Java Tutorial/File/CharBuffer

Buffer Equality

import java.nio.CharBuffer;
public class MainClass {
  public static void main(String[] args) {
    CharBuffer cb1 = CharBuffer.allocate(5), cb2 = CharBuffer.allocate(5);
    cb1.put("B").put("u").put("f").put("f").put("A");
    cb2.put("B").put("u").put("f").put("f").put("B");
    cb1.rewind();
    cb2.rewind();
    System.out.println(cb1.limit(4).equals(cb2.limit(4)));
  }
}
//

true

Buffer slice

import java.nio.CharBuffer;
public class MainClass {
  public static void main(String[] argv) throws Exception {
    CharBuffer buffer = CharBuffer.allocate(8);
    buffer.position(3).limit(5);
    CharBuffer sliceBuffer = buffer.slice();
    println(buffer);
    println(sliceBuffer);
    char[] myBuffer = new char[100];
    CharBuffer cb = CharBuffer.wrap(myBuffer);
    cb.position(12).limit(21);
    CharBuffer sliced = cb.slice();
    println(cb);
    println(sliced);
  }
  private static void println(CharBuffer cb) {
    System.out.println("pos=" + cb.position() + ", limit=" + cb.limit() + ", capacity="
        + cb.capacity() + ", arrayOffset=" + cb.arrayOffset());
  }
}
/*
*/

pos=3, limit=5, capacity=8, arrayOffset=0
pos=0, limit=2, capacity=2, arrayOffset=3
pos=12, limit=21, capacity=100, arrayOffset=0
pos=0, limit=9, capacity=9, arrayOffset=12

CharBuffer warps a ByteBuffer

import java.nio.ByteBuffer;
import java.nio.CharBuffer;
public class MainClass {
  public static void main(String argv[]) {
    ByteBuffer bb = ByteBuffer.allocate(100);
    bb.mark();
    bb.position(5);
    bb.reset();
    bb.mark().position(5).reset();
    char[] myBuffer = new char[100];
    CharBuffer cb = CharBuffer.wrap(myBuffer);
    cb.position(12).limit(21);
    CharBuffer sliced = cb.slice();
    System.out
        .println("Sliced: offset=" + sliced.arrayOffset() + ", capacity=" + sliced.capacity());
  }
}
//

Sliced: offset=12, capacity=9

Convert ByteBuffer to a CharBuffer

import java.nio.ByteBuffer;
import java.nio.CharBuffer;
public class MainClass {
  public static void main(String[] args) {
    ByteBuffer bb = ByteBuffer.wrap(new byte[] { 0, 0, 0, 0, 0, 0, 0, "a" });
    bb.rewind();
    CharBuffer cb = ((ByteBuffer) bb.rewind()).asCharBuffer();
    System.out.println("Char Buffer");
    while (cb.hasRemaining())
      System.out.println(cb.position() + " -> " + cb.get());
  }
}

Convert ByteBuffer to CharBuffer

import java.nio.Buffer;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.CharBuffer;
/**
 * Test asCharBuffer view.
 */
public class MainClass {
  public static void main(String[] argv) throws Exception {
    ByteBuffer byteBuffer = ByteBuffer.allocate(7).order(ByteOrder.BIG_ENDIAN);
    CharBuffer charBuffer = byteBuffer.asCharBuffer();
    byteBuffer.put(0, (byte) 0);
    byteBuffer.put(1, (byte) "H");
    byteBuffer.put(2, (byte) 0);
    byteBuffer.put(3, (byte) "i");
    byteBuffer.put(4, (byte) 0);
    byteBuffer.put(5, (byte) "!");
    byteBuffer.put(6, (byte) 0);
    println(byteBuffer);
    println(charBuffer);
    // now slice it differently
    byteBuffer.position(4);
    charBuffer = byteBuffer.asCharBuffer();
    println(byteBuffer);
    println(charBuffer);
  }
  // Print info about a buffer
  private static void println(Buffer buffer) {
    System.out.println("pos=" + buffer.position() + ", limit=" + buffer.limit() + ", capacity="
        + buffer.capacity() + ": "" + buffer.toString() + """);
  }
}
/*
*/

pos=0, limit=7, capacity=7: "java.nio.HeapByteBuffer[pos=0 lim=7 cap=7]"
pos=0, limit=3, capacity=3: "Hi!"
pos=4, limit=7, capacity=7: "java.nio.HeapByteBuffer[pos=4 lim=7 cap=7]"
pos=0, limit=1, capacity=1: "!"

