1.类声明：
public final class String implements java.io.Serializable, Comparable<String>, CharSequence {}2.变量：
private final char value[];//存储字符串 public static final Comparator<String> CASE_INSENSITIVE_ORDER = new CaseInsensitiveComparator();//静态内部类，比较器3.方法：
public String(char value[]) { this.value = Arrays.copyOf(value, value.length); } //通过String构造String public String(String original) { this.value = original.value; this.hash = original.hash; } //通过int数组构造，考虑每个int是不是一个char，是不是一个Unicode，如果都不是则抛出异常 public String(int[] codePoints, int offset, int count) { if (offset < 0) { throw new StringIndexOutOfBoundsException(offset); } if (count <= 0) { if (count < 0) { throw new StringIndexOutOfBoundsException(count); } if (offset <= codePoints.length) { this.value = "".value; return; } } // Note: offset or count might be near -1>>>1. if (offset > codePoints.length - count) { throw new StringIndexOutOfBoundsException(offset + count); } final int end = offset + count; // Pass 1: Compute precise size of char[] int n = count; for (int i = offset; i < end; i++) { int c = codePoints[i]; if (Character.isBmpCodePoint(c)) continue; else if (Character.isValidCodePoint(c)) n++;//如果不是char,但是是unicode字符，则添加一个字符存储 else throw new IllegalArgumentException(Integer.toString(c)); } // Pass 2: Allocate and fill in char[] final char[] v = new char[n]; for (int i = offset, j = 0; i < end; i++, j++) { int c = codePoints[i]; if (Character.isBmpCodePoint(c)) v[j] = (char)c; else Character.toSurrogates(c, v, j++);//将一个int存储为2个字符 } this.value = v; } //通过字节数组进行构造，调用SringCoding将其解码为字符 public String(byte bytes[], int offset, int length, Charset charset) { if (charset == null) throw new NullPointerException("charset"); checkBounds(bytes, offset, length); this.value = StringCoding.decode(charset, bytes, offset, length); } //通过StringBuffer构造，加入同步，多线程可以同时使用同一个buffer进行构造 public String(StringBuffer buffer) { synchronized(buffer) { this.value = Arrays.copyOf(buffer.getValue(), buffer.length()); } } //通过StringBuilder进行构造 public String(StringBuilder builder) { this.value = Arrays.copyOf(builder.getValue(), builder.length()); } //charAt方法直接返会下标位置的字符 public char charAt(int index) { if ((index < 0) || (index >= value.length)) { throw new StringIndexOutOfBoundsException(index); } return value[index]; } //复制字符串到字符数组指定位置 void getChars(char dst[], int dstBegin) { System.arraycopy(value, 0, dst, dstBegin, value.length); } //将字符串编码为指定字符集的字节数组 public byte[] getBytes(String charsetName) throws UnsupportedEncodingException { if (charsetName == null) throw new NullPointerException(); return StringCoding.encode(charsetName, value, 0, value.length); } //覆写equals方法，同一个对象，或者每个字符都相等，才返回true 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; } //将字符串与CharSequence比较，若是StringBuffer，还需要加锁比较，对StringBuffer对象加锁 public boolean contentEquals(CharSequence cs) { // Argument is a StringBuffer, StringBuilder if (cs instanceof AbstractStringBuilder) { if (cs instanceof StringBuffer) { synchronized(cs) { return nonSyncContentEquals((AbstractStringBuilder)cs); } } else { return nonSyncContentEquals((AbstractStringBuilder)cs); } } // Argument is a String if (cs instanceof String) { return equals(cs); } // Argument is a generic CharSequence char v1[] = value; int n = v1.length; if (n != cs.length()) { return false; } for (int i = 0; i < n; i++) { if (v1[i] != cs.charAt(i)) { return false; } } return true; } //跟另一个String比较 public boolean equalsIgnoreCase(String anotherString) { return (this == anotherString) ? true : (anotherString != null) && (anotherString.value.length == value.length) && regionMatches(true, 0, anotherString, 0, value.length); } //覆盖Comparable接口方法cmpareTo,按字典顺序比较 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; } //通过比较器比较（忽视大小写） public int compareToIgnoreCase(String str) { return CASE_INSENSITIVE_ORDER.compare(this, str); } //在某个下标是否以某个字符串开始 public boolean startsWith(String prefix, int toffset) { char ta[] = value; int to = toffset; char pa[] = prefix.value; int po = 0; int pc = prefix.value.length; // Note: toffset might be near -1>>>1. if ((toffset < 0) || (toffset > value.length - pc)) { return false; } while (--pc >= 0) { if (ta[to++] != pa[po++]) { return false; } } return true; } //转换为在某个位置以什么字符串开始 public boolean endsWith(String suffix) { return startsWith(suffix, value.length - suffix.value.length); } //从fromIndex往前找，找到第一个ch则返回下标 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); } } //如果常量池中已经有了这个字符串，返回它的引用，否则将这个字符串加入常量池同时返回引用 public native String intern(); //正则匹配 public boolean matches(String regex) { return Pattern.matches(regex, this); }