String详解, String和CharSequence区别, StringBuilder和StringBuffer的区别 (String系列之1)

1. String 简介
    String 是java中的字符串，它继承于CharSequence。String类所包含的API接口非常多。为了便于今后的使用，我对String的API进行了分类，并都给出的演示程序。

  1.1 String 和 CharSequence 关系
    String 继承于CharSequence，也就是说String也是CharSequence类型。CharSequence是一个接口，它只包括length(), charAt(int index), subSequence(int start, int end)这几个API接口。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！
  1.2 StringBuilder 和 StringBuffer 的区别
    StringBuilder 和 StringBuffer都是可变的字符序列。它们都继承于AbstractStringBuilder，实现了CharSequence接口。但是，StringBuilder是非线程安全的，而StringBuffer是线程安全的。

String 函数列表 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()

2. 演示程序CharSequence下面通过示例，演示CharSequence的使用方法！

 /** 2  * CharSequence 演示程序 3  * 4  *  5  */ 6 import java.nio.charset.Charset; 7 import java.io.UnsupportedEncodingException; 8  9 public class CharSequenceTest {10 11     public static void main(String[] args) {12         testCharSequence();13     }14 15     /**16      * CharSequence 测试程序17      */18     private static void testCharSequence() {19         System.out.println("-------------------------------- testCharSequence -----------------------------");20 21         // 1. CharSequence的子类String22         String str = "abcdefghijklmnopqrstuvwxyz";23         System.out.println("1. String");24         System.out.printf("   %-30s=%d\n", "str.length()", str.length());25         System.out.printf("   %-30s=%c\n", "str.charAt(5)", str.charAt(5));26         String substr = (String)str.subSequence(0,5);27         System.out.printf("   %-30s=%s\n", "str.subSequence(0,5)", substr.toString());28 29         // 2. CharSequence的子类StringBuilder30         StringBuilder strbuilder = new StringBuilder("abcdefghijklmnopqrstuvwxyz");31         System.out.println("2. StringBuilder");32         System.out.printf("   %-30s=%d\n", "strbuilder.length()", strbuilder.length());33         System.out.printf("   %-30s=%c\n", "strbuilder.charAt(5)", strbuilder.charAt(5));34         // 注意：StringBuilder的subSequence()返回的是，实际上是一个String对象！35         String substrbuilder = (String)strbuilder.subSequence(0,5);36         System.out.printf("   %-30s=%s\n", "strbuilder.subSequence(0,5)", substrbuilder.toString());37 38         // 3. CharSequence的子类StringBuffer39         StringBuffer strbuffer = new StringBuffer("abcdefghijklmnopqrstuvwxyz");40         System.out.println("3. StringBuffer");41         System.out.printf("   %-30s=%d\n", "strbuffer.length()", strbuffer.length());42         System.out.printf("   %-30s=%c\n", "strbuffer.charAt(5)", strbuffer.charAt(5));43         // 注意：StringBuffer的subSequence()返回的是，实际上是一个String对象！44         String substrbuffer = (String)strbuffer.subSequence(0,5);45         System.out.printf("   %-30s=%s\n", "strbuffer.subSequence(0,5)", substrbuffer.toString());46 47         System.out.println();48     }49 }

运行结果：-------------------------------- testCharSequence -----------------------------1. String   str.length()                  =26   str.charAt(5)                 =f   str.subSequence(0,5)          =abcde2. StringBuilder   strbuilder.length()           =26   strbuilder.charAt(5)          =f   strbuilder.subSequence(0,5)   =abcde3. StringBuffer   strbuffer.length()            =26   strbuffer.charAt(5)           =f   strbuffer.subSequence(0,5)    =abcde

