Java - StringReader class

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Introduction

The Java StringReader class is a character stream whose source is a string.

Class declaration

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

public class StringReader
   extends Reader

Field

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

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

Class constructors

Class methods

Methods inherited

This class inherits methods from the following classes −

• Java.io.Reader
• Java.io.Object

Example - Properly closing a StringReader

The following example shows the usage of StringReader close() method.

StringReaderDemo.java

package com.tutorialspoint;

import java.io.StringReader;
import java.io.IOException;

public class StringReaderDemo {
   public static void main(String[] args) throws IOException {
      StringReader reader = new StringReader("Hello, world!");

      int data = reader.read();
      System.out.println("First character: " + (char) data);

      reader.close(); // closing the reader
      System.out.println("Reader closed.");
   }
}

Output

Let us compile and run the above program, this will produce the following result−

First character: H
Reader closed.

Explanation

• The reader reads one character successfully.

• Then it's closed using close().

• No error occurs because we don't attempt to read after closing.

Example - Basic use of mark() and reset()

The following example shows the usage of StringReader mark(int readAheadLimit) method.

StringReaderDemo.java

package com.tutorialspoint;

import java.io.StringReader;

public class StringReaderDemo {
   public static void main(String[] args) throws Exception {
      StringReader reader = new StringReader("abcdef");

      System.out.print((char) reader.read()); // a
      reader.mark(3); // mark at position after 'a'

      System.out.print((char) reader.read()); // b
      System.out.print((char) reader.read()); // c

      reader.reset(); // go back to mark (before 'b')

      System.out.print((char) reader.read()); // b
      System.out.print((char) reader.read()); // c

      reader.close();
   }
}

Output

Let us compile and run the above program, this will produce the following result−

abcbc

Explanation

• You read 'a', then mark the position.

• Then read 'b' and 'c'.

• After reset(), you go back to the position after 'a' and read 'b' and 'c' again.

Example - Checking if mark() is supported

The following example shows the usage of StringReader markSupported() method.

StringReaderDemo.java

package com.tutorialspoint;

import java.io.StringReader;

public class StringReaderDemo {
   public static void main(String[] args) {
      StringReader reader = new StringReader("Hello, world!");

      System.out.println("Mark supported? " + reader.markSupported());

      reader.close();
   }
}

Output

Let us compile and run the above program, this will produce the following result−

Mark supported? true

Explanation

• This example simply checks if the StringReader supports marking (it does).

• You can safely use mark() and reset() on this reader.