src/java.base/share/classes/java/lang/AbstractStringBuilder.java

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@@ -29,10 +29,16 @@
 import java.util.Arrays;
 import java.util.Spliterator;
 import java.util.stream.IntStream;
 import java.util.stream.StreamSupport;
 
+import static java.lang.String.COMPACT_STRINGS;
+import static java.lang.String.UTF16;
+import static java.lang.String.LATIN1;
+import static java.lang.String.checkIndex;
+import static java.lang.String.checkOffset;
+
 /**
  * A mutable sequence of characters.
  * <p>
  * Implements a modifiable string. At any point in time it contains some
  * particular sequence of characters, but the length and content of the

@@ -49,11 +55,16 @@
  */
 abstract class AbstractStringBuilder implements Appendable, CharSequence {
     /**
      * The value is used for character storage.
      */
-    char[] value;
+    byte[] value;
+
+    /**
+     * The id of the encoding used to encode the bytes in {@code value}.
+     */
+    byte coder;
 
     /**
      * The count is the number of characters used.
      */
     int count;

@@ -66,11 +77,17 @@
 
     /**
      * Creates an AbstractStringBuilder of the specified capacity.
      */
     AbstractStringBuilder(int capacity) {
-        value = new char[capacity];
+        if (COMPACT_STRINGS) {
+            value = new byte[capacity];
+            coder = LATIN1;
+        } else {
+            value = StringUTF16.newBytesFor(capacity);
+            coder = UTF16;
+        }
     }
 
     /**
      * Returns the length (character count).
      *

@@ -88,11 +105,11 @@
      * will occur.
      *
      * @return  the current capacity
      */
     public int capacity() {
-        return value.length;
+        return value.length >> coder;
     }
 
     /**
      * Ensures that the capacity is at least equal to the specified minimum.
      * If the current capacity is less than the argument, then a new internal

@@ -108,50 +125,76 @@
      * actual capacity below that requested here.
      *
      * @param   minimumCapacity   the minimum desired capacity.
      */
     public void ensureCapacity(int minimumCapacity) {
-        if (minimumCapacity > 0)
+        if (minimumCapacity > 0) {
             ensureCapacityInternal(minimumCapacity);
     }
+    }
 
     /**
      * This method has the same contract as ensureCapacity, but is
      * never synchronized.
      */
     private void ensureCapacityInternal(int minimumCapacity) {
         // overflow-conscious code
-        if (minimumCapacity - value.length > 0)
+        int capacity = value.length >> coder;
+        if (minimumCapacity - capacity > 0) {
             expandCapacity(minimumCapacity);
     }
+    }
 
     /**
      * This implements the expansion semantics of ensureCapacity with no
      * size check or synchronization.
      */
-    void expandCapacity(int minimumCapacity) {
-        int newCapacity = value.length * 2 + 2;
-        if (newCapacity - minimumCapacity < 0)
+    private void expandCapacity(int minimumCapacity) {
+        int newCapacity = (value.length >> coder) * 2 + 2;
+        if (newCapacity - minimumCapacity < 0) {
             newCapacity = minimumCapacity;
+        }
         if (newCapacity < 0) {
-            if (minimumCapacity < 0) // overflow
+            if (minimumCapacity < 0) {// overflow
                 throw new OutOfMemoryError();
+            }
             newCapacity = Integer.MAX_VALUE;
         }
-        value = Arrays.copyOf(value, newCapacity);
+        if (coder != LATIN1 && newCapacity > StringUTF16.MAX_LENGTH) {
+            if (minimumCapacity >= StringUTF16.MAX_LENGTH) {
+                throw new OutOfMemoryError();
+            }
+            newCapacity = StringUTF16.MAX_LENGTH;
+        }
+        this.value = Arrays.copyOf(value, newCapacity << coder);
+    }
+
+    /**
+     * If the coder is "isLatin1", this inflates the internal 8-bit storage
+     * to 16-bit <hi=0, low> pair storage.
+     */
+    private void inflate() {
+        if (!isLatin1()) {
+            return;
+        }
+        byte[] buf = StringUTF16.newBytesFor(value.length);
+        StringLatin1.inflateSB(value, buf, 0, count);
+        this.value = buf;
+        this.coder = UTF16;
     }
 
     /**
      * Attempts to reduce storage used for the character sequence.
      * If the buffer is larger than necessary to hold its current sequence of
      * characters, then it may be resized to become more space efficient.
      * Calling this method may, but is not required to, affect the value
      * returned by a subsequent call to the {@link #capacity()} method.
      */
     public void trimToSize() {
-        if (count < value.length) {
-            value = Arrays.copyOf(value, count);
+        int length = count << coder;
+        if (length < value.length) {
+            value = Arrays.copyOf(value, length);
         }
     }
 
     /**
      * Sets the length of the character sequence.

