/** The value is used for character storage. */private final char value[];

/** Cache the hash code for the string */private int hash; // Default to 0

/** use serialVersionUID from JDK 1.0.2 for interoperability */private static final long serialVersionUID = -6849794470754667710L;

/*** Class String is special cased within the Serialization Stream Protocol.** A String instance is written into an ObjectOutputStream according to* <a href="{@docRoot}/../platform/serialization/spec/output.html">* Object Serialization Specification, Section 6.2, "Stream Elements"</a>*/private static final ObjectStreamField[] serialPersistentFields =new ObjectStreamField[0];

private static final ObjectStreamField[] serialPersistentFields =
{  new ObjectStreamField("name", String.class),   new ObjectStreamField("a", Integer.TYPE)
}; 

public String(byte bytes[]) {this(bytes, 0, bytes.length);}
public String(StringBuffer buffer) {synchronized(buffer) {this.value = Arrays.copyOf(buffer.getValue(), buffer.length());}}
public String(StringBuilder builder) {this.value = Arrays.copyOf(builder.getValue(), builder.length());}

// 返回字符串的长度  public int length() {return value.length;}// 字符串是否为空public boolean isEmpty() {return value.length == 0;}// 字符串目标位置的字符public char charAt(int index) {if ((index < 0) || (index >= value.length)) {throw new StringIndexOutOfBoundsException(index);}return value[index];}// 返回指定索引处的字符public int codePointAt(int index) {if ((index < 0) || (index >= value.length)) {throw new StringIndexOutOfBoundsException(index);}return Character.codePointAtImpl(value, index, value.length);}// 返回指定索引之前的字符public int codePointBefore(int index) {int i = index - 1;if ((i < 0) || (i >= value.length)) {throw new StringIndexOutOfBoundsException(index);}return Character.codePointBeforeImpl(value, index, 0);}// 返回此 String 的指定文本范围中的 Unicode 代码点数public int codePointCount(int beginIndex, int endIndex) {if (beginIndex < 0 || endIndex > value.length || beginIndex > endIndex) {throw new IndexOutOfBoundsException();}return Character.codePointCountImpl(value, beginIndex, endIndex - beginIndex);}
//返回从0处开始的第i个Code Point的位置
public int offsetByCodePoints(int index, int codePointOffset) {if (index < 0 || index > value.length) {throw new IndexOutOfBoundsException();}return Character.offsetByCodePointsImpl(value, 0, value.length,index, codePointOffset);}//判断两个字符串是否相等
public boolean equals(Object anObject) {if (this == anObject) {return true;}if (anObject instanceof String) {String anotherString = (String)anObject;int n = value.length;if (n == anotherString.value.length) {char v1[] = value;char v2[] = anotherString.value;int i = 0;while (n-- != 0) {if (v1[i] != v2[i])return false;i++;}return true;}}return false;}//不区分大小写的情况下比较两个字符串是否相等
public boolean equalsIgnoreCase(String anotherString) {return (this == anotherString) ? true: (anotherString != null)&& (anotherString.value.length == value.length)&& regionMatches(true, 0, anotherString, 0, value.length);}
//计算当前字符串比目标字符串长度大多少
public int compareTo(String anotherString) {int len1 = value.length;int len2 = anotherString.value.length;int lim = Math.min(len1, len2);char v1[] = value;char v2[] = anotherString.value;int k = 0;while (k < lim) {char c1 = v1[k];char c2 = v2[k];if (c1 != c2) {return c1 - c2;}k++;}return len1 - len2;}

