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Java String之String和CharSequence、StringBuilder和StringBuffer的区别(4)

2. String 构造函数

下面经由过程示例,演示String的各类构造函数的应用措施!

源码如下(StringContructorTest.java):

/**

* String 构造函数演示法度榜样*

* @author skywang*/

import java.nio.charset.Charset;import java.io.UnsupportedEncodingException;

public class StringContructorTest {

public static void main(String[] args) {

testStringConstructors() ;}

/**

* String 构造函数测试法度榜样*/

private static void testStringConstructors() {try {

System.out.println("-------------------------------- testStringConstructors -----------------------");

String str01 = new String();String str02 = new String("String02");

String str03 = new String(new char[]{'s','t','r','0','3'});String str04 = new String(new char[]{'s','t','r','0','4'}, 1, 3);// 1表示肇端位置,3表示个数

String str05 = new String(new byte[]{0x61, 0x62, 0x63, 0x64, 0x65});// 0x61在ASC表中,对应字符"a"; 1表示肇端位置,3表示长度String str06 = new String(new byte[]{0x61, 0x62, 0x63, 0x64, 0x65}, 1, 3); // 0x61在ASC表中,对应字符"a"; 1表示肇端位置,3表示长度

String str07 = new String(new byte[]{0x61, 0x62, 0x63, 0x64, 0x65}, 0);// 0x61在ASC表中,对应字符"a";0,表示“高字节”String str08 = new String(new byte[]{0x61, 0x62, 0x63, 0x64, 0x65}, 0, 1, 3); // 0x61在ASC表中,对应字符"a"; 0,表示“高字节”;1表示肇端位置,3表示长度

String str09 = new String(new byte[]{(byte)0xe5, (byte)0xad, (byte)0x97, /* 字-对应的utf-8编码 */(byte)0xe7, (byte)0xac, (byte)0xa6, /* 符-对应的utf-8编码 */

(byte)0xe7, (byte)0xbc, (byte)0x96, /* 编-对应的utf-8编码 */(byte)0xe7, (byte)0xa0, (byte)0x81, /* 码-对应的utf-8编码 */ },

0, 12, "utf-8");// 0表示肇端位置,12表示长度。String str10 = new String(new byte[]{(byte)0x5b, (byte)0x57, /* 字-对应的utf-16编码 */

(byte)0x7b, (byte)0x26, /* 符-对应的utf-16编码 */(byte)0x7f, (byte)0x16, /* 编-对应的utf-16编码 */

(byte)0x78, (byte)0x01, /* 码-对应的utf-16编码 */ },0, 8, "utf-16");// 0表示肇端位置,8表示长度。

String str11 = new String(new byte[]{(byte)0xd7, (byte)0xd6, /* 字-对应的gb2312编码*/(byte)0xb7, (byte)0xfb, /* 符-对应的gb2312编码 */

(byte)0xb1, (byte)0xe0, /* 编-对应的gb2312编码 */(byte)0xc2, (byte)0xeb, /* 码-对应的gb2312编码 */ },

Charset.forName("gb2312"));String str12 = new String(new byte[]{(byte)0xd7, (byte)0xd6, /* 字-对应的gbk编码 */

(byte)0xb7, (byte)0xfb, /* 符-对应的gbk编码 */(byte)0xb1, (byte)0xe0, /* 编-对应的gbk编码 */

(byte)0xc2, (byte)0xeb, /* 码-对应的gbk编码 */ },0, 8, Charset.forName("gbk"));

String str13 = new String(new int[] {0x5b57, 0x7b26, 0x7f16, 0x7801}, 0, 4);// "字符编码"(\u5b57是‘字’的unicode编码)。0表示肇端位置,4表示长度。String str14 = new String(new StringBuffer("StringBuffer"));

String str15 = new String(new StringBuilder("StringBuilder"));

System.out.printf(" str01=%s \n str02=%s \n str03=%s \n str04=%s \n str05=%s \n str06=%s \n str07=%s \n str08=%s\n str09=%s\n str10=%s\n str11=%s\n str12=%s\n str13=%s\n str14=%s\n str15=%s\n",str01, str02, str03, str04, str05, str06, str07, str08, str09, str10, str11, str12, str13, str14, str15);

System.out.println();} catch (UnsupportedEncodingException e) {

e.printStackTrace();}

}}

运行结果:

-------------------------------- testStringConstructors -----------------------

str01=str02=String02

str03=str03str04=tr0

str05=abcdestr06=bcd

str07=abcdestr08=bcd

str09=字符编码str10=字符编码

str11=字符编码str12=字符编码

str13=字符编码str14=StringBuffer

str15=StringBuilder

演示法度榜样

1. CharSequence

下面经由过程示例,演示CharSequence的应用措施!