@@ -177,18 +220,21 @@
      * @param      newLength   the new length
      * @throws     IndexOutOfBoundsException  if the
      *               {@code newLength} argument is negative.
      */
     public void setLength(int newLength) {
-        if (newLength < 0)
+        if (newLength < 0) {
             throw new StringIndexOutOfBoundsException(newLength);
+        }
         ensureCapacityInternal(newLength);
-
         if (count < newLength) {
-            Arrays.fill(value, count, newLength, '\0');
+            if (isLatin1()) {
+                StringLatin1.fillNull(value, count, newLength);
+            } else {
+                StringUTF16.fillNull(value, count, newLength);
+            }
         }
-
         count = newLength;
     }
 
     /**
      * Returns the {@code char} value in this sequence at the specified index.

@@ -207,13 +253,15 @@
      * @throws     IndexOutOfBoundsException  if {@code index} is
      *             negative or greater than or equal to {@code length()}.
      */
     @Override
     public char charAt(int index) {
-        if ((index < 0) || (index >= count))
-            throw new StringIndexOutOfBoundsException(index);
-        return value[index];
+        checkIndex(index, count);
+        if (isLatin1()) {
+            return (char)(value[index] & 0xff);
+        }
+        return StringUTF16.charAt(value, index);
     }
 
     /**
      * Returns the character (Unicode code point) at the specified
      * index. The index refers to {@code char} values

@@ -234,14 +282,15 @@
      * @exception  IndexOutOfBoundsException  if the {@code index}
      *             argument is negative or not less than the length of this
      *             sequence.
      */
     public int codePointAt(int index) {
-        if ((index < 0) || (index >= count)) {
-            throw new StringIndexOutOfBoundsException(index);
+        checkIndex(index, count);
+        if (isLatin1()) {
+            return value[index] & 0xff;
         }
-        return Character.codePointAtImpl(value, index, count);
+        return StringUTF16.codePointAtSB(value, index, count);
     }
 
     /**
      * Returns the character (Unicode code point) before the specified
      * index. The index refers to {@code char} values

@@ -263,14 +312,17 @@
      *            argument is less than 1 or greater than the length
      *            of this sequence.
      */
     public int codePointBefore(int index) {
         int i = index - 1;
-        if ((i < 0) || (i >= count)) {
+        if (i < 0 || i >= count) {
             throw new StringIndexOutOfBoundsException(index);
         }
-        return Character.codePointBeforeImpl(value, index, 0);
+        if (isLatin1()) {
+            return value[i] & 0xff;
+        }
+        return StringUTF16.codePointBeforeSB(value, index);
     }
 
     /**
      * Returns the number of Unicode code points in the specified text
      * range of this sequence. The text range begins at the specified

@@ -293,11 +345,14 @@
      */
     public int codePointCount(int beginIndex, int endIndex) {
         if (beginIndex < 0 || endIndex > count || beginIndex > endIndex) {
             throw new IndexOutOfBoundsException();
         }
-        return Character.codePointCountImpl(value, beginIndex, endIndex - beginIndex);
+        if (isLatin1()) {
+            return endIndex - beginIndex;
+        }
+        return StringUTF16.codePointCountSB(value, beginIndex, endIndex);
     }
 
     /**
      * Returns the index within this sequence that is offset from the
      * given {@code index} by {@code codePointOffset} code

@@ -319,11 +374,11 @@
      */
     public int offsetByCodePoints(int index, int codePointOffset) {
         if (index < 0 || index > count) {
             throw new IndexOutOfBoundsException();
         }
-        return Character.offsetByCodePointsImpl(value, 0, count,
+        return Character.offsetByCodePoints(this,
                                                 index, codePointOffset);
     }
 
     /**
      * Characters are copied from this sequence into the

@@ -353,17 +408,18 @@
      *             {@code dst.length}
      *             </ul>
      */
     public void getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin)
     {
-        if (srcBegin < 0)
-            throw new StringIndexOutOfBoundsException(srcBegin);
-        if ((srcEnd < 0) || (srcEnd > count))
-            throw new StringIndexOutOfBoundsException(srcEnd);
-        if (srcBegin > srcEnd)
-            throw new StringIndexOutOfBoundsException("srcBegin > srcEnd");
-        System.arraycopy(value, srcBegin, dst, dstBegin, srcEnd - srcBegin);
+        checkRangeSIOOBE(srcBegin, srcEnd, count);  // compatible to old version
+        int n = srcEnd - srcBegin;
+        checkRange(dstBegin, dstBegin + n, dst.length);
+        if (isLatin1()) {
+            StringLatin1.getCharsSB(value, srcBegin, srcEnd, dst, dstBegin);
+        } else {
+            StringUTF16.getCharsSB(value, srcBegin, srcEnd, dst, dstBegin);
+        }
     }
 
