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Category: 09. Java.io package

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  • ObjectStreamClass 

    Introduction

    The Java.io.ObjectStreamClass class is Serialization’s descriptor for classes. It contains the name and serialVersionUID of the class. The ObjectStreamClass for a specific class loaded in this Java VM can be found/created using the lookup method.

    Class declaration

    Following is the declaration for Java.io.ObjectStreamClass class −

    public class ObjectStreamClass
   extends Object

      implements Serializable

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    Field

    Following are the fields for Java.io.ObjectStreamClass class −

    • static ObjectStreamField[] NO_FIELDS − This is the serialPersistentFields value indicating no serializable fields.

    Class methods

    Sr.No.Method & Description
    1Class<?> forClass()This method returns the class in the local VM that this version is mapped to.
    2ObjectStreamField getField(String name)This method gets the field of this class by name.
    3ObjectStreamField[] getFields()This method returns an array of the fields of this serializable class.
    4String getName()This method returns the name of the class described by this descriptor.
    5long getSerialVersionUID()This method returns the serialVersionUID for this class.
    6static ObjectStreamClass lookup(Class<?> cl)This method finds the descriptor for a class that can be serialized.
    7static ObjectStreamClass lookupAny(Class<?> cl)This method returns the descriptor for any class, regardless of whether it implements Serializable.
    8String toString()This method returns a string describing this ObjectStreamClass.

    Methods inherited

    This class inherits methods from the following classes −

    • Java.io.Object

  • ObjectOutputStream.PutField

    Introduction

    The Java.io.ObjectOutputStream.PutField class provide programmatic access to the persistent fields to be written to ObjectOutput.

    Class declaration

    Following is the declaration for Java.io.ObjectOutputStream.PutField class −

    public abstract static class ObjectOutputStream.PutField
   extends Object

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    Class constructors

    Sr.No.Constructor & Description
    1ObjectOutputStream.PutField()Single Constructor

    Class methods

    Sr.No.Method & Description
    1abstract void put(String name, boolean val)This method puts the value of the named boolean field into the persistent field.
    2abstract void put(String name, byte val)This method puts the value of the named byte field into the persistent field.
    3abstract void put(String name, char val)This method puts the value of the named char field into the persistent field.
    4abstract void put(String name, double val)This method puts the value of the named double field into the persistent field.
    5abstract void put(String name, float val)This method puts the value of the named float field into the persistent field.
    6abstract void put(String name, int val)This method puts the value of the named int field into the persistent field.
    7abstract void put(String name, long val)This method puts the value of the named long field into the persistent field.
    8abstract void put(String name, Object val)This method puts the value of the named Object field into the persistent field.
    9abstract void put(String name, short val)This method puts the value of the named short field into the persistent field.

    Methods inherited

    This class inherits methods from the following classes −

    • Java.io.Object

  • ObjectOutputStream 

    Introduction

    The Java.io.ObjectOutputStream class writes primitive data types and graphs of Java objects to an OutputStream.The objects can be read (reconstituted) using an ObjectInputStream.

    Class declaration

    Following is the declaration for Java.io.ObjectOutputStream class −

    public class ObjectOutputStream
   extends OutputStream

      implements ObjectOutput, ObjectStreamConstants

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    Class constructors

    Sr.No.Constructor & Description
    1protected ObjectOutputStream()This provides a way for subclasses that are completely reimplementing ObjectOutputStream to not have to allocate private data just used by this implementation of ObjectOutputStream.
    2ObjectOutputStream(OutputStream out)This creates an ObjectOutputStream that writes to the specified OutputStream.