源码如下(CharSequenceTest.java):

/**

* CharSequence 演示法度榜样*

* @author skywang*/

import java.nio.charset.Charset;import java.io.UnsupportedEncodingException;

public class CharSequenceTest {

public static void main(String[] args) {

testCharSequence();}

/**

* CharSequence 测试法度榜样*/

private static void testCharSequence() {System.out.println("-------------------------------- testCharSequence -----------------------------");

// 1. CharSequence的子类String

String str = "abcdefghijklmnopqrstuvwxyz";System.out.println("1. String");

System.out.printf("%-30s=%d\n", "str.length()", str.length());System.out.printf("%-30s=%c\n", "str.charAt(5)", str.charAt(5));

String substr = (String)str.subSequence(0,5);System.out.printf("%-30s=%s\n", "str.subSequence(0,5)", substr.toString());

// 2. CharSequence的子类StringBuilder

StringBuilder strbuilder = new StringBuilder("abcdefghijklmnopqrstuvwxyz");System.out.println("2. StringBuilder");

System.out.printf("%-30s=%d\n", "strbuilder.length()", strbuilder.length());System.out.printf("%-30s=%c\n", "strbuilder.charAt(5)", strbuilder.charAt(5));

// 留意:StringBuilder的subSequence()返回的是,实际上是一个String工具!String substrbuilder = (String)strbuilder.subSequence(0,5);

System.out.printf("%-30s=%s\n", "strbuilder.subSequence(0,5)", substrbuilder.toString());

// 3. CharSequence的子类StringBufferStringBuffer strbuffer = new StringBuffer("abcdefghijklmnopqrstuvwxyz");

System.out.println("3. StringBuffer");System.out.printf("%-30s=%d\n", "strbuffer.length()", strbuffer.length());

System.out.printf("%-30s=%c\n", "strbuffer.charAt(5)", strbuffer.charAt(5));// 留意:StringBuffer的subSequence()返回的是,实际上是一个String工具!

String substrbuffer = (String)strbuffer.subSequence(0,5);System.out.printf("%-30s=%s\n", "strbuffer.subSequence(0,5)", substrbuffer.toString());

System.out.println();

}}

运行结果

-------------------------------- testCharSequence -----------------------------

1. Stringstr.length()=26

str.charAt(5)=fstr.subSequence(0,5)=abcde

2. StringBuilderstrbuilder.length()=26

strbuilder.charAt(5)=fstrbuilder.subSequence(0,5)=abcde

3. StringBufferstrbuffer.length()=26

strbuffer.charAt(5)=fstrbuffer.subSequence(0,5)=abcde

CharSequence和String源码

1. CharSequence源码(基于jdk1.7.40)

package java.lang;

public interface CharSequence {

int length();

char charAt(int index);

CharSequence subSequence(int start, int end);

public String toString();

}

2. String.java源码(基于jdk1.7.40)

package java.lang;

import java.io.ObjectStreamField;

import java.io.UnsupportedEncodingException;import java.nio.charset.Charset;

import java.util.ArrayList;import java.util.Arrays;

import java.util.Comparator;import java.util.Formatter;

import java.util.Locale;import java.util.regex.Matcher;

import java.util.regex.Pattern;import java.util.regex.PatternSyntaxException;

public final class String

implements java.io.Serializable, Comparable, CharSequence {private final char value[];

private int hash;

private static final long serialVersionUID = -6849794470754667710L;

private static final ObjectStreamField[] serialPersistentFields =

new ObjectStreamField[0];

public String() {this.value = new char[0];

}

public String(String original) {this.value = original.value;

this.hash = original.hash;}

public String(char value[]) {

this.value = Arrays.copyOf(value, value.length);}

public String(char value[], int offset, int count) {

if (offset 0) {throw new StringIndexOutOfBoundsException(offset);

}if (count 0) {

throw new StringIndexOutOfBoundsException(count);}

// Note: offset or count might be near -1>>>1.if (offset > value.length - count) {

throw new StringIndexOutOfBoundsException(offset + count);}

this.value = Arrays.copyOfRange(value, offset, offset+count);}

public String(int[] codePoints, int offset, int count) {

if (offset 0) {throw new StringIndexOutOfBoundsException(offset);