     /**
      * The character at the specified index is set to {@code ch}. This
      * sequence is altered to represent a new character sequence that is

@@ -377,13 +433,19 @@
      * @param      ch      the new character.
      * @throws     IndexOutOfBoundsException  if {@code index} is
      *             negative or greater than or equal to {@code length()}.
      */
     public void setCharAt(int index, char ch) {
-        if ((index < 0) || (index >= count))
-            throw new StringIndexOutOfBoundsException(index);
-        value[index] = ch;
+        checkIndex(index, count);
+        if (isLatin1() && StringLatin1.canEncode(ch)) {
+            value[index] = (byte)ch;
+        } else {
+            if (isLatin1()) {
+                inflate();
+            }
+            StringUTF16.putCharSB(value, index, ch);
+        }
     }
 
     /**
      * Appends the string representation of the {@code Object} argument.
      * <p>

@@ -416,65 +478,74 @@
      *
      * @param   str   a string.
      * @return  a reference to this object.
      */
     public AbstractStringBuilder append(String str) {
-        if (str == null)
+        if (str == null) {
             return appendNull();
+        }
         int len = str.length();
         ensureCapacityInternal(count + len);
-        str.getChars(0, len, value, count);
+        putStringAt(count, str);
         count += len;
         return this;
     }
 
     // Documentation in subclasses because of synchro difference
     public AbstractStringBuilder append(StringBuffer sb) {
-        if (sb == null)
-            return appendNull();
-        int len = sb.length();
-        ensureCapacityInternal(count + len);
-        sb.getChars(0, len, value, count);
-        count += len;
-        return this;
+        return this.append((AbstractStringBuilder)sb);
     }
 
     /**
      * @since 1.8
      */
     AbstractStringBuilder append(AbstractStringBuilder asb) {
-        if (asb == null)
+        if (asb == null) {
             return appendNull();
+        }
         int len = asb.length();
         ensureCapacityInternal(count + len);
-        asb.getChars(0, len, value, count);
+        if (getCoder() != asb.getCoder()) {
+            inflate();
+        }
+        asb.getBytes(value, count, coder);
         count += len;
         return this;
     }
 
     // Documentation in subclasses because of synchro difference
     @Override
     public AbstractStringBuilder append(CharSequence s) {
-        if (s == null)
+        if (s == null) {
             return appendNull();
-        if (s instanceof String)
+        }
+        if (s instanceof String) {
             return this.append((String)s);
-        if (s instanceof AbstractStringBuilder)
+        }
+        if (s instanceof AbstractStringBuilder) {
             return this.append((AbstractStringBuilder)s);
-
+        }
         return this.append(s, 0, s.length());
     }
 
     private AbstractStringBuilder appendNull() {
-        int c = count;
-        ensureCapacityInternal(c + 4);
-        final char[] value = this.value;
-        value[c++] = 'n';
-        value[c++] = 'u';
-        value[c++] = 'l';
-        value[c++] = 'l';
-        count = c;
+        ensureCapacityInternal(count + 4);
+        int count = this.count;
+        byte[] val = this.value;
+        if (isLatin1()) {
+            val[count++] = 'n';
+            val[count++] = 'u';
+            val[count++] = 'l';
+            val[count++] = 'l';
+        } else {
+            checkOffset(count + 4, val.length >> 1);
+            StringUTF16.putChar(val, count++, 'n');
+            StringUTF16.putChar(val, count++, 'u');
+            StringUTF16.putChar(val, count++, 'l');
+            StringUTF16.putChar(val, count++, 'l');
+        }
+        this.count = count;
         return this;
     }
 
     /**
      * Appends a subsequence of the specified {@code CharSequence} to this

@@ -505,25 +576,17 @@
      *             {@code start} is greater than {@code end} or
      *             {@code end} is greater than {@code s.length()}
      */
     @Override
     public AbstractStringBuilder append(CharSequence s, int start, int end) {
-        if (s == null)
+        if (s == null) {
             s = "null";
-        if ((start < 0) || (start > end) || (end > s.length()))
-            throw new IndexOutOfBoundsException(
-                "start " + start + ", end " + end + ", s.length() "
-                + s.length());
+        }
+        checkRange(start, end, s.length());
         int len = end - start;
         ensureCapacityInternal(count + len);
-        if (s instanceof String) {
-            ((String)s).getChars(start, end, value, count);
-        } else {
-            for (int i = start, j = count; i < end; i++, j++)
-                value[j] = s.charAt(i);
-        }
-        count += len;
+        appendChars(s, start, end);
         return this;
     }
 