Create a CharBuffer and put in some string

import java.nio.CharBuffer;
public class MainClass {
  public static void main(String[] argv) throws Exception {
    CharBuffer cb = CharBuffer.allocate(100);
    cb.put("This is a test String");
    cb.flip();
    // This throws an IllegalArgumentException
    cb.put(cb);
    System.out.println(cb);
  }
}

Fill String to CharBuffer

import java.nio.CharBuffer;
/**
 * Buffer fill/drain example. This code uses the simplest means of filling and
 * draining a buffer: one element at a time.
 */
public class MainClass {
  public static void main(String[] argv) throws Exception {
    CharBuffer buffer = CharBuffer.allocate(100);
    String string = "asdf";
    for (int i = 0; i < string.length(); i++) {
      buffer.put(string.charAt(i));
    }
    buffer.flip();
    drainBuffer(buffer);
    buffer.clear();
  }
  private static void drainBuffer(CharBuffer buffer) {
    while (buffer.hasRemaining()) {
      System.out.print(buffer.get());
    }
    System.out.println("");
  }
}

Flip a CharBuffer

import java.nio.CharBuffer;
public class MainClass {
  public static void main(String[] argv) throws Exception {
    char[] chars = new char[60];
    CharBuffer cb = CharBuffer.wrap(chars, 12, 42);
    println(cb);
    cb.put("This is a test String");
    cb.flip();
    println(cb);
    cb.clear();
    cb.put("Foobar");
    println(cb);
    for (int i = 0; i < 20; i++) {
      System.out.println("[" + i + "] = " + chars[i]);
    }
  }
  private static void println(CharBuffer cb) {
    System.out.println("pos=" + cb.position() + ", limit=" + cb.limit() + ", capacity="
        + cb.capacity() + ", arrayOffset=" + cb.arrayOffset());
  }
}
/*
*/

pos=12, limit=54, capacity=60, arrayOffset=0
pos=0, limit=33, capacity=60, arrayOffset=0
pos=6, limit=60, capacity=60, arrayOffset=0
[0] = F
[1] = o
[2] = o
[3] = b
[4] = a
[5] = r
...

Get array out of CharBuffer

import java.nio.CharBuffer;
public class MainClass {
  public static void main(String[] argv) throws Exception {
    CharBuffer cb = CharBuffer.allocate(100);
    cb.put("This is a test String");
    cb.flip();
    System.out.println("hasArray() = " + cb.hasArray());
    char[] carray = cb.array();
    System.out.print("array=");
    for (int i = 0; i < carray.length; i++) {
      System.out.print(carray[i]);
    }
    System.out.println("");
    System.out.flush();
  }
}
/**/

hasArray() = true
array=This is a test String

Save and read text using FileChannel with CharBuffer

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
public class MainClass {
  public static void main(String[] args) throws Exception {
    FileChannel fc = new FileOutputStream("data2.txt").getChannel();
    ByteBuffer buff = ByteBuffer.allocate(24); // More than needed
    buff.asCharBuffer().put("Some text");
    fc.write(buff);
    fc.close();
    fc = new FileInputStream("data2.txt").getChannel();
    buff.clear();
    fc.read(buff);
    buff.flip();
    System.out.println(buff.asCharBuffer());
  }
}
/*  */