}if (count 0) {

throw new StringIndexOutOfBoundsException(count);}

// 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

int c = codePoints[i];if (Character.isBmpCodePoint(c))

continue;else if (Character.isValidCodePoint(c))

n++;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

int c = codePoints[i];if (Character.isBmpCodePoint(c))

v[j] = (char)c;else

Character.toSurrogates(c, v, j++);}

this.value = v;

}

@Deprecatedpublic String(byte ascii[], int hibyte, int offset, int count) {

checkBounds(ascii, offset, count);char value[] = new char[count];

if (hibyte == 0) {

for (int i = count; i-- > 0;) {value[i] = (char)(ascii[i + offset] & 0xff);

}} else {

hibyte 8;for (int i = count; i-- > 0;) {

value[i] = (char)(hibyte | (ascii[i + offset] & 0xff));}

}this.value = value;

}

@Deprecatedpublic String(byte ascii[], int hibyte) {

this(ascii, hibyte, 0, ascii.length);}

private static void checkBounds(byte[] bytes, int offset, int length) {

if (length 0)throw new StringIndexOutOfBoundsException(length);

if (offset 0)throw new StringIndexOutOfBoundsException(offset);

if (offset > bytes.length - length)throw new StringIndexOutOfBoundsException(offset + length);

}

public String(byte bytes[], int offset, int length, String charsetName)throws UnsupportedEncodingException {

if (charsetName == null)throw new NullPointerException("charsetName");

checkBounds(bytes, offset, length);this.value = StringCoding.decode(charsetName, bytes, offset, length);

}

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);}

public String(byte bytes[], String charsetName)

throws UnsupportedEncodingException {this(bytes, 0, bytes.length, charsetName);

}

public String(byte bytes[], Charset charset) {this(bytes, 0, bytes.length, charset);

}

public String(byte bytes[], int offset, int length) {checkBounds(bytes, offset, length);

this.value = StringCoding.decode(bytes, offset, length);}

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());}

String(char[] value, boolean share) {

// assert share : "unshared not supported";this.value = value;

}

@DeprecatedString(int offset, int count, char[] value) {

this(value, offset, count);}

public int length() {

return value.length;}

public boolean isEmpty() {

return value.length == 0;}

public char charAt(int index) {

if ((index 0) || (index >= value.length)) {throw new StringIndexOutOfBoundsException(index);

}return value[index];

}

public int codePointAt(int index) {if ((index 0) || (index >= value.length)) {

throw new StringIndexOutOfBoundsException(index);}

return Character.codePointAtImpl(value, index, value.length);}

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);}

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);

}

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);

}

void getChars(char dst[], int dstBegin) {System.arraycopy(value, 0, dst, dstBegin, value.length);

}

public void getChars(int srcBegin, int srcEnd, char dst[], int dstBegin) {if (srcBegin 0) {

throw new StringIndexOutOfBoundsException(srcBegin);}

if (srcEnd > value.length) {throw new StringIndexOutOfBoundsException(srcEnd);

}if (srcBegin > srcEnd) {

throw new StringIndexOutOfBoundsException(srcEnd - srcBegin);}

System.arraycopy(value, srcBegin, dst, dstBegin, srcEnd - srcBegin);}

@Deprecated

public void getBytes(int srcBegin, int srcEnd, byte dst[], int dstBegin) {if (srcBegin 0) {

throw new StringIndexOutOfBoundsException(srcBegin);}

if (srcEnd > value.length) {throw new StringIndexOutOfBoundsException(srcEnd);

}if (srcBegin > srcEnd) {

throw new StringIndexOutOfBoundsException(srcEnd - srcBegin);}

int j = dstBegin;int n = srcEnd;

int i = srcBegin;char[] val = value;/* avoid getfield opcode */

while (i

dst[j++] = (byte)val[i++];}

}

public byte[] getBytes(String charsetName)throws UnsupportedEncodingException {

if (charsetName == null) throw new NullPointerException();return StringCoding.encode(charsetName, value, 0, value.length);

}

public byte[] getBytes(Charset charset) {if (charset == null) throw new NullPointerException();

return StringCoding.encode(charset, value, 0, value.length);}

public byte[] getBytes() {

return StringCoding.encode(value, 0, value.length);}

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;}

public boolean contentEquals(StringBuffer sb) {

synchronized (sb) {return contentEquals((CharSequence) sb);

}}

public boolean contentEquals(CharSequence cs) {

if (value.length != cs.length())return false;

// Argument is a StringBuffer, StringBuilderif (cs instanceof AbstractStringBuilder) {

char v1[] = value;char v2[] = ((AbstractStringBuilder) cs).getValue();

int i = 0;int n = value.length;

while (n-- != 0) {if (v1[i] != v2[i])

return false;i++;