     /**
      * Appends the string representation of the {@code char} array

@@ -542,12 +605,11 @@
      * @return  a reference to this object.
      */
     public AbstractStringBuilder append(char[] str) {
         int len = str.length;
         ensureCapacityInternal(count + len);
-        System.arraycopy(str, 0, value, count, len);
-        count += len;
+        appendChars(str, 0, len);
         return this;
     }
 
     /**
      * Appends the string representation of a subarray of the

@@ -570,14 +632,14 @@
      * @throws IndexOutOfBoundsException
      *         if {@code offset < 0} or {@code len < 0}
      *         or {@code offset+len > str.length}
      */
     public AbstractStringBuilder append(char str[], int offset, int len) {
-        if (len > 0)                // let arraycopy report AIOOBE for len < 0
+        int end = offset + len;
+        checkRange(offset, end, str.length);
             ensureCapacityInternal(count + len);
-        System.arraycopy(str, offset, value, count, len);
-        count += len;
+        appendChars(str, offset, end);
         return this;
     }
 
     /**
      * Appends the string representation of the {@code boolean}

@@ -590,24 +652,43 @@
      *
      * @param   b   a {@code boolean}.
      * @return  a reference to this object.
      */
     public AbstractStringBuilder append(boolean b) {
+        ensureCapacityInternal(count + (b ? 4 : 5));
+        int count = this.count;
+        byte[] val = this.value;
+        if (isLatin1()) {
         if (b) {
-            ensureCapacityInternal(count + 4);
-            value[count++] = 't';
-            value[count++] = 'r';
-            value[count++] = 'u';
-            value[count++] = 'e';
-        } else {
-            ensureCapacityInternal(count + 5);
-            value[count++] = 'f';
-            value[count++] = 'a';
-            value[count++] = 'l';
-            value[count++] = 's';
-            value[count++] = 'e';
+                val[count++] = 't';
+                val[count++] = 'r';
+                val[count++] = 'u';
+                val[count++] = 'e';
+            } else {
+                val[count++] = 'f';
+                val[count++] = 'a';
+                val[count++] = 'l';
+                val[count++] = 's';
+                val[count++] = 'e';
+            }
+        } else {
+            if (b) {
+                checkOffset(count + 4, val.length >> 1);
+                StringUTF16.putChar(val, count++, 't');
+                StringUTF16.putChar(val, count++, 'r');
+                StringUTF16.putChar(val, count++, 'u');
+                StringUTF16.putChar(val, count++, 'e');
+            } else {
+                checkOffset(count + 5, val.length >> 1);
+                StringUTF16.putChar(val, count++, 'f');
+                StringUTF16.putChar(val, count++, 'a');
+                StringUTF16.putChar(val, count++, 'l');
+                StringUTF16.putChar(val, count++, 's');
+                StringUTF16.putChar(val, count++, 'e');
         }
+        }
+        this.count = count;
         return this;
     }
 
     /**
      * Appends the string representation of the {@code char}

@@ -625,11 +706,18 @@
      * @return  a reference to this object.
      */
     @Override
     public AbstractStringBuilder append(char c) {
         ensureCapacityInternal(count + 1);
-        value[count++] = c;
+        if (isLatin1() && StringLatin1.canEncode(c)) {
+            value[count++] = (byte)c;
+        } else {
+            if (isLatin1()) {
+                inflate();
+            }
+            StringUTF16.putCharSB(value, count++, c);
+        }
         return this;
     }
 
     /**
      * Appends the string representation of the {@code int}

@@ -650,11 +738,17 @@
         }
         int appendedLength = (i < 0) ? Integer.stringSize(-i) + 1
                                      : Integer.stringSize(i);
         int spaceNeeded = count + appendedLength;
         ensureCapacityInternal(spaceNeeded);
+        if (isLatin1()) {
         Integer.getChars(i, spaceNeeded, value);
+        } else {
+            byte[] val = this.value;
+            checkOffset(spaceNeeded, val.length >> 1);
+            Integer.getCharsUTF16(i, spaceNeeded, val);
+        }
         count = spaceNeeded;
         return this;
     }
 
     /**

@@ -676,11 +770,17 @@
         }
         int appendedLength = (l < 0) ? Long.stringSize(-l) + 1
                                      : Long.stringSize(l);
         int spaceNeeded = count + appendedLength;
         ensureCapacityInternal(spaceNeeded);
+        if (isLatin1()) {
         Long.getChars(l, spaceNeeded, value);
+        } else {
+            byte[] val = this.value;
+            checkOffset(spaceNeeded, val.length >> 1);
+            Long.getCharsUTF16(l, spaceNeeded, val);
+        }
         count = spaceNeeded;
         return this;
     }
 