3. String 构造函数

/** 2  * String 构造函数演示程序 5  */ 6 import java.nio.charset.Charset; 7 import java.io.UnsupportedEncodingException; 8  9 public class StringContructorTest {10 11     public static void main(String[] args) {12         testStringConstructors() ;13     }14 15     /**16      * String 构造函数测试程序17      */18     private static void testStringConstructors() {19         try {20             System.out.println("-------------------------------- testStringConstructors -----------------------");21 22             String str01 = new String();23             String str02 = new String("String02");24             String str03 = new String(new char[]{'s','t','r','0','3'});25             String str04 = new String(new char[]{'s','t','r','0','4'}, 1, 3);          // 1表示起始位置，3表示个数26             String str05 = new String(new byte[]{0x61, 0x62, 0x63, 0x64, 0x65});       // 0x61在ASC表中，对应字符"a"; 1表示起始位置，3表示长度27             String str06 = new String(new byte[]{0x61, 0x62, 0x63, 0x64, 0x65}, 1, 3); // 0x61在ASC表中，对应字符"a"; 1表示起始位置，3表示长度28             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”29             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表示起始位置，3表示长度30             String str09 = new String(new byte[]{(byte)0xe5, (byte)0xad, (byte)0x97, /* 字-对应的utf-8编码 */ 31                                                  (byte)0xe7, (byte)0xac, (byte)0xa6, /* 符-对应的utf-8编码 */ 32                                                  (byte)0xe7, (byte)0xbc, (byte)0x96, /* 编-对应的utf-8编码 */ 33                                                  (byte)0xe7, (byte)0xa0, (byte)0x81, /* 码-对应的utf-8编码 */ }, 34                                       0, 12, "utf-8");  // 0表示起始位置，12表示长度。35             String str10 = new String(new byte[]{(byte)0x5b, (byte)0x57, /* 字-对应的utf-16编码 */ 36                                                  (byte)0x7b, (byte)0x26, /* 符-对应的utf-16编码 */ 37                                                  (byte)0x7f, (byte)0x16, /* 编-对应的utf-16编码 */ 38                                                  (byte)0x78, (byte)0x01, /* 码-对应的utf-16编码 */ }, 39                                       0, 8, "utf-16");  // 0表示起始位置，8表示长度。40             String str11 = new String(new byte[]{(byte)0xd7, (byte)0xd6, /* 字-对应的gb2312编码  */ 41                                                  (byte)0xb7, (byte)0xfb, /* 符-对应的gb2312编码 */ 42                                                  (byte)0xb1, (byte)0xe0, /* 编-对应的gb2312编码 */ 43                                                  (byte)0xc2, (byte)0xeb, /* 码-对应的gb2312编码 */ }, 44                                       Charset.forName("gb2312")); 45             String str12 = new String(new byte[]{(byte)0xd7, (byte)0xd6, /* 字-对应的gbk编码 */ 46                                                  (byte)0xb7, (byte)0xfb, /* 符-对应的gbk编码 */ 47                                                  (byte)0xb1, (byte)0xe0, /* 编-对应的gbk编码 */ 48                                                  (byte)0xc2, (byte)0xeb, /* 码-对应的gbk编码 */ }, 49                                       0, 8, Charset.forName("gbk")); 50             String str13 = new String(new int[] {0x5b57, 0x7b26, 0x7f16, 0x7801}, 0, 4);  // "字符编码"(\u5b57是‘字’的unicode编码)。0表示起始位置，4表示长度。51             String str14 = new String(new StringBuffer("StringBuffer"));52             String str15 = new String(new StringBuilder("StringBuilder"));53 54             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",55                     str01, str02, str03, str04, str05, str06, str07, str08, str09, str10, str11, str12, str13, str14, str15);56 57 58             System.out.println();59         } catch (UnsupportedEncodingException e) {60             e.printStackTrace();61         }62     }63 }

运行结果:-------------------------------- testStringConstructors ----------------------- str01=  str02=String02  str03=str03  str04=tr0  str05=abcde  str06=bcd  str07=abcde  str08=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