}return true;

}// Argument is a String

if (cs.equals(this))return true;

// Argument is a generic CharSequencechar v1[] = value;

int i = 0;int n = value.length;

while (n-- != 0) {if (v1[i] != cs.charAt(i))

return false;i++;

}return true;

}

public boolean equalsIgnoreCase(String anotherString) {return (this == anotherString) ? true

: (anotherString != null)&& (anotherString.value.length == value.length)

&& regionMatches(true, 0, anotherString, 0, value.length);}

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

char c1 = v1[k];char c2 = v2[k];

if (c1 != c2) {return c1 - c2;

}k++;

}return len1 - len2;

}

public static final Comparator CASE_INSENSITIVE_ORDER= new CaseInsensitiveComparator();

private static class CaseInsensitiveComparatorimplements Comparator, java.io.Serializable {

// use serialVersionUID from JDK 1.2.2 for interoperabilityprivate static final long serialVersionUID = 8575799808933029326L;

public int compare(String s1, String s2) {

int n1 = s1.length();int n2 = s2.length();

int min = Math.min(n1, n2);for (int i = 0; i

char c1 = s1.charAt(i);char c2 = s2.charAt(i);

if (c1 != c2) {c1 = Character.toUpperCase(c1);

c2 = Character.toUpperCase(c2);if (c1 != c2) {

c1 = Character.toLowerCase(c1);c2 = Character.toLowerCase(c2);

if (c1 != c2) {// No overflow because of numeric promotion

return c1 - c2;}

}}

}return n1 - n2;

}}

public int compareToIgnoreCase(String str) {

return CASE_INSENSITIVE_ORDER.compare(this, str);}

public boolean regionMatches(int toffset, String other, int ooffset,

int len) {char ta[] = value;

int to = toffset;char pa[] = other.value;

int po = ooffset;// Note: toffset, ooffset, or len might be near -1>>>1.

if ((ooffset 0) || (toffset 0)|| (toffset > (long)value.length - len)

|| (ooffset > (long)other.value.length - len)) {return false;

}while (len-- > 0) {

if (ta[to++] != pa[po++]) {return false;

}}

return true;}

public boolean regionMatches(boolean ignoreCase, int toffset,

String other, int ooffset, int len) {char ta[] = value;

int to = toffset;char pa[] = other.value;

int po = ooffset;// Note: toffset, ooffset, or len might be near -1>>>1.

if ((ooffset 0) || (toffset 0)|| (toffset > (long)value.length - len)

|| (ooffset > (long)other.value.length - len)) {return false;

}while (len-- > 0) {

char c1 = ta[to++];char c2 = pa[po++];

if (c1 == c2) {continue;

}if (ignoreCase) {

// If characters don't match but case may be ignored,// try converting both characters to uppercase.

// If the results match, then the comparison scan should// continue.

char u1 = Character.toUpperCase(c1);char u2 = Character.toUpperCase(c2);

if (u1 == u2) {continue;

}// Unfortunately, conversion to uppercase does not work properly

// for the Georgian alphabet, which has strange rules about case// conversion.So we need to make one last check before

// exiting.if (Character.toLowerCase(u1) == Character.toLowerCase(u2)) {

continue;}

}return false;

}return true;

}

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;

}

public boolean startsWith(String prefix) {return startsWith(prefix, 0);

}

public boolean endsWith(String suffix) {return startsWith(suffix, value.length - suffix.value.length);

}

public int hashCode() {int h = hash;

if (h == 0 && value.length > 0) {char val[] = value;

for (int i = 0; i

h = 31 * h + val[i];}

hash = h;}

return h;}

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// 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; iif (value[i] == ch) {

return i;}

}return -1;

} else {return indexOfSupplementary(ch, fromIndex);

}}

private int indexOfSupplementary(int ch, int fromIndex) {

if (Character.isValidCodePoint(ch)) {final char[] value = this.value;

final char hi = Character.highSurrogate(ch);final char lo = Character.lowSurrogate(ch);

final int max = value.length - 1;for (int i = fromIndex; i

if (value[i] == hi && value[i + 1] == lo) {return i;

}}

}return -1;

}

public int lastIndexOf(int ch) {return lastIndexOf(ch, value.length - 1);

}

public int lastIndexOf(int ch, int fromIndex) {if (ch

// 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);