     /**

@@ -730,19 +830,17 @@
      * @throws     StringIndexOutOfBoundsException  if {@code start}
      *             is negative, greater than {@code length()}, or
      *             greater than {@code end}.
      */
     public AbstractStringBuilder delete(int start, int end) {
-        if (start < 0)
-            throw new StringIndexOutOfBoundsException(start);
-        if (end > count)
+        if (end > count) {
             end = count;
-        if (start > end)
-            throw new StringIndexOutOfBoundsException();
+        }
+        checkRangeSIOOBE(start, end, count);
         int len = end - start;
         if (len > 0) {
-            System.arraycopy(value, start+len, value, start, count-end);
+            shift(end, -len);
             count -= len;
         }
         return this;
     }
 

@@ -764,24 +862,14 @@
      * @return  a reference to this object.
      * @exception IllegalArgumentException if the specified
      * {@code codePoint} isn't a valid Unicode code point
      */
     public AbstractStringBuilder appendCodePoint(int codePoint) {
-        final int count = this.count;
-
         if (Character.isBmpCodePoint(codePoint)) {
-            ensureCapacityInternal(count + 1);
-            value[count] = (char) codePoint;
-            this.count = count + 1;
-        } else if (Character.isValidCodePoint(codePoint)) {
-            ensureCapacityInternal(count + 2);
-            Character.toSurrogates(codePoint, value, count);
-            this.count = count + 2;
-        } else {
-            throw new IllegalArgumentException();
+            return append((char)codePoint);
         }
-        return this;
+        return append(Character.toChars(codePoint));
     }
 
     /**
      * Removes the {@code char} at the specified position in this
      * sequence. This sequence is shortened by one {@code char}.

@@ -798,13 +886,12 @@
      * @throws      StringIndexOutOfBoundsException  if the {@code index}
      *              is negative or greater than or equal to
      *              {@code length()}.
      */
     public AbstractStringBuilder deleteCharAt(int index) {
-        if ((index < 0) || (index >= count))
-            throw new StringIndexOutOfBoundsException(index);
-        System.arraycopy(value, index+1, value, index, count-index-1);
+        checkIndex(index, count);
+        shift(index + 1, -1);
         count--;
         return this;
     }
 
     /**

@@ -825,26 +912,20 @@
      * @throws     StringIndexOutOfBoundsException  if {@code start}
      *             is negative, greater than {@code length()}, or
      *             greater than {@code end}.
      */
     public AbstractStringBuilder replace(int start, int end, String str) {
-        if (start < 0)
-            throw new StringIndexOutOfBoundsException(start);
-        if (start > count)
-            throw new StringIndexOutOfBoundsException("start > length()");
-        if (start > end)
-            throw new StringIndexOutOfBoundsException("start > end");
-
-        if (end > count)
+        if (end > count) {
             end = count;
+        }
+        checkRangeSIOOBE(start, end, count);
         int len = str.length();
         int newCount = count + len - (end - start);
         ensureCapacityInternal(newCount);
-
-        System.arraycopy(value, end, value, start + len, count - end);
-        str.getChars(value, start);
+        shift(end, newCount - count);
         count = newCount;
+        putStringAt(start, str);
         return this;
     }
 
     /**
      * Returns a new {@code String} that contains a subsequence of

@@ -905,17 +986,20 @@
      *             or {@code end} are negative or greater than
      *             {@code length()}, or {@code start} is
      *             greater than {@code end}.
      */
     public String substring(int start, int end) {
-        if (start < 0)
-            throw new StringIndexOutOfBoundsException(start);
-        if (end > count)
-            throw new StringIndexOutOfBoundsException(end);
-        if (start > end)
-            throw new StringIndexOutOfBoundsException(end - start);
-        return new String(value, start, end - start);
+        checkRangeSIOOBE(start, end, count);
+        if (isLatin1()) {
+            return StringLatin1.newString(value, start, end - start);
+        }
+        return StringUTF16.newStringSB(value, start, end - start);
+    }
+
+    private void shift(int offset, int n) {
+        System.arraycopy(value, offset << coder,
+                         value, (offset + n) << coder, (count - offset) << coder);
     }
 
     /**
      * Inserts the string representation of a subarray of the {@code str}
      * array argument into this sequence. The subarray begins at the

@@ -938,20 +1022,16 @@
      *             {@code str.length}.
      */
     public AbstractStringBuilder insert(int index, char[] str, int offset,
                                         int len)
     {
-        if ((index < 0) || (index > length()))
-            throw new StringIndexOutOfBoundsException(index);
-        if ((offset < 0) || (len < 0) || (offset > str.length - len))
-            throw new StringIndexOutOfBoundsException(
-                "offset " + offset + ", len " + len + ", str.length "
-                + str.length);
+        checkOffset(index, count);
+        checkRangeSIOOBE(offset, offset + len, str.length);
         ensureCapacityInternal(count + len);
-        System.arraycopy(value, index, value, index + len, count - index);
-        System.arraycopy(str, offset, value, index, len);
+        shift(index, len);
         count += len;
+        putCharsAt(index, str, offset, offset + len);
         return this;
     }
 
