?????? CharSequence、String、StringBuffer、StringBuilder详解：
????? String 继承于CharSequence，也就是说String也是CharSequence类型。除了String实现了CharSequence之 外，StringBuffer和StringBuilder也实现了CharSequence接口。需要说明的是，CharSequence就是字符序 列，String, StringBuilder和StringBuffer本质上都是通过字符数组实现的。
????? 继承关系如下图 ：
? ? ? ? ? ?? 
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? ? ?? CharSequence 是一个接口，它只包括length(), charAt(int index), subSequence(int start, int end),toString()这四个方法。代码如下：
????? CharSequence源码(基于jdk1.7.40)
class="java"> package java.lang;
public interface CharSequence {
int length();
char charAt(int index);
CharSequence subSequence(int start, int end);
public String toString();
}
????? String类源码如下：(基于jdk1.7.40)
public String() public String(String original) public String(char[] value) public String(char[] value, int offset, int count) public String(byte[] bytes) public String(byte[] bytes, int offset, int length) public String(byte[] ascii, int hibyte) public String(byte[] ascii, int hibyte, int offset, int count) public String(byte[] bytes, String charsetName) public String(byte[] bytes, int offset, int length, String charsetName) public String(byte[] bytes, Charset charset) public String(byte[] bytes, int offset, int length, Charset charset) public String(int[] codePoints, int offset, int count) public String(StringBuffer buffer) public String(StringBuilder builder) public char charAt(int index) public int codePointAt(int index) public int codePointBefore(int index) public int codePointCount(int beginIndex, int endIndex) public int compareTo(String anotherString) public int compareToIgnoreCase(String str) public String concat(String str) public boolean contains(CharSequence s) public boolean contentEquals(StringBuffer sb) public boolean contentEquals(CharSequence cs) public static String copyValueOf(char[] data, int offset, int count) public static String copyValueOf(char[] data) public boolean endsWith(String suffix) public boolean equals(Object anObject) public boolean equalsIgnoreCase(String anotherString) public static String format(String format, Object[] args) public static String format(Locale l, String format, Object[] args) public int hashCode() public int indexOf(int ch) public int indexOf(int ch, int fromIndex) public int indexOf(String str) public int indexOf(String str, int fromIndex) public String intern() public int lastIndexOf(int ch) public int lastIndexOf(int ch, int fromIndex) public int lastIndexOf(String str) public int lastIndexOf(String str, int fromIndex) public int length() public boolean matches(String regex) public int offsetByCodePoints(int index, int codePointOffset) public boolean regionMatches(int toffset, String other, int ooffset, int len) public boolean regionMatches(boolean ignoreCase, int toffset, String other, int ooffset, int len) public String replace(char oldChar, char newChar) public String replace(CharSequence target, CharSequence replacement) public String replaceAll(String regex, String replacement) public String replaceFirst(String regex, String replacement) public String[] split(String regex, int limit) public String[] split(String regex) public boolean startsWith(String prefix, int toffset) public boolean startsWith(String prefix) public CharSequence subSequence(int beginIndex, int endIndex) public String substring(int beginIndex) public String substring(int beginIndex, int endIndex) public char[] toCharArray() public String toLowerCase(Locale locale) public String toLowerCase() public String toString() public String toUpperCase(Locale locale) public String toUpperCase() public String trim() public static String valueOf(Object obj) public static String valueOf(char[] data) public static String valueOf(char[] data, int offset, int count) public static String valueOf(boolean b) public static String valueOf(char c) public static String valueOf(int i) public static String valueOf(long l) public static String valueOf(float f) public static String valueOf(double d) public void getBytes(int srcBegin, int srcEnd, byte[] dst, int dstBegin) public byte[] getBytes(String charsetName) public byte[] getBytes(Charset charset) public byte[] getBytes() public void getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin) public boolean isEmpty()
StringBuilder类源码如下：(基于jdk1.7.40)?