}}

private int lastIndexOfSupplementary(int ch, int fromIndex) {

if (Character.isValidCodePoint(ch)) {final char[] value = this.value;

char hi = Character.highSurrogate(ch);char lo = Character.lowSurrogate(ch);

int i = Math.min(fromIndex, value.length - 2);for (; i >= 0; i--) {

if (value[i] == hi && value[i + 1] == lo) {return i;

}}

}return -1;

}

public int indexOf(String str) {return indexOf(str, 0);

}

public int indexOf(String str, int fromIndex) {return indexOf(value, 0, value.length,

str.value, 0, str.value.length, fromIndex);}

static int indexOf(char[] source, int sourceOffset, int sourceCount,

char[] target, int targetOffset, int targetCount,int fromIndex) {

if (fromIndex >= sourceCount) {return (targetCount == 0 ? sourceCount : -1);

}if (fromIndex 0) {

fromIndex = 0;}

if (targetCount == 0) {return fromIndex;

}

char first = target[targetOffset];int max = sourceOffset + (sourceCount - targetCount);

for (int i = sourceOffset + fromIndex; i

/* Look for first character. */if (source[i] != first) {

while (++i}

/* Found first character, now look at the rest of v2 */

if (iint j = i + 1;

int end = j + targetCount - 1;for (int k = targetOffset + 1; j

== target[k]; j++, k++);

if (j == end) {/* Found whole string. */

return i - sourceOffset;}

}}

return -1;}

public int lastIndexOf(String str) {

return lastIndexOf(str, value.length);}

public int lastIndexOf(String str, int fromIndex) {

return lastIndexOf(value, 0, value.length,str.value, 0, str.value.length, fromIndex);

}

static int lastIndexOf(char[] source, int sourceOffset, int sourceCount,char[] target, int targetOffset, int targetCount,

int fromIndex) {/*

* Check arguments; return immediately where possible. For* consistency, don't check for null str.

*/int rightIndex = sourceCount - targetCount;

if (fromIndex 0) {return -1;

}if (fromIndex > rightIndex) {

fromIndex = rightIndex;}

/* Empty string always matches. */if (targetCount == 0) {

return fromIndex;}

int strLastIndex = targetOffset + targetCount - 1;

char strLastChar = target[strLastIndex];int min = sourceOffset + targetCount - 1;

int i = min + fromIndex;

startSearchForLastChar:while (true) {

while (i >= min && source[i] != strLastChar) {i--;

}if (i

return -1;}

int j = i - 1;int start = j - (targetCount - 1);

int k = strLastIndex - 1;

while (j > start) {if (source[j--] != target[k--]) {

i--;continue startSearchForLastChar;

}}

return start - sourceOffset + 1;}

}

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);}

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);

}

public CharSequence subSequence(int beginIndex, int endIndex) {return this.substring(beginIndex, endIndex);

}

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);}

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

if (val[i] == oldChar) {break;

}}

if (ichar buf[] = new char[len];

for (int j = 0; jbuf[j] = val[j];

}while (i

char c = val[i];buf[i] = (c == oldChar) ? newChar : c;

i++;}

return new String(buf, true);}

}return this;

}

public boolean matches(String regex) {return Pattern.matches(regex, this);

}

public boolean contains(CharSequence s) {return indexOf(s.toString()) > -1;

}

public String replaceFirst(String regex, String replacement) {return Pattern.compile(regex).matcher(this).replaceFirst(replacement);

}

public String replaceAll(String regex, String replacement) {return Pattern.compile(regex).matcher(this).replaceAll(replacement);

}

public String replace(CharSequence target, CharSequence replacement) {return Pattern.compile(target.toString(), Pattern.LITERAL).matcher(

this).replaceAll(Matcher.quoteWordStrment(replacement.toString()));}

public String[] split(String regex, int limit) {

/* fastpath if the regex is a(1)one-char String and this character is not one of the

RegEx's meta characters ".$|()[{^?*+\\", or(2)two-char String and the first char is the backslash and

the 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)) &&

(chch > Character.MAX_LOW_SURROGATE))

{int off = 0;

int next = 0;boolean limited = limit > 0;

ArrayList list = new ArrayListwhile ((next = indexOf(ch, off)) != -1) {

if (!limited || list.size() 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()

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);}

public String[] split(String regex) {

return split(regex, 0);}

public String toLowerCase(Locale locale) {

if (locale == null) {throw new NullPointerException();

}

int firstUpper;final int len = value.length;

/* Now check if there are any characters that need to be changed. */

scan: {for (firstUpper = 0 ; firstUpper

char c = value[firstUpper];if ((c >= Character.MIN_HIGH_SURROGATE)

