demo_code.java

    /**
     * Deletes the character at the specified index.
     *
     * @see #charAt(int)
     * @see #setCharAt(int, char)
     * @param index  the index to delete
     * @return this, to enable chaining
     * @throws IndexOutOfBoundsException if the index is invalid
     */
    public StrBuilder deleteCharAt(int index) {
        if (index < 0 || index >= size) {
            throw new StringIndexOutOfBoundsException(index);
        }
        deleteImpl(index, index + 1, 1);
        return this;
    }

    //-----------------------------------------------------------------------
    /**
     * Copies the builder's character array into a new character array.
     * 
     * @return a new array that represents the contents of the builder
     */
    public char[] toCharArray() {
        if (size == 0) {
            return ArrayUtils.EMPTY_CHAR_ARRAY;
        }
        char chars[] = new char[size];
        System.arraycopy(buffer, 0, chars, 0, size);
        return chars;
    }

    /**
     * Appends a separator to the builder if the loop index is greater than zero.
     * The separator is appended using {@link #append(char)}.
     * <p>
     * This method is useful for adding a separator each time around the
     * loop except the first.
     * <pre>
     * for (int i = 0; i < list.size(); i++) {
     *   appendSeparator(",", i);
     *   append(list.get(i));
     * }
     * </pre>
     * Note that for this simple example, you should use
     * {@link #appendWithSeparators(Iterable, String)}.
     * 
     * @param separator  the separator to use
     * @param loopIndex  the loop index
     * @return this, to enable chaining
     * @since 2.3
     */
    public StrBuilder appendSeparator(char separator, int loopIndex) {
        if (loopIndex > 0) {
            append(separator);
        }
        return this;
    }

    //-----------------------------------------------------------------------
    /**
     * Appends the pad character to the builder the specified number of times.
     * 
     * @param length  the length to append, negative means no append
     * @param padChar  the character to append
     * @return this, to enable chaining
     */
    public StrBuilder appendPadding(int length, char padChar) {
        if (length >= 0) {
            ensureCapacity(size + length);
            for (int i = 0; i < length; i++) {
                buffer[size++] = padChar;
            }
        }
        return this;
    }


    /**
     * Appends an object to the builder padding on the right to a fixed length.
     * The <code>toString</code> of the object is used.
     * If the object is larger than the length, the right hand side is lost.
     * If the object is null, null text value is used.
     * 
     * @param obj  the object to append, null uses null text
     * @param width  the fixed field width, zero or negative has no effect
     * @param padChar  the pad character to use
     * @return this, to enable chaining
     */
    public StrBuilder appendFixedWidthPadRight(Object obj, int width, char padChar) {
        if (width > 0) {
            ensureCapacity(size + width);
            String str = (obj == null ? getNullText() : obj.toString());
            int strLen = str.length();
            if (strLen >= width) {
                str.getChars(0, width, buffer, size);
            } else {
                int padLen = width - strLen;
                str.getChars(0, strLen, buffer, size);
                for (int i = 0; i < padLen; i++) {
                    buffer[size + strLen + i] = padChar;
                }
            }
            size += width;
        }
        return this;
    }
    /**
     * Appends an object to the builder padding on the right to a fixed length.
     * The <code>String.valueOf</code> of the <code>int</code> value is used.
     * If the object is larger than the length, the right hand side is lost.
     * 
     * @param value  the value to append
     * @param width  the fixed field width, zero or negative has no effect
     * @param padChar  the pad character to use
     * @return this, to enable chaining
     */
    public StrBuilder appendFixedWidthPadRight(int value, int width, char padChar) {
        return appendFixedWidthPadRight(String.valueOf(value), width, padChar);
    }