4. String 将各种对象转换成String的API

/** 2  * String value相关示例 5  */ 6 import java.util.HashMap; 7  8 public class StringValueTest { 9     10     public static void main(String[] args) {11         testValueAPIs() ;12     }13 14     /**15      * String 的valueOf()演示程序16      */17     private static void testValueAPIs() {18         System.out.println("-------------------------------- testValueAPIs --------------------------------");19         // 1. String    valueOf(Object obj)20         //  实际上，返回的是obj.toString();21         HashMap map = new HashMap();22         map.put("1", "one");23         map.put("2", "two");24         map.put("3", "three");25         System.out.printf("%-50s = %s\n", "String.valueOf(map)", String.valueOf(map));26 27         // 2.String    valueOf(boolean b)28         System.out.printf("%-50s = %s\n", "String.valueOf(true)", String.valueOf(true));29 30         // 3.String    valueOf(char c)31         System.out.printf("%-50s = %s\n", "String.valueOf('m')", String.valueOf('m'));32 33         // 4.String    valueOf(int i)34         System.out.printf("%-50s = %s\n", "String.valueOf(96)", String.valueOf(96));35 36         // 5.String    valueOf(long l)37         System.out.printf("%-50s = %s\n", "String.valueOf(12345L)", String.valueOf(12345L));38 39         // 6.String    valueOf(float f)40         System.out.printf("%-50s = %s\n", "String.valueOf(1.414f)", String.valueOf(1.414f));41 42         // 7.String    valueOf(double d)43         System.out.printf("%-50s = %s\n", "String.valueOf(3.14159d)", String.valueOf(3.14159d));44 45         // 8.String    valueOf(char[] data)46         System.out.printf("%-50s = %s\n", "String.valueOf(new char[]{'s','k','y'})", String.valueOf(new char[]{'s','k','y'}));47 48         // 9.String    valueOf(char[] data, int offset, int count)49         System.out.printf("%-50s = %s\n", "String.valueOf(new char[]{'s','k','y'}, 0, 2)", String.valueOf(new char[]{'s','k','y'}, 0, 2));50 51         System.out.println();52     }53 }

运行结果:-------------------------------- testValueAPIs --------------------------------String.valueOf(map)                                = {3=three, 2=two, 1=one}String.valueOf(true)                               = trueString.valueOf('m')                                = mString.valueOf(96)                                 = 96String.valueOf(12345L)                             = 12345String.valueOf(1.414f)                             = 1.414String.valueOf(3.14159d)                           = 3.14159String.valueOf(new char[]{'s','k','y'})            = skyString.valueOf(new char[]{'s','k','y'}, 0, 2)      = sk

5. String 中index相关的API

/** 2  * String 中index相关API演示 3  * 4  * @author skywang 5  */ 6  7 public class StringIndexTest { 8  9     public static void main(String[] args) {10         testIndexAPIs() ;11     }12 13     /**14      * String 中index相关API演示15      */16     private static void testIndexAPIs() {17         System.out.println("-------------------------------- testIndexAPIs --------------------------------");18 19         String istr = "abcAbcABCabCaBcAbCaBCabc";20         System.out.printf("istr=%s\n", istr);23         System.out.printf("%-30s = %d\n", "istr.indexOf((int)'a')", istr.indexOf((int)'a'));26         System.out.printf("%-30s = %d\n", "istr.indexOf((int)'a', 5)", istr.indexOf((int)'a', 5));29         System.out.printf("%-30s = %d\n", "istr.lastIndexOf((int)'a')", istr.lastIndexOf((int)'a'));32         System.out.printf("%-30s = %d\n", "istr.lastIndexOf((int)'a', 10)", istr.lastIndexOf((int)'a', 10));36         System.out.printf("%-30s = %d\n", "istr.indexOf(\"bc\")", istr.indexOf("bc"));39         System.out.printf("%-30s = %d\n", "istr.indexOf(\"bc\", 5)", istr.indexOf("bc", 5));42         System.out.printf("%-30s = %d\n", "istr.lastIndexOf(\"bc\")", istr.lastIndexOf("bc"));45         System.out.printf("%-30s = %d\n", "istr.lastIndexOf(\"bc\", 4)", istr.lastIndexOf("bc", 4));46 47         System.out.println();48     }49 }