&& (cint supplChar = codePointAt(firstUpper);

if (supplChar != Character.toLowerCase(supplChar)) {break scan;

}firstUpper += Character.charCount(supplChar);

} else {if (c != Character.toLowerCase(c)) {

break scan;}

firstUpper++;}

}return this;

}

char[] result = new char[len];int resultOffset = 0;/* result may grow, so i+resultOffset

* is the write location in result */

/* Just copy the first few lowerCase characters. */System.arraycopy(value, 0, result, 0, firstUpper);

String lang = locale.getLanguage();

boolean localeDependent =(lang == "tr" || lang == "az" || lang == "lt");

char[] lowerCharArray;int lowerChar;

int srcChar;int srcCount;

for (int i = firstUpper; isrcChar = (int)value[i];

if ((char)srcChar >= Character.MIN_HIGH_SURROGATE&& (char)srcChar

srcChar = codePointAt(i);srcCount = Character.charCount(srcChar);

} else {srcCount = 1;

}if (localeDependent || srcChar == '\u03A3') { // GREEK CAPITAL LETTER SIGMA

lowerChar = ConditionalSpecialCasing.toLowerCaseEx(this, i, locale);} else if (srcChar == '\u0130') { // LATIN CAPITAL LETTER I DOT

lowerChar = Character.ERROR;} else {

lowerChar = Character.toLowerCase(srcChar);}

if ((lowerChar == Character.ERROR)|| (lowerChar >= Character.MIN_SUPPLEMENTARY_CODE_POINT)) {

if (lowerChar == Character.ERROR) {if (!localeDependent && srcChar == '\u0130') {

lowerCharArray =ConditionalSpecialCasing.toLowerCaseCharArray(this, i, Locale.ENGLISH);

} else {lowerCharArray =

ConditionalSpecialCasing.toLowerCaseCharArray(this, i, locale);}

} else if (srcCount == 2) {resultOffset += Character.toChars(lowerChar, result, i + resultOffset) - srcCount;

continue;} else {

lowerCharArray = Character.toChars(lowerChar);}

/* Grow result if needed */

int mapLen = lowerCharArray.length;if (mapLen > srcCount) {

char[] result2 = new char[result.length + mapLen - srcCount];System.arraycopy(result, 0, result2, 0, i + resultOffset);

result = result2;}

for (int x = 0; xresult[i + resultOffset + x] = lowerCharArray[x];

}resultOffset += (mapLen - srcCount);

} else {result[i + resultOffset] = (char)lowerChar;

}}

return new String(result, 0, len + resultOffset);}

public String toLowerCase() {

return toLowerCase(Locale.getDefault());}

public String toUpperCase(Locale locale) {

if (locale == null) {throw new NullPointerException();

}

int firstLower;final int len = value.length;

/* Now check if there are any characters that need to be changed. */

scan: {for (firstLower = 0 ; firstLower

int c = (int)value[firstLower];int srcCount;

if ((c >= Character.MIN_HIGH_SURROGATE)&& (c

c = codePointAt(firstLower);srcCount = Character.charCount(c);

} else {srcCount = 1;

}int upperCaseChar = Character.toUpperCaseEx(c);

if ((upperCaseChar == Character.ERROR)|| (c != upperCaseChar)) {

break scan;}

firstLower += srcCount;}

return this;}

char[] result = new char[len]; /* may grow */

int resultOffset = 0;/* result may grow, so i+resultOffset* is the write location in result */

/* Just copy the first few upperCase characters. */

System.arraycopy(value, 0, result, 0, firstLower);

String lang = locale.getLanguage();boolean localeDependent =

(lang == "tr" || lang == "az" || lang == "lt");char[] upperCharArray;

int upperChar;int srcChar;

int srcCount;for (int i = firstLower; i

srcChar = (int)value[i];if ((char)srcChar >= Character.MIN_HIGH_SURROGATE &&

(char)srcCharsrcChar = codePointAt(i);

srcCount = Character.charCount(srcChar);} else {

srcCount = 1;}

if (localeDependent) {upperChar = ConditionalSpecialCasing.toUpperCaseEx(this, i, locale);

} else {upperChar = Character.toUpperCaseEx(srcChar);