    Class methods

    Sr.No.Method & Description
    1protected void annotateClass(Class <?> cl)Subclasses may implement this method to allow class data to be stored in the stream.
    2protected void annotateProxyClass(Class<?> cl)Subclasses may implement this method to store custom data in the stream along with descriptors for dynamic proxy classes.
    3void close()This method closes the stream.
    4void defaultWriteObject()This method writes the non-static and non-transient fields of the current class to this stream.
    5protected void drain()This method drain any buffered data in ObjectOutputStream.
    6protected boolean enableReplaceObject(boolean enable)This method enable the stream to do replacement of objects in the stream.
    7void flush()This method flushes the stream.
    8ObjectOutputStream.PutField putFields()This method retrieves the object used to buffer persistent fields to be written to the stream.
    9protected Object replaceObject(Object obj)This method will allow trusted subclasses of ObjectOutputStream to substitute one object for another during serialization.
    10void reset()This method reset will disregard the state of any objects already written to the stream.
    11void useProtocolVersion(int version)This method specify stream protocol version to use when writing the stream.
    12void write(byte[] buf)This method writes an array of bytes.
    13void write(byte[] buf, int off, int len)This method writes a sub array of bytes.
    14void write(int val)This method writes a byte.
    15void writeBoolean(boolean val)This method writes a boolean.
    16void writeByte(int val)This method writes an 8 bit byte.
    17void writeBytes(String str)This method writes a String as a sequence of bytes.
    18void writeChar(int val)This method writes a 16 bit char.
    19void writeChars(String str)This method writes a String as a sequence of chars.
    20protected void writeClassDescriptor(ObjectStreamClass desc)This method writes the specified class descriptor to the ObjectOutputStream.
    21void writeDouble(double val)This method writes a 64 bit double.
    22void writeFields()This method writes the buffered fields to the stream.
    23void writeFloat(float val)This method writes a 32 bit float.
    24void writeInt(int val)This method writes a 32 bit int.
    25void writeLong(long val)This method writes a 64 bit long.
    26void writeObject(Object obj)This method writes the specified object to the ObjectOutputStream.
    27protected void writeObjectOverride(Object obj)This method is used by subclasses to override the default writeObject method.
    28void writeShort(int val)This method writes a 16 bit short.
    29protected void writeStreamHeader()This method is provided so subclasses can append or prepend their own header to the stream.
    30void writeUnshared(Object obj)This method writes an “unshared” object to the ObjectOutputStream.

    Methods inherited

    This class inherits methods from the following classes −

    • Java.io.Object

  • ObjectInputStream.GetField

    Introduction

    The Java.io.ObjectInputStream.GetField class provide access to the persistent fields read from the input stream.

    Class declaration

    Following is the declaration for Java.io.ObjectInputStream.GetField class −

    public abstract static class ObjectInputStream.GetField
   extends Object

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    Class constructors

    Sr.No.Constructor & Description
    1ObjectInputStream.GetField()Single Constructor

    Class methods

    Sr.No.Method & Description
    1abstract boolean defaulted(String name)This method return true if the named field is defaulted and has no value in this stream.
    2abstract boolean get(String name, boolean val)This method gets the value of the named boolean field from the persistent field.
    3abstract byte get(String name, byte val)This method gets the value of the named byte field from the persistent field.
    4abstract char get(String name, char val)This method gets the value of the named char field from the persistent field.
    5abstract double get(String name, double val)This method gets the value of the named double field from the persistent field.
    6abstract float get(String name, float val)This method gets the value of the named float field from the persistent field.
    7abstract int get(String name, int val)This method gets the value of the named int field from the persistent field.
    8abstract long get(String name, long val)This method gets the value of the named long field from the persistent field.
    9abstract Object get(String name, Object val)This method get the value of the named Object field from the persistent field.
    10abstract short get(String name, short val)This method gets the value of the named short field from the persistent field.
    11abstract ObjectStreamClass getObjectStreamClass()This method gets the ObjectStreamClass that describes the fields in the stream.

    Methods inherited

    This class inherits methods from the following classes −

    • Java.io.Object

  • ObjectInputStream 

    Introduction

    The Java.io.ObjectInputStream class deserializes primitive data and objects previously written using an ObjectOutputStream. Following are the important points about BufferedInputStream −

    • It is used to recover those objects previously serialized. It ensures that the types of all objects in the graph created from the stream match the classes present in the Java Virtual Machine.
    • Classes are loaded as required using the standard mechanisms.

    Class declaration

    Following is the declaration for Java.io.ObjectInputStream class −

    public class ObjectInputStream
   extends InputStream

      implements ObjectInput, ObjectStreamConstants

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    Class constructors

    Sr.No.Constructor & Description
    1protected ObjectInputStream()This provide a way for subclasses that are completely reimplementing ObjectInputStream to not have to allocate private data just used by this implementation of ObjectInputStream.
    2ObjectInputStream(InputStream in)This creates an ObjectInputStream that reads from the specified InputStream.