运行结果:-------------------------------- testIndexAPIs --------------------------------istr=abcAbcABCabCaBcAbCaBCabcistr.indexOf((int)'a')         = 0istr.indexOf((int)'a', 5)      = 9istr.lastIndexOf((int)'a')     = 21istr.lastIndexOf((int)'a', 10) = 9istr.indexOf("bc")             = 1istr.indexOf("bc", 5)          = 22istr.lastIndexOf("bc")         = 22istr.lastIndexOf("bc", 4)      = 4

6. String “比较”操作的API

 1 /** 2  * String 中比较相关API演示 3  * 4  * @author skywang 5  */ 6  7 public class StringCompareTest { 8  9     public static void main(String[] args) {10         testCompareAPIs() ;11     }12 13     /**14      * String 中比较相关API演示15      */16     private static void testCompareAPIs() {17         System.out.println("-------------------------------- testCompareAPIs ------------------------------");18 19         //String str = "abcdefghijklmnopqrstuvwxyz";20         String str = "abcAbcABCabCAbCabc";21         System.out.printf("str=%s\n", str);22 23         // 1. 比较“2个String是否相等”24         System.out.printf("%-50s = %b\n", 25                 "str.equals(\"abcAbcABCabCAbCabc\")", 26                 str.equals("abcAbcABCabCAbCabc"));27 28         // 2. 比较“2个String是否相等(忽略大小写)”29         System.out.printf("%-50s = %b\n", 30                 "str.equalsIgnoreCase(\"ABCABCABCABCABCABC\")", 31                 str.equalsIgnoreCase("ABCABCABCABCABCABC"));32 33         // 3. 比较“2个String的大小”34         System.out.printf("%-40s = %d\n", "str.compareTo(\"abce\")", str.compareTo("abce"));35 36         // 4. 比较“2个String的大小(忽略大小写)”37         System.out.printf("%-40s = %d\n", "str.compareToIgnoreCase(\"ABC\")", str.compareToIgnoreCase("ABC"));38 39         // 5. 字符串的开头是不是"ab"40         System.out.printf("%-40s = %b\n", "str.startsWith(\"ab\")", str.startsWith("ab"));41 42         // 6. 字符串的从位置3开头是不是"ab"43         System.out.printf("%-40s = %b\n", "str.startsWith(\"Ab\")", str.startsWith("Ab", 3));44 45         // 7. 字符串的结尾是不是"bc"46         System.out.printf("%-40s = %b\n", "str.endsWith(\"bc\")", str.endsWith("bc"));47 48         // 8. 字符串的是不是包含"ABC"49         System.out.printf("%-40s = %b\n", "str.contains(\"ABC\")", str.contains("ABC"));50 51         // 9. 比较2个字符串的部分内容52         String region1 = str.substring(2, str.length());    // 获取str位置3(包括)到末尾(不包括)的子字符串53         // 将“str中从位置2开始的字符串”和“region1中位置0开始的字符串”进行比较，比较长度是5。54         System.out.printf("regionMatches(%s) = %b\n", region1, 55                 str.regionMatches(2, region1, 0, 5));56 57         // 10. 比较2个字符串的部分内容(忽略大小写)58         String region2 = region1.toUpperCase();    // 将region1转换为大写59         String region3 = region1.toLowerCase();    // 将region1转换为小写60         System.out.printf("regionMatches(%s) = %b\n", region2, 61                 str.regionMatches(2, region2, 0, 5));62         System.out.printf("regionMatches(%s) = %b\n", region3, 63                 str.regionMatches(2, region3, 0, 5));64 65         // 11. 比较“String”和“StringBuffer”的内容是否相等66         System.out.printf("%-60s = %b\n", 67                 "str.contentEquals(new StringBuffer(\"abcAbcABCabCAbCabc\"))", 68                 str.contentEquals(new StringBuffer("abcAbcABCabCAbCabc")));69 70         // 12. 比较“String”和“StringBuilder”的内容是否相等71         System.out.printf("%-60s = %b\n", 72                 "str.contentEquals(new StringBuilder(\"abcAbcABCabCAbCabc\"))", 73                 str.contentEquals(new StringBuilder("abcAbcABCabCAbCabc")));74 75         // 13. match()测试程序76         // 正则表达式 xxx.xxx.xxx.xxx，其中xxx中x的取值可以是0～9，xxx中有1～3位。77         String reg_ipv4 = "[0-9]{3}(\\.[0-9]{1,3}){3}";    78 79         String ipv4addr1 = "192.168.1.102";80         String ipv4addr2 = "192.168";81         System.out.printf("%-40s = %b\n", "ipv4addr1.matches()", ipv4addr1.matches(reg_ipv4));82         System.out.printf("%-40s = %b\n", "ipv4addr2.matches()", ipv4addr2.matches(reg_ipv4));83 84         System.out.println();85     }86 }

