Java - CharArrayWriter Class

Introduction

The Java CharArrayWriter class implements a character buffer that can be used as an Writer. The buffer automatically grows when data is written to the stream.

Class declaration

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

public class CharArrayWriter
   extends Writer

Field

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

• protected char[] buf − This is the buffer where data is stored.

• protected int count − This is the number of chars in the buffer.

• 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.Writer
• Java.io.Object

Example - Appending a Single Character to a CharArrayWriter

The following example shows the usage of Java CharArrayWriter append(char c) method.

CharArrayWriterDemo.java

package com.tutorialspoint;

import java.io.CharArrayWriter;

public class CharArrayWriterDemo {
   public static void main(String[] args) {
      // Creating a CharArrayWriter instance
      CharArrayWriter charArrayWriter = new CharArrayWriter();

      // Appending characters one by one
      charArrayWriter.append('H');
      charArrayWriter.append('i');
      charArrayWriter.append('!');

      // Converting the CharArrayWriter content to a string and displaying it
      System.out.println("CharArrayWriter content: " + charArrayWriter.toString());

      // Closing the CharArrayWriter (not necessary, but good practice)
      charArrayWriter.close();
   }
}

Output

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

CharArrayWriter content: Hi!

Explanation

• A CharArrayWriter object is created.

• The append(char c) method is used to append individual characters: 'H', 'i', and '!'.

• The toString() method is called to retrieve and print the content stored in the CharArrayWriter.

Example - Appending a Subsequence from a StringBuilder

The following example shows the usage of Java CharArrayWriter append(CharSequence csq, int start, int end) method.

CharArrayWriterDemo.java

package com.tutorialspoint;

import java.io.CharArrayWriter;

public class CharArrayWriterDemo {
   public static void main(String[] args) {
      CharArrayWriter writer = new CharArrayWriter();

      // Create a StringBuilder
      StringBuilder sb = new StringBuilder("Spring Boot Framework");

      // Append a substring from index 7 to 11 ("Boot")
      writer.append(sb, 7, 11);

      // Append another substring from index 12 to 21 ("Framework")
      writer.append(sb, 12, 21);

      // Print the output
      System.out.println(writer.toString()); // Output: BootFramework
   }
}

Output

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

BootFramework

Explanation

• A StringBuilder "Spring Boot Framework" is created.

• The append method extracts "Boot" (index 7 to 11) and appends it.

• Another call extracts "Framework" (index 12 to 21) and appends it.

• The final output is "BootFramework".

Example - Closing a CharArrayWriter and Writing Data After Closing

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

CharArrayWriterDemo.java

package com.tutorialspoint;

import java.io.CharArrayWriter;
import java.io.IOException;

public class CharArrayWriterDemo {
   public static void main(String[] args) throws IOException {
      CharArrayWriter writer = new CharArrayWriter();

      // Write data to CharArrayWriter
      writer.write("Hello, Java!");

      // Close the writer
      writer.close();

      // Append more data after closing (allowed)
      writer.append(" Still working!");

      // Convert to string and print
      System.out.println(writer.toString()); // Output: Hello, Java! Still working!
   }
}

Output

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

Hello, Java! Still working!

Explanation

• A CharArrayWriter object is created.

• "Hello, Java!" is written to it.

• close() is called, but it does not affect further operations.

• " Still working!" is appended even after closing.

• The final output is "Hello, Java! Still working!".