    Class methods

    Sr.No.Method & Description
    1int available()This method returns the number of bytes that can be read without blocking.
    2void close()This method closes the input stream.
    3void defaultReadObject()This method reads the non-static and non-transient fields of the current class from this stream.
    4protected boolean enableResolveObject(boolean enable)This method enables the stream to allow objects read from the stream to be replaced.
    5int read()This method reads a byte of data.
    6int read(byte[] buf, int off, int len)This method reads into an array of bytes.
    7boolean readBoolean()This method reads in a boolean.
    8byte readByte()This method reads an 8 bit byte.
    9char readChar()This method r a 16 bit char.
    10protected ObjectStreamClass readClassDescriptor()This method read a class descriptor from the serialization stream.
    11double readDouble()This method reads a 64 bit double.
    12ObjectInputStream.GetField readFields()This method reads the persistent fields from the stream and makes them available by name.
    13float readFloat()This method reads a 32 bit float.
    14void readFully(byte[] buf)This method reads bytes, blocking until all bytes are read.
    15void readFully(byte[] buf, int off, int len)This method reads bytes, blocking until all bytes are read.
    16int readInt()This method reads a 32 bit int.
    17long readLong()This method reads a 64 bit long.
    18Object readObject()This method reads an object from the ObjectInputStream.
    19protected Object readObjectOverride()This method is called by trusted subclasses of ObjectOutputStream that constructed ObjectOutputStream using the protected no-arg constructor.
    20short readShort()This method reads a 16 bit short.
    21protected void readStreamHeader()This method is provided to allow subclasses to read and verify their own stream headers.
    22Object readUnshared()This method reads an “unshared” object from the ObjectInputStream.
    23int readUnsignedByte()This method reads an unsigned 8 bit byte.
    24int readUnsignedShort()This method reads an unsigned 16 bit short.
    25String readUTF()This method reads a String in modified UTF-8 format.
    26void registerValidation(ObjectInputValidation obj, int prio)This method register an object to be validated before the graph is returned.
    27protected Class<?> resolveClass(ObjectStreamClass desc)This method loads the local class equivalent of the specified stream class description.
    28protected Object resolveObject(Object obj)This method will allow trusted subclasses of ObjectInputStream to substitute one object for another during deserialization.
    29protected Class<?> resolveProxyClass(String[] interfaces)This method returns a proxy class that implements the interfaces named in a proxy class descriptor; subclasses may implement this method to read custom data from the stream along with the descriptors for dynamic proxy classes, allowing them to use an alternate loading mechanism for the interfaces and the proxy class.
    30int skipBytes(int len)This method skips bytes.

    Methods inherited

    This class inherits methods from the following classes −

    • Java.io.InputStream
    • Java.io.Object
    • Java.io.ObjectInput

  • LineNumberReader 

    Introduction

    The Java.io.LineNumberReader class is a buffered character-input stream that keeps track of line numbers.A line is considered to be terminated by any one of a line feed (‘\n’), a carriage return (‘\r’), or a carriage return followed immediately by a linefeed.

    Class declaration

    Following is the declaration for Java.io.LineNumberReader class −

    public class LineNumberReader
   extends BufferedReader

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    Field

    Following are the fields for Java.io.LineNumberReader class −

    • protected Object lock − This is the object used to synchronize operations on this stream.

    Class constructors

    Sr.No.Constructor & Description
    1LineNumberReader(Reader in)This creates a new line-numbering reader, using the default input-buffer size.
    2LineNumberReader(Reader in, int sz)This creates a new line-numbering reader, reading characters into a buffer of the given size.

    Class methods

    Sr.No.Method & Description
    1int getLineNumber()This method gets the current line number.
    2void mark(int readAheadLimit)This method mark the present position in the stream.
    3int read()This method read a single character.
    4int read(char[] cbuf, int off, int len)This method read characters into a portion of an array.
    5String readLine()This method read a line of text.
    6void reset()This method reset the stream to the most recent mark.
    7void setLineNumber(int lineNumber)This method set the current line number.
    8long skip(long n)This method skip characters.

    Methods inherited

    This class inherits methods from the following classes −

    • Java.io.BufferedReader
    • Java.io.Reader
    • Java.io.Object

  • LineNumberInputStream 

    Introduction

    The Java.io.LineNumberInputStream class is an input stream filter that provides the added functionality of keeping track of the current line number. A line is a sequence of bytes ending with a carriage return character (‘\r’), a newline character (‘\n’), or a carriage return character followed immediately by a linefeed character.

    Class declaration

    Following is the declaration for Java.io.LineNumberInputStream class −

    public class LineNumberInputStream
   extends Reader

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    Field

    Following are the fields for Java.io.LineNumberInputStream class −

    • protected InputStream in − This is the input stream to be filtered.

    Class constructors

    Sr.No.Constructor & Description
    1LineNumberInputStream(InputStream in)This constructs a newline number input stream that reads its input from the specified input stream.