//获取哈希值
public int hashCode() {int h = hash;if (h == 0 && value.length > 0) {char val[] = value;for (int i = 0; i < value.length; i++) {h = 31 * h + val[i];}hash = h;}return h;}
//返回某个指定的字符串值在字符串中首次出现的位置
public int indexOf(int ch) {return indexOf(ch, 0);}
public int indexOf(int ch, int fromIndex) {final int max = value.length;if (fromIndex < 0) {fromIndex = 0;} else if (fromIndex >= max) {// Note: fromIndex might be near -1>>>1.return -1;}if (ch < Character.MIN_SUPPLEMENTARY_CODE_POINT) {// handle most cases here (ch is a BMP code point or a// negative value (invalid code point))final char[] value = this.value;for (int i = fromIndex; i < max; i++) {if (value[i] == ch) {return i;}}return -1;} else {return indexOfSupplementary(ch, fromIndex);}}
//返回某个指定的字符串值在字符串中最后一次出现的位置
public int lastIndexOf(int ch) {return lastIndexOf(ch, value.length - 1);}
public int lastIndexOf(int ch, int fromIndex) {if (ch < Character.MIN_SUPPLEMENTARY_CODE_POINT) {// handle most cases here (ch is a BMP code point or a// negative value (invalid code point))final char[] value = this.value;int i = Math.min(fromIndex, value.length - 1);for (; i >= 0; i--) {if (value[i] == ch) {return i;}}return -1;} else {return lastIndexOfSupplementary(ch, fromIndex);}}
//从指定位置截取字符串直至最后一位
public String substring(int beginIndex) {if (beginIndex < 0) {throw new StringIndexOutOfBoundsException(beginIndex);}int subLen = value.length - beginIndex;if (subLen < 0) {throw new StringIndexOutOfBoundsException(subLen);}return (beginIndex == 0) ? this : new String(value, beginIndex, subLen);}
//截取字符串从beginIndex至beginIndex
public String substring(int beginIndex, int endIndex) {if (beginIndex < 0) {throw new StringIndexOutOfBoundsException(beginIndex);}if (endIndex > value.length) {throw new StringIndexOutOfBoundsException(endIndex);}int subLen = endIndex - beginIndex;if (subLen < 0) {throw new StringIndexOutOfBoundsException(subLen);}return ((beginIndex == 0) && (endIndex == value.length)) ? this: new String(value, beginIndex, subLen);}

//字符串拼接
public String concat(String str) {int otherLen = str.length();if (otherLen == 0) {return this;}int len = value.length;char buf[] = Arrays.copyOf(value, len + otherLen);str.getChars(buf, len);return new String(buf, true);}
//字符串替换
public String replace(char oldChar, char newChar) {if (oldChar != newChar) {int len = value.length;int i = -1;char[] val = value; /* avoid getfield opcode */while (++i < len) {if (val[i] == oldChar) {break;}}if (i < len) {char buf[] = new char[len];for (int j = 0; j < i; j++) {buf[j] = val[j];}while (i < len) {char c = val[i];buf[i] = (c == oldChar) ? newChar : c;i++;}return new String(buf, true);}}return this;}
//判断字符串是否包含在另一个字符串中
public boolean contains(CharSequence s) {return indexOf(s.toString()) > -1;}
//将目标字符串中匹配的字符全部替换成另一字符串
public String replaceAll(String regex, String replacement) {return Pattern.compile(regex).matcher(this).replaceAll(replacement);}
//按约定分隔符将目标字符串分割成多个字符串并返回字符串数组
public String[] split(String regex, int limit) {/* fastpath if the regex is a(1)one-char String and this character is not one of theRegEx's meta characters ".$|()[{^?*+\\", or(2)two-char String and the first char is the backslash andthe second is not the ascii digit or ascii letter.*/char ch = 0;if (((regex.value.length == 1 &&".$|()[{^?*+\\".indexOf(ch = regex.charAt(0)) == -1) ||(regex.length() == 2 &&regex.charAt(0) == '\\' &&(((ch = regex.charAt(1))-'0')|('9'-ch)) < 0 &&((ch-'a')|('z'-ch)) < 0 &&((ch-'A')|('Z'-ch)) < 0)) &&(ch < Character.MIN_HIGH_SURROGATE ||ch > Character.MAX_LOW_SURROGATE)){int off = 0;int next = 0;boolean limited = limit > 0;ArrayList<String> list = new ArrayList<>();while ((next = indexOf(ch, off)) != -1) {if (!limited || list.size() < limit - 1) {list.add(substring(off, next));off = next + 1;} else {    // last one//assert (list.size() == limit - 1);
                    list.add(substring(off, value.length));off = value.length;break;}}// If no match was found, return thisif (off == 0)return new String[]{this};// Add remaining segmentif (!limited || list.size() < limit)list.add(substring(off, value.length));// Construct resultint resultSize = list.size();if (limit == 0) {while (resultSize > 0 && list.get(resultSize - 1).length() == 0) {resultSize--;}}String[] result = new String[resultSize];return list.subList(0, resultSize).toArray(result);}return Pattern.compile(regex).split(this, limit);}