Some text

Test buffer duplication

import java.nio.CharBuffer;
/**
 * Test buffer duplication.
 */
public class MainClass {
  public static void main(String[] argv) throws Exception {
    CharBuffer buffer = CharBuffer.wrap("01234567");
    buffer.position(3).limit(6).mark().position(5);
    CharBuffer dupeBuffer = buffer.duplicate();
    buffer.clear();
    println(buffer);
    println(dupeBuffer);
    dupeBuffer.reset();
    println(dupeBuffer);
    dupeBuffer.clear();
    println(dupeBuffer);
  }
  private static void println(CharBuffer cb) {
    System.out.println("pos=" + cb.position() + ", limit=" + cb.limit() + ", capacity="
        + cb.capacity() + ": "" + cb + """);
  }
}
/**/

pos=0, limit=8, capacity=8: "01234567"
pos=5, limit=6, capacity=8: "5"
pos=3, limit=6, capacity=8: "345"
pos=0, limit=8, capacity=8: "01234567"

Test the effects of buffer flipping

import java.nio.CharBuffer;
/**
 * Test the effects of buffer flipping.
 * 
 */
public class MainClass {
  public static void main(String[] argv) throws Exception {
    CharBuffer cb = CharBuffer.allocate(15);
    cb.put("Hello World");
    println(cb);
    cb.flip();
    println(cb);
    cb.flip();
    println(cb);
  }
  private static void println(CharBuffer cb) {
    System.out.println("pos=" + cb.position() + ", limit=" + cb.limit() + ": "" + cb + """);
  }
}

Use CharBuffer

import java.nio.ByteBuffer;
import java.nio.CharBuffer;
public class MainClass {
  private static void symmetricScramble(CharBuffer buffer) {
    while (buffer.hasRemaining()) {
      buffer.mark();
      char c1 = buffer.get();
      char c2 = buffer.get();
      buffer.reset();
      buffer.put(c2).put(c1);
    }
  }
  public static void main(String[] args) {
    char[] data = "UsingBuffers".toCharArray();
    ByteBuffer bb = ByteBuffer.allocate(data.length * 2);
    CharBuffer cb = bb.asCharBuffer();
    cb.put(data);
    System.out.println(cb.rewind());
    symmetricScramble(cb);
    System.out.println(cb.rewind());
    symmetricScramble(cb);
    System.out.println(cb.rewind());
  }
}
/*
*/

UsingBuffers
sUniBgfuefsr
UsingBuffers

Use while loop to read a CharBuffer

import java.nio.ByteBuffer;
import java.nio.CharBuffer;
public class MainClass {
  public static void main(String[] args) {
    ByteBuffer bb = ByteBuffer.wrap(new byte[] { 0, 0, 0, 0, 0, 0, 0, "a" });
    bb.rewind();
    CharBuffer cb = ((ByteBuffer) bb.rewind()).asCharBuffer();
    System.out.println("Char Buffer");
    while (cb.hasRemaining())
      System.out.println(cb.position() + " -> " + cb.get());
  }
}

Wrap a char array to a CharBuffer

import java.nio.CharBuffer;
public class MainClass {
  public static void main(String[] argv) throws Exception {
    CharBuffer buffer = CharBuffer.allocate(8);
    buffer.position(3).limit(5);
    CharBuffer sliceBuffer = buffer.slice();
    println(buffer);
    println(sliceBuffer);
    char[] myBuffer = new char[100];
    CharBuffer cb = CharBuffer.wrap(myBuffer);
    cb.position(12).limit(21);
    CharBuffer sliced = cb.slice();
    println(cb);
    println(sliced);
  }
  private static void println(CharBuffer cb) {
    System.out.println("pos=" + cb.position() + ", limit=" + cb.limit() + ", capacity="
        + cb.capacity() + ", arrayOffset=" + cb.arrayOffset());
  }
}
/*
*/

pos=3, limit=5, capacity=8, arrayOffset=0
pos=0, limit=2, capacity=2, arrayOffset=3
pos=12, limit=21, capacity=100, arrayOffset=0
pos=0, limit=9, capacity=9, arrayOffset=12