运行结果：-------------------------------- testCompareAPIs ------------------------------str=abcAbcABCabCAbCabcstr.equals("abcAbcABCabCAbCabc")                   = truestr.equalsIgnoreCase("ABCABCABCABCABCABC")         = truestr.compareTo("abce")                    = -36str.compareToIgnoreCase("ABC")           = 15str.startsWith("ab")                     = truestr.startsWith("Ab")                     = truestr.endsWith("bc")                       = truestr.contains("ABC")                      = trueregionMatches(cAbcABCabCAbCabc) = trueregionMatches(CABCABCABCABCABC) = falseregionMatches(cabcabcabcabcabc) = falsestr.contentEquals(new StringBuffer("abcAbcABCabCAbCabc"))    = truestr.contentEquals(new StringBuilder("abcAbcABCabCAbCabc"))   = trueipv4addr1.matches()                      = trueipv4addr2.matches()                      = false

7. String “修改(追加/替换/截取/分割)”操作的API

/** 2  * String 中 修改(追加/替换/截取/分割)字符串的相关API演示 3  * 4  * @author skywang 5  */ 6  7 public class StringModifyTest { 8      9     public static void main(String[] args) {10         testModifyAPIs() ;11     }12 13     /**14      * String 中 修改(追加/替换/截取/分割)字符串的相关API演示15      */16     private static void testModifyAPIs() {17         System.out.println("-------------------------------- testModifyAPIs -------------------------------");18 19         String str = " abcAbcABCabCAbCabc ";20         System.out.printf("str=%s, len=%d\n", str, str.length());21 22         // 1.追加23         // 将"123"追加到str之后24         System.out.printf("%-30s = %s\n", "str.concat(\"123\")", 25                 str.concat("123"));26 27         // 2.截取28         // 截取str中从位置7(包括)开始的元素。29         System.out.printf("%-30s = %s\n", "str.substring(7)", str.substring(7));30         // 截取str中从位置7(包括)到位置10(不包括)之间的元素。31         System.out.printf("%-30s = %s\n", "str.substring(7, 10)", str.substring(7, 10));32         // 删除str中首位的空格，并返回。33         System.out.printf("%-30s = %s, len=%d\n", "str.trim()", str.trim(), str.trim().length());34 35         // 3.替换36         // 将str中的 “字符‘a’” 全部替换为 “字符‘_’”37         System.out.printf("%-30s = %s\n", "str.replace('a', 'M')", str.replace('a', '_'));38         // 将str中的第一次出现的“字符串“a”” 替换为 “字符串“###””39         System.out.printf("%-30s = %s\n", "str.replaceFirst(\"a\", \"###\")", str.replaceFirst("a", "###"));40         // 将str中的 “字符串“a”” 全部替换为 “字符串“$$$””41         System.out.printf("%-30s = %s\n", "str.replace(\"a\", \"$$$\")", str.replace("a", "$$$"));42 43         // 4.分割44         // 以“b”作为分隔符，对str进行分割45         String[] splits = str.split("b");46         for (int i=0; i<splits.length; i++) {47             System.out.printf("splits[%d]=%s\n", i, splits[i]);48         }49 50         System.out.println();51     }52 }

