Introduction
The Java.io PushbackReader is a class used to unread data, to push back characters into stream. The main functionality of this is to interpret the present character into the reader.
If the unread() method is called then, it pushes the data into the push back reader. After again calling read() method at that time the push backed data will reads first. The last pushed character will be reads first. The push back data limit is also initialized with constructor in push back reader.
Declaration
Java.io PushbackReader class is declared below:
Public class PushbackReader extends FilterReader Fields
Java.io PushbackReader class fields are:
- Protected Reader in : The field represents the input stream have to read.
- Protected Object Lock : For synchronize operations this object is used in PushBackReader.
Table
| Constructor | Description |
|---|---|
| PushBackReader (Reader in) | The function of this constructor is to create the push back reader instance and used to read character into buffer. |
| PushBackReader (Reader in, int size) | The function of this constructor is to create the push back reader instance and used to read character into the represented size of buffer. |
Table
| Method | Description |
|---|---|
| void close () | The function of this method is to close the present stream and associated to input stream systems resources are released. |
| Boolean markSupported () | The function of this method is to check the represented mark method is supported by this stream or not. |
| void unread(char[] cbuf, int off, int n) | The function of this method is to push back the specified length of array of characters from the stream and copied into push back buffer. |
| void unread(char[] cbuf) | The function of this method is to push back the characters and copied into push back buffer. |
Description
From the following classes, methods are inherited to the push back reader class.
- Java.io.Object
- Java.io.Reader
Examples
Usage of void unread(char[] cbuf) method.
[c]import java.io.*;
public class PushbackReader
{
public static void main(String[] args) {
String s = "SPLESSONS";
// creating a new String reader instance
StringReader sr = new StringReader(s);
// creating a new Push back reader based on string reader
PushbackReader pr = new PushbackReader(sr, 20);
try {
// To read the characters
for (int i = 0; i < 9; i++) {
char c = (char) pr.read();
System.out.print("" + c);
}
// To change line
System.out.println();
// creating a new array to unread
char cbuf[] = {'w', 'o', 'r', 'l', 'd'};
// unread into character buffer
pr.unread(cbuf);
// To read five characters, which is what we unread from cbuf
for (int i = 0; i < 5; i++) {
char c = (char) pr.read();
System.out.print("" + c);
}
// To close the stream
pr.close();
} catch (IOException ex) {
ex.printStackTrace();
}
}
}[/c]
Output
The result will be as follows.
[c]
SPLESSONS
world
[/c]
Usage of Boolean markSupported () method.
[c]import java.io.*;
public class PushbackReader
{
public static void main(String[] args)
{
String s = "SPLESSONS";
// creating a new String reader instance
StringReader sr = new StringReader(s);
// creating a new Push back reader based on the string reader
PushbackReader pr = new PushbackReader(sr, 20);
try {
// To read the given characters
for (int i = 0; i < 9; i++) {
char c = (char) pr.read();
System.out.print("" + c);
}
// To change line
System.out.println();
// To close the stream
pr.close();
System.out.println("Stream closed.");
} catch (IOException ex) {
ex.printStackTrace();
}
}
}[/c]
Output
The result will be as follows.
[c]
SPLESSONS
Stream closed.
[/c]
Key Points
- TheJava.io PushbackReader is a class used to unread data i.e., to push back characters into stream.
- The main functionality of this is to interpret the present character into the reader.
- When the unread() method is called then, it pushes the data into the push back reader.
- The last pushed character will be reads first. The push back data limit is also initialized with constructor in Java.io PushbackReader.