StringBuilder() StringBuilder(int capacity) StringBuilder(CharSequence seq) StringBuilder(String str) StringBuilder append(float f) StringBuilder append(double d) StringBuilder append(boolean b) StringBuilder append(int i) StringBuilder append(long l) StringBuilder append(char c) StringBuilder append(char[] chars) StringBuilder append(char[] str, int offset, int len) StringBuilder append(String str) StringBuilder append(Object obj) StringBuilder append(StringBuffer sb) StringBuilder append(CharSequence csq) StringBuilder append(CharSequence csq, int start, int end) StringBuilder appendCodePoint(int codePoint) int capacity() char charAt(int index) int codePointAt(int index) int codePointBefore(int index) int codePointCount(int start, int end) StringBuilder delete(int start, int end) StringBuilder deleteCharAt(int index) void ensureCapacity(int min) void getChars(int start, int end, char[] dst, int dstStart) int indexOf(String subString, int start) int indexOf(String string) StringBuilder insert(int offset, boolean b) StringBuilder insert(int offset, int i) StringBuilder insert(int offset, long l) StringBuilder insert(int offset, float f) StringBuilder insert(int offset, double d) StringBuilder insert(int offset, char c) StringBuilder insert(int offset, char[] ch) StringBuilder insert(int offset, char[] str, int strOffset, int strLen) StringBuilder insert(int offset, String str) StringBuilder insert(int offset, Object obj) StringBuilder insert(int offset, CharSequence s) StringBuilder insert(int offset, CharSequence s, int start, int end) int lastIndexOf(String string) int lastIndexOf(String subString, int start) int length() int offsetByCodePoints(int index, int codePointOffset) StringBuilder replace(int start, int end, String string) StringBuilder reverse() void setCharAt(int index, char ch) void setLength(int length) CharSequence subSequence(int start, int end) String substring(int start) String substring(int start, int end) String toString() void trimToSize()
?StringBuffer类源码如下：(基于jdk1.7.40)
StringBuffer() StringBuffer(int capacity) StringBuffer(String string) StringBuffer(CharSequence cs) StringBuffer append(boolean b) StringBuffer append(int i) StringBuffer append(long l) StringBuffer append(float f) StringBuffer append(double d) synchronized StringBuffer append(char ch) synchronized StringBuffer append(char[] chars) synchronized StringBuffer append(char[] chars, int start, int length) synchronized StringBuffer append(Object obj) synchronized StringBuffer append(String string) synchronized StringBuffer append(StringBuffer sb) synchronized StringBuffer append(CharSequence s) synchronized StringBuffer append(CharSequence s, int start, int end) StringBuffer appendCodePoint(int codePoint) int capacity() synchronized char charAt(int index) synchronized int codePointAt(int index) synchronized int codePointBefore(int index) synchronized int codePointCount(int beginIndex, int endIndex) synchronized StringBuffer delete(int start, int end) synchronized StringBuffer deleteCharAt(int location) synchronized void ensureCapacity(int min) synchronized void getChars(int start, int end, char[] buffer, int idx) synchronized int indexOf(String subString, int start) int indexOf(String string) StringBuffer insert(int index, boolean b) StringBuffer insert(int index, int i) StringBuffer insert(int index, long l) StringBuffer insert(int index, float f) StringBuffer insert(int index, double d) synchronized StringBuffer insert(int index, char ch) synchronized StringBuffer insert(int index, char[] chars) synchronized StringBuffer insert(int index, char[] chars, int start, int length) synchronized StringBuffer insert(int index, String string) StringBuffer insert(int index, Object obj) synchronized StringBuffer insert(int index, CharSequence s) synchronized StringBuffer insert(int index, CharSequence s, int start, int end) int lastIndexOf(String string) synchronized int lastIndexOf(String subString, int start) int length() synchronized int offsetByCodePoints(int index, int codePointOffset) synchronized StringBuffer replace(int start, int end, String string) synchronized StringBuffer reverse() synchronized void setCharAt(int index, char ch) synchronized void setLength(int length) synchronized CharSequence subSequence(int start, int end) synchronized String substring(int start) synchronized String substring(int start, int end) synchronized String toString() synchronized void trimToSize()
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