A new class -->String

[jinheking]

I want to make a Class like java's String Class.
module jdk2d.lang;

import std.stdio;
/*
* The <code>String</code> class represents character strings. All
* string literals in D programs, such as <code>"abc"</code>, are
* implemented as instances of this class.
* @author  Caoqi
* @version 0.001, 07/03/30
* @since   JDK2D 0.02
* @url     http://jinheking.javaeye.com/admin
* <p>
*/

public class  String{
  private final wchar[] value;

  /** The offset is the first index of the storage that is used. */
  private final int offset;

  /** The count is the number of characters in the String. */
  private final int count;

  /*
   * Initializes a newly created {@code String} object so that it represents
   * an empty character sequence.  Note that use of this constructor is
   * unnecessary since Strings are immutable.
   */
  this(){
   this.offset = 0;
   this.count = 0;
   this.value = new wchar[0];
  }

  String opAssign(wchar[] value) {
   int size = value.length;
   offset = 0;
   count = size;
   value = value;
   return this;
    }

  /*
     * Allocates a new {@code String} so that it represents the sequence of
     * characters currently contained in the character array argument. The
     * contents of the character array are copied; subsequent modification 
of
     * the character array does not affect the newly created string.
     *
     * @param  value
     *         The initial value of the string
     */
    public this(wchar[] value) {
   int size = value.length;
   this.offset = 0;
   this.count = size;
   this.value = value;
    }

  /**
     * Returns the length of this string.
     * The length is equal to the number of <a 
href="Character.html#unicode">Unicode
     * code units</a> in the string.
     *
     * @return  the length of the sequence of characters represented by this
     *          object.
     */
    public int length() {
        return count;
    }

    /**
     * Returns <tt>true</tt> if, and only if, {@link #length()} is 
<tt>0</tt>.
     *
     * @return <tt>true</tt> if {@link #length()} is <tt>0</tt>, otherwise
     * <tt>false</tt>
     *
     * @since JDK2D 0.01
     */
    public bool isEmpty() {
    return count == 0;
    }
  /**
     * Returns the index within this string of the first occurrence of the
     * specified substring. The integer returned is the smallest value
     * <i>k</i> such that:
     * <blockquote><pre>
     * this.startsWith(str, <i>k</i>)
     * </pre></blockquote>
     * is <code>true</code>.
     *
     * @param   str   any string.
     * @return  if the string argument occurs as a substring within this
     *          object, then the index of the first character of the first
     *          such substring is returned; if it does not occur as a
     *          substring, <code>-1</code> is returned.
     */

    public int indexOf(String str) {
   return indexOf(str, 0);
    }

    public int indexOf(wchar[] str) {
   return indexOf(str, 0);
    }

    /**
     * Returns the index within this string of the first occurrence of the
     * specified substring, starting at the specified index.  The integer
     * returned is the smallest value <tt>k</tt> for which:
     * <blockquote><pre>
     *     k &gt;= Math.min(fromIndex, this.length()) && 
this.startsWith(str, k)
     * </pre></blockquote>
     * If no such value of <i>k</i> exists, then -1 is returned.
     *
     * @param   str         the substring for which to search.
     * @param   fromIndex   the index from which to start the search.
     * @return  the index within this string of the first occurrence of the
     *          specified substring, starting at the specified index.
     */
    public int indexOf(String str, int fromIndex) {
        return indexOf(value, offset, count,
                       str.value, str.offset, str.count, fromIndex);
    }

    public int indexOf(wchar[] wstr, int fromIndex) {
       String str=new String(wstr);
        return indexOf(value, offset, count,
                       str.value, str.offset, str.count, fromIndex);
    }

    /**
     * Code shared by String and StringBuffer to do searches. The
     * source is the character array being searched, and the target
     * is the string being searched for.
     *
     * @param   source       the characters being searched.
     * @param   sourceOffset offset of the source string.
     * @param   sourceCount  count of the source string.
     * @param   target       the characters being searched for.
     * @param   targetOffset offset of the target string.
     * @param   targetCount  count of the target string.
     * @param   fromIndex    the index to begin searching from.
     */
    static int indexOf(wchar[] source, int sourceOffset, int sourceCount,
                       wchar[] target, int targetOffset, int targetCount,
                       int fromIndex) {
   if (fromIndex >= sourceCount) {
              return (targetCount == 0 ? sourceCount : -1);
   }
       if (fromIndex < 0) {
           fromIndex = 0;
       }
   if (targetCount == 0) {
       return fromIndex;
   }

          wchar first  = target[targetOffset];
          int max = sourceOffset + (sourceCount - targetCount);

          for (int i = sourceOffset + fromIndex; i <= max; i++) {
              /* Look for first character. */
              if (source[i] != first) {
                i++;
                  while (i <= max && source[i] != first){
                   i++;
                  }
              }

              /* Found first character, now look at the rest of v2 */
              if (i <= max) {
                  int j = i + 1;
                  int end = j + targetCount - 1;
                  for (int k = targetOffset + 1; j < end && (source[j] == 
target[k]);j++){
                    k++;
                  }

                  if (j == end) {
                      /* Found whole string. */
                      return i - sourceOffset;
                  }
              }
          }
          return -1;
      }

 char[] toString(){
  return cast(char[])std.utf.toUTF8(this.value);
 }
}

public static void  main() {
   String str = new String("The quick brown fox jumped over the lazy dog.");
   String s1 = new String("abc");
   s1="abc";
   writefln(s1);
   printf("%d\n",str.indexOf("z"));
   printf("%d\n",str.isEmpty());
}