     /**
      * Inserts the string representation of the {@code Object}

@@ -1006,19 +1086,19 @@
      * @param      str      a string.
      * @return     a reference to this object.
      * @throws     StringIndexOutOfBoundsException  if the offset is invalid.
      */
     public AbstractStringBuilder insert(int offset, String str) {
-        if ((offset < 0) || (offset > length()))
-            throw new StringIndexOutOfBoundsException(offset);
-        if (str == null)
+        checkOffset(offset, count);
+        if (str == null) {
             str = "null";
+        }
         int len = str.length();
         ensureCapacityInternal(count + len);
-        System.arraycopy(value, offset, value, offset + len, count - offset);
-        str.getChars(value, offset);
+        shift(offset, len);
         count += len;
+        putStringAt(offset, str);
         return this;
     }
 
     /**
      * Inserts the string representation of the {@code char} array

@@ -1043,17 +1123,16 @@
      * @param      str      a character array.
      * @return     a reference to this object.
      * @throws     StringIndexOutOfBoundsException  if the offset is invalid.
      */
     public AbstractStringBuilder insert(int offset, char[] str) {
-        if ((offset < 0) || (offset > length()))
-            throw new StringIndexOutOfBoundsException(offset);
+        checkOffset(offset, count);
         int len = str.length;
         ensureCapacityInternal(count + len);
-        System.arraycopy(value, offset, value, offset + len, count - offset);
-        System.arraycopy(str, 0, value, offset, len);
+        shift(offset, len);
         count += len;
+        putCharsAt(offset, str, 0, len);
         return this;
     }
 
     /**
      * Inserts the specified {@code CharSequence} into this sequence.

@@ -1075,14 +1154,16 @@
      * @param      s the sequence to be inserted
      * @return     a reference to this object.
      * @throws     IndexOutOfBoundsException  if the offset is invalid.
      */
     public AbstractStringBuilder insert(int dstOffset, CharSequence s) {
-        if (s == null)
+        if (s == null) {
             s = "null";
-        if (s instanceof String)
+        }
+        if (s instanceof String) {
             return this.insert(dstOffset, (String)s);
+        }
         return this.insert(dstOffset, s, 0, s.length());
     }
 
     /**
      * Inserts a subsequence of the specified {@code CharSequence} into

@@ -1127,26 +1208,22 @@
      *              {@code start} or {@code end} are negative, or
      *              {@code start} is greater than {@code end} or
      *              {@code end} is greater than {@code s.length()}
      */
      public AbstractStringBuilder insert(int dstOffset, CharSequence s,
-                                         int start, int end) {
-        if (s == null)
+                                        int start, int end)
+    {
+        if (s == null) {
             s = "null";
-        if ((dstOffset < 0) || (dstOffset > this.length()))
-            throw new IndexOutOfBoundsException("dstOffset "+dstOffset);
-        if ((start < 0) || (end < 0) || (start > end) || (end > s.length()))
-            throw new IndexOutOfBoundsException(
-                "start " + start + ", end " + end + ", s.length() "
-                + s.length());
+        }
+        checkOffset(dstOffset, count);
+        checkRange(start, end, s.length());
         int len = end - start;
         ensureCapacityInternal(count + len);
-        System.arraycopy(value, dstOffset, value, dstOffset + len,
-                         count - dstOffset);
-        for (int i=start; i<end; i++)
-            value[dstOffset++] = s.charAt(i);
+        shift(dstOffset, len);
         count += len;
+        putCharsAt(dstOffset, s, start, end);
         return this;
     }
 
     /**
      * Inserts the string representation of the {@code boolean}

@@ -1189,14 +1266,22 @@
      * @param      c        a {@code char}.
      * @return     a reference to this object.
      * @throws     IndexOutOfBoundsException  if the offset is invalid.
      */
     public AbstractStringBuilder insert(int offset, char c) {
+        checkOffset(offset, count);
         ensureCapacityInternal(count + 1);
-        System.arraycopy(value, offset, value, offset + 1, count - offset);
-        value[offset] = c;
+        shift(offset, 1);
         count += 1;
+        if (isLatin1() && StringLatin1.canEncode(c)) {
+            value[offset] = (byte)c;
+        } else {
+            if (isLatin1()) {
+                inflate();
+            }
+            StringUTF16.putCharSB(value, offset, c);
+        }
         return this;
     }
 