运行结果：-------------------------------- testModifyAPIs -------------------------------str= abcAbcABCabCAbCabc , len=20str.concat("123")              =  abcAbcABCabCAbCabc 123str.substring(7)               = ABCabCAbCabc str.substring(7, 10)           = ABCstr.trim()                     = abcAbcABCabCAbCabc, len=18str.replace('a', 'M')          =  _bcAbcABC_bCAbC_bc str.replaceFirst("a", "###")   =  ###bcAbcABCabCAbCabc str.replace("a", "$$$")        =  $$$bcAbcABC$$$bCAbC$$$bc splits[0]= asplits[1]=cAsplits[2]=cABCasplits[3]=CAsplits[4]=Casplits[5]=c

运行结果：-------------------------------- testUnicodeAPIs ------------------------------ustr=字符编码ustr.codePointAt(0)            = 0x5b57ustr.codePointBefore(2)        = 0x7b26ustr.offsetByCodePoints(1, 2)  = 3ustr.codePointCount(0, 3)      = 3

8. String 剩余的API

/** 2  * String 中其它的API 3  * 4  * @author skywang 5  */ 6  7 public class StringOtherTest { 8      9     public static void main(String[] args) {10         testOtherAPIs() ;11     }12 13     /**14      * String 中其它的API15      */16     private static void testOtherAPIs() {17         System.out.println("-------------------------------- testOtherAPIs --------------------------------");18 19         String str = "0123456789";20         System.out.printf("str=%s\n", str);21 22         // 1. 字符串长度23         System.out.printf("%s = %d\n", "str.length()", str.length());24 25         // 2. 字符串是否为空26         System.out.printf("%s = %b\n", "str.isEmpty()", str.isEmpty());27 28         // 3. [字节] 获取字符串对应的字节数组29         byte[] barr = str.getBytes();30         for (int i=0; i<barr.length; i++) {31                System.out.printf("barr[%d]=0x%x ", i, barr[i]);32         }33         System.out.println();34 35         // 4. [字符] 获取字符串位置4的字符36         System.out.printf("%s = %c\n", "str.charAt(4)", str.charAt(4));37 38         // 5. [字符] 获取字符串对应的字符数组39         char[] carr = str.toCharArray();40         for (int i=0; i<carr.length; i++) {41                System.out.printf("carr[%d]=%c ", i, carr[i]);42         }43         System.out.println();44 45         // 6. [字符] 获取字符串中部分元素对应的字符数组46         char[] carr2 = new char[3];47         str.getChars(6, 9, carr2, 0);48         for (int i=0; i<carr2.length; i++) {49                System.out.printf("carr2[%d]=%c ", i, carr2[i]);50         }51         System.out.println();52 53         // 7. [字符] 获取字符数组对应的字符串54         System.out.printf("%s = %s\n", 55                 "str.copyValueOf(new char[]{'a','b','c','d','e'})", 56                 String.copyValueOf(new char[]{'a','b','c','d','e'}));57 58         // 8. [字符] 获取字符数组中部分元素对应的字符串59         System.out.printf("%s = %s\n", 60                 "str.copyValueOf(new char[]{'a','b','c','d','e'}, 1, 4)", 61                 String.copyValueOf(new char[]{'a','b','c','d','e'}, 1, 4));62 63         // 9. format()示例，将对象数组按指定格式转换为字符串64         System.out.printf("%s = %s\n", 65                 "str.format()", 66                 String.format("%s-%d-%b", "abc", 3, true));67 68         System.out.println();69     }70 }