}if ((upperChar == Character.ERROR)

|| (upperChar >= Character.MIN_SUPPLEMENTARY_CODE_POINT)) {if (upperChar == Character.ERROR) {

if (localeDependent) {upperCharArray =

ConditionalSpecialCasing.toUpperCaseCharArray(this, i, locale);} else {

upperCharArray = Character.toUpperCaseCharArray(srcChar);}

} else if (srcCount == 2) {resultOffset += Character.toChars(upperChar, result, i + resultOffset) - srcCount;

continue;} else {

upperCharArray = Character.toChars(upperChar);}

/* Grow result if needed */

int mapLen = upperCharArray.length;if (mapLen > srcCount) {

char[] result2 = new char[result.length + mapLen - srcCount];System.arraycopy(result, 0, result2, 0, i + resultOffset);

result = result2;}

for (int x = 0; xresult[i + resultOffset + x] = upperCharArray[x];

}resultOffset += (mapLen - srcCount);

} else {result[i + resultOffset] = (char)upperChar;

}}

return new String(result, 0, len + resultOffset);}

public String toUpperCase() {

return toUpperCase(Locale.getDefault());}

public String trim() {

int len = value.length;int st = 0;

char[] val = value;/* avoid getfield opcode */

while ((st ' ')) {st++;

}while ((st 1] ' ')) {

len--;}

return ((st > 0) || (len this;}

public String toString() {

return this;}

public char[] toCharArray() {

// Cannot use Arrays.copyOf because of class initialization order issueschar result[] = new char[value.length];

System.arraycopy(value, 0, result, 0, value.length);return result;

}

public static String format(String format, Object... args) {return new Formatter().format(format, args).toString();

}

public static String format(Locale l, String format, Object... args) {return new Formatter(l).format(format, args).toString();

}

public static String valueOf(Object obj) {return (obj == null) ? "null" : obj.toString();

}

public static String valueOf(char data[]) {return new String(data);

}

public static String valueOf(char data[], int offset, int count) {return new String(data, offset, count);

}

public static String copyValueOf(char data[], int offset, int count) {// All public String constructors now copy the data.

return new String(data, offset, count);}

public static String copyValueOf(char data[]) {

return new String(data);}

public static String valueOf(boolean b) {

return b ? "true" : "false";}

public static String valueOf(char c) {

char data[] = {c};return new String(data, true);

}

public static String valueOf(int i) {return Integer.toString(i);

}

public static String valueOf(long l) {return Long.toString(l);

}

public static String valueOf(float f) {return Float.toString(f);

}

public static String valueOf(double d) {return Double.toString(d);

}

public native String intern();

private static final int HASHING_SEED;

static {long nanos = System.nanoTime();

long now = System.currentTimeMillis();int SEED_MATERIAL[] = {

System.identityHashCode(String.class),System.identityHashCode(System.class),

(int) (nanos >>> 32),(int) nanos,

(int) (now >>> 32),(int) now,

(int) (System.nanoTime() >>> 2)};

// Use murmur3 to scramble the seeding material.

// Inline implementation to avoid loading classesint h1 = 0;

// body

for (int k1 : SEED_MATERIAL) {k1 *= 0xcc9e2d51;

k1 = (k1 15) | (k1 >>> 17);k1 *= 0x1b873593;

h1 ^= k1;

h1 = (h1 13) | (h1 >>> 19);h1 = h1 * 5 + 0xe6546b64;

}

// tail (always empty, as body is always 32-bit chunks)

// finalization

h1 ^= SEED_MATERIAL.length * 4;

// finalization mix force all bits of a hash block to avalancheh1 ^= h1 >>> 16;

h1 *= 0x85ebca6b;h1 ^= h1 >>> 13;

h1 *= 0xc2b2ae35;h1 ^= h1 >>> 16;

HASHING_SEED = h1;

}

private transient int hash32 = 0;

int hash32() {

int h = hash32;if (0 == h) {

// harmless data race on hash32 here.h = sun.misc.Hashing.murmur3_32(HASHING_SEED, value, 0, value.length);

// ensure result is not zero to avoid recalcing

h = (0 != h) ? h : 1;

hash32 = h;}

return h;

}}

阐明:String的本色是字符序列,它是经由过程字符数组实现的!