     /**
      * Inserts the string representation of the second {@code int}

@@ -1324,11 +1409,11 @@
      * @return  the index of the first occurrence of the specified substring,
      *          starting at the specified index,
      *          or {@code -1} if there is no such occurrence.
      */
     public int indexOf(String str, int fromIndex) {
-        return String.indexOf(value, 0, count, str, fromIndex);
+        return String.indexOf(value, coder, count, str, fromIndex);
     }
 
     /**
      * Returns the index within this string of the last occurrence of the
      * specified substring.  The last occurrence of the empty string "" is

@@ -1364,11 +1449,11 @@
      * @return  the index of the last occurrence of the specified substring,
      *          searching backward from the specified index,
      *          or {@code -1} if there is no such occurrence.
      */
     public int lastIndexOf(String str, int fromIndex) {
-        return String.lastIndexOf(value, 0, count, str, fromIndex);
+        return String.lastIndexOf(value, coder, count, str, fromIndex);
     }
 
     /**
      * Causes this character sequence to be replaced by the reverse of
      * the sequence. If there are any surrogate pairs included in the

@@ -1390,38 +1475,51 @@
      * a valid surrogate pair.
      *
      * @return  a reference to this object.
      */
     public AbstractStringBuilder reverse() {
-        boolean hasSurrogates = false;
+        byte[] val = this.value;
+        int count = this.count;
+        int coder = this.coder;
         int n = count - 1;
+        if (COMPACT_STRINGS && coder == LATIN1) {
         for (int j = (n-1) >> 1; j >= 0; j--) {
             int k = n - j;
-            char cj = value[j];
-            char ck = value[k];
-            value[j] = ck;
-            value[k] = cj;
+                byte cj = val[j];
+                val[j] = val[k];
+                val[k] = cj;
+            }
+        } else {
+            checkOffset(count, val.length >> 1);
+            boolean hasSurrogates = false;
+            for (int j = (n-1) >> 1; j >= 0; j--) {
+                int k = n - j;
+                char cj = StringUTF16.getChar(val, j);
+                char ck = StringUTF16.getChar(val, k);
+                StringUTF16.putChar(val, j, ck);
+                StringUTF16.putChar(val, k, cj);
             if (Character.isSurrogate(cj) ||
                 Character.isSurrogate(ck)) {
                 hasSurrogates = true;
             }
         }
         if (hasSurrogates) {
-            reverseAllValidSurrogatePairs();
+                reverseAllValidSurrogatePairs(val, count);
+            }
         }
         return this;
     }
 
     /** Outlined helper method for reverse() */
-    private void reverseAllValidSurrogatePairs() {
+    private void reverseAllValidSurrogatePairs(byte[] val, int count) {
         for (int i = 0; i < count - 1; i++) {
-            char c2 = value[i];
+            char c2 = StringUTF16.getChar(val, i);
             if (Character.isLowSurrogate(c2)) {
-                char c1 = value[i + 1];
+                char c1 = StringUTF16.getChar(val, i + 1);
                 if (Character.isHighSurrogate(c1)) {
-                    value[i++] = c1;
-                    value[i] = c2;
+                    StringUTF16.putChar(val, i++, c1);
+                    StringUTF16.putChar(val, i, c2);
                 }
             }
         }
     }
 

@@ -1442,35 +1540,180 @@
      * {@inheritDoc}
      * @since 1.9
      */
     @Override
     public IntStream chars() {
+        byte[] val = this.value; int count = this.count; byte coder = this.coder;
+        checkOffset(count, val.length >> coder);
         // Reuse String-based spliterator. This requires a supplier to
         // capture the value and count when the terminal operation is executed
         return StreamSupport.intStream(
-                () -> new String.IntCharArraySpliterator(value, 0, count, 0),
+                () -> coder == LATIN1 ? new StringLatin1.CharsSpliterator(val, 0, count, 0)
+                                      : new StringUTF16.CharsSpliterator(val, 0, count, 0),
                 Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED,
                 false);
     }
 
     /**
      * {@inheritDoc}
      * @since 1.9
      */
     @Override
     public IntStream codePoints() {
+        byte[] val = this.value; int count = this.count; byte coder = this.coder;
+        checkOffset(count, val.length >> coder);
         // Reuse String-based spliterator. This requires a supplier to
         // capture the value and count when the terminal operation is executed
         return StreamSupport.intStream(
-                () -> new String.CodePointsSpliterator(value, 0, count, 0),
+                () -> coder == LATIN1 ? new StringLatin1.CharsSpliterator(val, 0, count, 0)
+                                      : new StringUTF16.CodePointsSpliterator(val, 0, count, 0),
                 Spliterator.ORDERED,
                 false);
     }
 