运行结果：-------------------------------- testOtherAPIs --------------------------------str=0123456789str.length() = 10str.isEmpty() = falsebarr[0]=0x30 barr[1]=0x31 barr[2]=0x32 barr[3]=0x33 barr[4]=0x34 barr[5]=0x35 barr[6]=0x36 barr[7]=0x37 barr[8]=0x38 barr[9]=0x39 str.charAt(4) = 4carr[0]=0 carr[1]=1 carr[2]=2 carr[3]=3 carr[4]=4 carr[5]=5 carr[6]=6 carr[7]=7 carr[8]=8 carr[9]=9 carr2[0]=6 carr2[1]=7 carr2[2]=8 str.copyValueOf(new char[]{'a','b','c','d','e'}) = abcdestr.copyValueOf(new char[]{'a','b','c','d','e'}, 1, 4) = bcdestr.format() = abc-3-true

9. String 完整示例

/**  2  * String 演示程序  3  *  4  * @author skywang  5  */  6 import java.util.HashMap;  7 import java.nio.charset.Charset;  8 import java.io.UnsupportedEncodingException;  9  10 public class StringAPITest { 11      12     public static void main(String[] args) { 13         testStringConstructors() ; // String 构造函数测试程序 14         testValueAPIs() ;          // String 的valueOf()演示程序 15         testIndexAPIs() ;          // String 中index相关API演示 16         testCompareAPIs() ;        // String 中比较相关API演示 17         testModifyAPIs() ;         // String 中 修改(追加/替换/截取/分割)字符串的相关API演示 18         testUnicodeAPIs() ;        // String 中与unicode相关的API 19         testOtherAPIs() ;          // String 中其它的API 20     } 21  22     /** 23      * String 构造函数测试程序 24      */ 25     private static void testStringConstructors() { 26         try { 27             System.out.println("-------------------------------- testStringConstructors -----------------------"); 28  29             String str01 = new String(); 30             String str02 = new String("String02"); 31             String str03 = new String(new char[]{'s','t','r','0','3'}); 32             String str04 = new String(new char[]{'s','t','r','0','4'}, 1, 3);          // 1表示起始位置，3表示个数 33             String str05 = new String(new byte[]{0x61, 0x62, 0x63, 0x64, 0x65});       // 0x61在ASC表中，对应字符"a"; 1表示起始位置，3表示长度 34             String str06 = new String(new byte[]{0x61, 0x62, 0x63, 0x64, 0x65}, 1, 3); // 0x61在ASC表中，对应字符"a"; 1表示起始位置，3表示长度 35             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” 36             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表示起始位置，3表示长度 37             String str09 = new String(new byte[]{(byte)0xe5, (byte)0xad, (byte)0x97, /* 字-对应的utf-8编码 */  38                                                  (byte)0xe7, (byte)0xac, (byte)0xa6, /* 符-对应的utf-8编码 */  39                                                  (byte)0xe7, (byte)0xbc, (byte)0x96, /* 编-对应的utf-8编码 */  40                                                  (byte)0xe7, (byte)0xa0, (byte)0x81, /* 码-对应的utf-8编码 */ },  41                                       0, 12, "utf-8");  // 0表示起始位置，12表示长度。 42             String str10 = new String(new byte[]{(byte)0x5b, (byte)0x57, /* 字-对应的utf-16编码 */  43                                                  (byte)0x7b, (byte)0x26, /* 符-对应的utf-16编码 */  44                                                  (byte)0x7f, (byte)0x16, /* 编-对应的utf-16编码 */  45                                                  (byte)0x78, (byte)0x01, /* 码-对应的utf-16编码 */ },  46                                       0, 8, "utf-16");  // 0表示起始位置，8表示长度。 