    Class methods

    Sr.No.Method & Description
    1int available()This method returns the number of bytes that can be read from this input stream without blocking.
    2int getLineNumber()This method returns the current line number.
    3void mark(int readlimit)This method marks the current position in this input stream.
    4int read()This method reads the next byte of data from this input stream.
    5int read(byte[] b, int off, int len)This method reads up to len bytes of data from this input stream into an array of bytes.
    6void reset()This method repositions this stream to the position at the time the mark method was last called on this input stream.
    7void setLineNumber(int lineNumber)This method sets the line number to the specified argument.
    8long skip(long n)This method skips over and discards n bytes of data from this input stream.

    Methods inherited

    This class inherits methods from the following classes −

    • Java.io.FilterInputStream
    • Java.io.Object

  • InputStreamReader 

    Introduction

    The Java.io.InputStreamReader class is a bridge from byte streams to character streams.It reads bytes and decodes them into characters using a specified charset.

    Class declaration

    Following is the declaration for Java.io.InputStreamReader class −

    public class InputStreamReader
   extends Reader

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    Field

    Following are the fields for Java.io.InputStreamReader class −

    • protected Object lock − This is the object used to synchronize operations on this stream.

    Class constructors

    Sr.No.Constructor & Description
    1InputStreamReader(InputStream in)This creates an InputStreamReader that uses the default charset.
    2InputStreamReader(InputStream in, Charset cs)This creates an InputStreamReader that uses the given charset.
    3InputStreamReader(InputStream in, CharsetDecoder dec)This creates an InputStreamReader that uses the given charset decoder.
    4InputStreamReader(InputStream in, String charsetName)This creates an InputStreamReader that uses the named charset.

    Class methods

    Sr.No.Method & Description
    1void close()This method closes the stream and releases any system resources associated with it.
    2String getEncoding()This method returns the name of the character encoding being used by this stream.
    3int read()This method reads a single character.
    4int read(char[] cbuf, int offset, int length)This method reads characters into a portion of an array.
    5boolean ready()This method tells whether this stream is ready to be read.

    Methods inherited

    This class inherits methods from the following classes −

    • Java.io.Reader
    • Java.io.Object

  • InputStream 

    Introduction

    The Java.io.InputStream class is the superclass of all classes representing an input stream of bytes. Applications that need to define a subclass of InputStream must always provide a method that returns the next byte of input.

    Class declaration

    Following is the declaration for Java.io.InputStream class −

    public abstract class InputStream
   extends Object

      implements Closeable

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    Class constructors

    Sr.No.Constructor & Description
    1InputStream()Single Constructor

    Class methods

    Sr.No.Method & Description
    1int available()This method returns an estimate of the number of bytes that can be read (or skipped over) from this input stream without blocking by the next invocation of a method for this input stream.
    2void close()This method closes this input stream and releases any system resources associated with the stream.
    3void mark(int readlimit)This method marks the current position in this input stream.
    4boolean markSupported()This method tests if this input stream supports the mark and reset methods.
    5abstract int read()This method reads the next byte of data from the input stream.
    6int read(byte[] b)This method reads some number of bytes from the input stream and stores them into the buffer array b.
    7int read(byte[] b, int off, int len) <This method reads up to len bytes of data from the input stream into an array of bytes.
    8void reset()This method repositions this stream to the position at the time the mark method was last called on this input stream.
    9long skip(long n)This method skips over and discards n bytes of data from this input stream.

    Methods inherited

    This class inherits methods from the following classes −

    • Java.io.Object

  • FilterWriter 

    Introduction

    The Java.io.FilterWriter class is for writing filtered character streams. Following are the important points about FilterWriter −

    • The class itself provides default methods that pass all requests to the contained stream.
    • The Subclasses of FilterWriter should override some of these methods and may also provide additional methods and fields.

    Class declaration

    Following is the declaration for Java.io.FilterWriter class −

    public abstract class FilterWriter
   extends Writer

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    Field

    Following are the fields for Java.io.FilterWriter class −

    • protected Writer in − This is the character-output stream.
    • protected Object lock − This is the object used to synchronize operations on this stream.

    Class constructors

    Sr.No.Constructor & Description
    1protected FilterWriter(Writer in)This creates a new filtered writer.

    Class methods

    Sr.No.Method & Description
    1void close()This method flushes the stream.
    2void flush()This method flushes the stream.
    3void write(char[] cbuf, int off, int len)This method writes a portion of an array of characters.
    4void write(int c)This method writes a single character.
    5void write(String str, int off, int len)This method writes a portion of a string.

    Methods inherited

    This class inherits methods from the following classes −

    • Java.io.Writer
    • Java.io.Object