3. String 将各类工具转换成String的API

源码如下(StringValueTest.java):

/**

* String value相关示例*

* @author skywang*/

import java.util.HashMap;

public class StringValueTest {

public static void main(String[] args) {testValueAPIs() ;

}

/奸淫 String 的valueOf()演示法度榜样

*/private static void testValueAPIs() {

System.out.println("-------------------------------- testValueAPIs --------------------------------");// 1. StringvalueOf(Object obj)

//实际上,返回的是obj.toString();HashMap map = new HashMap();

map.put("1", "one");map.put("2", "two");

map.put("3", "three");System.out.printf("%-50s = %s\n", "String.valueOf(map)", String.valueOf(map));

// 2.StringvalueOf(boolean b)

System.out.printf("%-50s = %s\n", "String.valueOf(true)", String.valueOf(true));

// 3.StringvalueOf(char c)System.out.printf("%-50s = %s\n", "String.valueOf('m')", String.valueOf('m'));

// 4.StringvalueOf(int i)

System.out.printf("%-50s = %s\n", "String.valueOf(96)", String.valueOf(96));

// 5.StringvalueOf(long l)System.out.printf("%-50s = %s\n", "String.valueOf(12345L)", String.valueOf(12345L));

// 6.StringvalueOf(float f)

System.out.printf("%-50s = %s\n", "String.valueOf(1.414f)", String.valueOf(1.414f));

// 7.StringvalueOf(double d)System.out.printf("%-50s = %s\n", "String.valueOf(3.14159d)", String.valueOf(3.14159d));

// 8.StringvalueOf(char[] data)

System.out.printf("%-50s = %s\n", "String.valueOf(new char[]{'s','k','y'})", String.valueOf(new char[]{'s','k','y'}));

// 9.StringvalueOf(char[] data, int offset, int count)System.out.printf("%-50s = %s\n", "String.valueOf(new char[]{'s','k','y'}, 0, 2)", String.valueOf(new char[]{'s','k','y'}, 0, 2));

System.out.println();

}}

运行结果:

-------------------------------- testValueAPIs --------------------------------

String.valueOf(map)= {3=three, 2=two, 1=one}String.valueOf(true)= true

String.valueOf('m')= mString.valueOf(96)= 96

String.valueOf(12345L)= 12345String.valueOf(1.414f)= 1.414

String.valueOf(3.14159d)= 3.14159String.valueOf(new char[]{'s','k','y'})= sky

String.valueOf(new char[]{'s','k','y'}, 0, 2)= sk

4. String 中index相关的API

源码如下(StringIndexTest.java):

/**

* String 中index相关API演示*

* @author skywang*/

public class StringIndexTest {

public static void main(String[] args) {

testIndexAPIs() ;}

/**

* String 中index相关API演示*/

private static void testIndexAPIs() {System.out.println("-------------------------------- testIndexAPIs --------------------------------");

String istr = "abcAbcABCabCaBcAbCaBCabc";

System.out.printf("istr=%s\n", istr);

// 1. 早年以后,找出‘a’第一次呈现的位置System.out.printf("%-30s = %d\n", "istr.indexOf((int)'a')", istr.indexOf((int)'a'));

// 2. 从位置5开始,早年以后,找出‘a’第一次呈现的位置

System.out.printf("%-30s = %d\n", "istr.indexOf((int)'a', 5)", istr.indexOf((int)'a', 5));

// 3. 从后往前,找出‘a’第一次呈现的位置System.out.printf("%-30s = %d\n", "istr.lastIndexOf((int)'a')", istr.lastIndexOf((int)'a'));

// 4. 从位置10开始,从后往前,找出‘a’第一次呈现的位置

System.out.printf("%-30s = %d\n", "istr.lastIndexOf((int)'a', 10)", istr.lastIndexOf((int)'a', 10));

// 5. 早年以后,找出"bc"第一次呈现的位置

System.out.printf("%-30s = %d\n", "istr.indexOf(\"bc\")", istr.indexOf("bc"));

// 6. 从位置5开始,早年以后,找出"bc"第一次呈现的位置System.out.printf("%-30s = %d\n", "istr.indexOf(\"bc\", 5)", istr.indexOf("bc", 5));

// 7. 从后往前,找出"bc"第一次呈现的位置

System.out.printf("%-30s = %d\n", "istr.lastIndexOf(\"bc\")", istr.lastIndexOf("bc"));

// 8. 从位置4开始,从后往前,找出"bc"第一次呈现的位置System.out.printf("%-30s = %d\n", "istr.lastIndexOf(\"bc\", 4)", istr.lastIndexOf("bc", 4));

System.out.println();

}}

运行结果:

-------------------------------- testIndexAPIs --------------------------------

istr=abcAbcABCabCaBcAbCaBCabc

istr.indexOf((int)'a')= 0

istr.indexOf((int)'a', 5)= 9

istr.lastIndexOf((int)'a')= 21

istr.lastIndexOf((int)'a', 10) = 9

istr.indexOf("bc")= 1

istr.indexOf("bc", 5)= 22

istr.lastIndexOf("bc")= 22

istr.lastIndexOf("bc", 4)= 4

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