     /**
      * Needed by {@code String} for the contentEquals method.
      */
-    final char[] getValue() {
+    final byte[] getValue() {
         return value;
     }
 
+    /*
+     * Invoker guarantees it is in UTF16 (inflate itself for asb), if two
+     * coders are different and the dstBegin has enough space
+     *
+     * @param dstBegin  the char index, not offset of byte[]
+     * @param coder     the coder of dst[]
+     */
+    protected void getBytes(byte dst[], int dstBegin, byte coder) {
+        if (this.coder == coder) {
+            System.arraycopy(value, 0, dst, dstBegin << coder, count << coder);
+        } else {        // this.coder == LATIN && coder == UTF16
+            StringLatin1.inflateSB(value, dst, dstBegin, count);
+        }
+    }
+
+    /* for readObject() */
+    protected void initBytes(char[] value, int off, int len) {
+        if (String.COMPACT_STRINGS) {
+            this.value = StringUTF16.compress(value, off, len);
+            if (this.value != null) {
+                this.coder = LATIN1;
+                return;
+            }
+        }
+        this.coder = UTF16;
+        this.value = StringUTF16.toBytes(value, off, len);
+    }
+
+    final byte getCoder() {
+        return COMPACT_STRINGS ? coder : UTF16;
+    }
+
+    final boolean isLatin1() {
+        return COMPACT_STRINGS && coder == LATIN1;
+    }
+
+    private final void putCharsAt(int index, char[] s, int off, int end) {
+        if (isLatin1()) {
+            byte[] val = this.value;
+            for (int i = off, j = index; i < end; i++) {
+                char c = s[i];
+                if (StringLatin1.canEncode(c)) {
+                    val[j++] = (byte)c;
+                } else {
+                    inflate();
+                    StringUTF16.putCharsSB(this.value, j, s, i, end);
+                    return;
+                }
+            }
+        } else {
+            StringUTF16.putCharsSB(this.value, index, s, off, end);
+        }
+    }
+
+    private final void putCharsAt(int index, CharSequence s, int off, int end) {
+        if (isLatin1()) {
+            byte[] val = this.value;
+            for (int i = off, j = index; i < end; i++) {
+                char c = s.charAt(i);
+                if (StringLatin1.canEncode(c)) {
+                    val[j++] = (byte)c;
+                } else {
+                    inflate();
+                    StringUTF16.putCharsSB(this.value, j, s, i, end);
+                    return;
+                }
+            }
+        } else {
+            StringUTF16.putCharsSB(this.value, index, s, off, end);
+        }
+    }
+
+    private final void putStringAt(int index, String str) {
+        if (getCoder() != str.coder()) {
+            inflate();
+        }
+        byte[] val = this.value;
+        byte coder = this.coder;
+        checkOffset(index + str.length(), val.length >> coder);
+        str.getBytes(val, index, coder);
+    }
+
+    private final void appendChars(char[] s, int off, int end) {
+        if (isLatin1()) {
+            byte[] val = this.value;
+            for (int i = off, j = count; i < end; i++) {
+                char c = s[i];
+                if (StringLatin1.canEncode(c)) {
+                    val[j++] = (byte)c;
+                } else {
+                    count = j;
+                    inflate();
+                    StringUTF16.putCharsSB(this.value, j, s, i, end);
+                    count += end - i;
+                    return;
+                }
+            }
+        } else {
+            StringUTF16.putCharsSB(this.value, count, s, off, end);
+        }
+        count += end - off;
+    }
+
+    private final void appendChars(CharSequence s, int off, int end) {
+        if (isLatin1()) {
+            byte[] val = this.value;
+            for (int i = off, j = count; i < end; i++) {
+                char c = s.charAt(i);
+                if (StringLatin1.canEncode(c)) {
+                    val[j++] = (byte)c;
+                } else {
+                    count = j;
+                    inflate();
+                    StringUTF16.putCharsSB(this.value, j, s, i, end);
+                    count += end - i;
+                    return;
+                }
+            }
+        } else {
+            StringUTF16.putCharsSB(this.value, count, s, off, end);
+        }
+        count += end - off;
+    }
+
+    /* IndexOutOfBoundsException, if out of bounds */
+    private static void checkRange(int start, int end, int len) {
+        if (start < 0 || start > end || end > len) {
+            throw new IndexOutOfBoundsException(
+                "start " + start + ", end " + end + ", length " + len);
+        }
+    }
+
+    /* StringIndexOutOfBoundsException, if out of bounds */
+    private static void checkRangeSIOOBE(int start, int end, int len) {
+        if (start < 0 || start > end || end > len) {
+            throw new StringIndexOutOfBoundsException(
+                "start " + start + ", end " + end + ", length " + len);
+        }
+    }
 }