      Returns:
      the number of characters put into target or -1 if the end of this reader has been reached before a character has been read.
      Throws:
      IOException - if any I/O error occurs while reading from this reader.
      NullPointerException - if target is null.
      ReadOnlyBufferException - if target is read-only.