47             String str11 = new String(new byte[]{(byte)0xd7, (byte)0xd6, /* 字-对应的gb2312编码  */  48                                                  (byte)0xb7, (byte)0xfb, /* 符-对应的gb2312编码 */  49                                                  (byte)0xb1, (byte)0xe0, /* 编-对应的gb2312编码 */  50                                                  (byte)0xc2, (byte)0xeb, /* 码-对应的gb2312编码 */ },  51                                       Charset.forName("gb2312"));  52             String str12 = new String(new byte[]{(byte)0xd7, (byte)0xd6, /* 字-对应的gbk编码 */  53                                                  (byte)0xb7, (byte)0xfb, /* 符-对应的gbk编码 */  54                                                  (byte)0xb1, (byte)0xe0, /* 编-对应的gbk编码 */  55                                                  (byte)0xc2, (byte)0xeb, /* 码-对应的gbk编码 */ },  56                                       0, 8, Charset.forName("gbk"));  57             String str13 = new String(new int[] {0x5b57, 0x7b26, 0x7f16, 0x7801}, 0, 4);  // "字符编码"(\u5b57是‘字’的unicode编码)。0表示起始位置，4表示长度。 58             String str14 = new String(new StringBuffer("StringBuffer")); 59             String str15 = new String(new StringBuilder("StringBuilder")); 60  61             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", 62                     str01, str02, str03, str04, str05, str06, str07, str08, str09, str10, str11, str12, str13, str14, str15); 63  64  65             System.out.println(); 66         } catch (UnsupportedEncodingException e) { 67             e.printStackTrace(); 68         } 69     } 70  71     /** 72      * String 中其它的API 73      */ 74     private static void testOtherAPIs() { 75         System.out.println("-------------------------------- testOtherAPIs --------------------------------"); 76  77         String str = "0123456789"; 78         System.out.printf("str=%s\n", str); 79  80         // 1. 字符串长度 81         System.out.printf("%s = %d\n", "str.length()", str.length()); 82  83         // 2. 字符串是否为空 84         System.out.printf("%s = %b\n", "str.isEmpty()", str.isEmpty()); 85  86         // 3. [字节] 获取字符串对应的字节数组 87         byte[] barr = str.getBytes(); 88         for (int i=0; i<barr.length; i++) { 89                System.out.printf("barr[%d]=0x%x ", i, barr[i]); 90         } 91         System.out.println(); 92  93         // 4. [字符] 获取字符串位置4的字符 94         System.out.printf("%s = %c\n", "str.charAt(4)", str.charAt(4)); 95  96         // 5. [字符] 获取字符串对应的字符数组 97         char[] carr = str.toCharArray(); 98         for (int i=0; i<carr.length; i++) { 99                System.out.printf("carr[%d]=%c ", i, carr[i]);100         }101         System.out.println();102 103         // 6. [字符] 获取字符串中部分元素对应的字符数组104         char[] carr2 = new char[3];105         str.getChars(6, 9, carr2, 0);106         for (int i=0; i<carr2.length; i++) {107                System.out.printf("carr2[%d]=%c ", i, carr2[i]);108         }109         System.out.println();110 111         // 7. [字符] 获取字符数组对应的字符串112         System.out.printf("%s = %s\n", 113                 "str.copyValueOf(new char[]{'a','b','c','d','e'})", 114                 String.copyValueOf(new char[]{'a','b','c','d','e'}));115 116         // 8. [字符] 获取字符数组中部分元素对应的字符串117         System.out.printf("%s = %s\n", 118                 "str.copyValueOf(new char[]{'a','b','c','d','e'}, 1, 4)", 119                 String.copyValueOf(new char[]{'a','b','c','d','e'}, 1, 4));120 121         // 9. format()示例，将对象数组按指定格式转换为字符串122         System.out.printf("%s = %s\n", 123                 "str.format()", 124                 String.format("%s-%d-%b", "abc", 3, true));125 126         System.out.println();127     }128 129     /**130      * String 中 修改(追加/替换/截取/分割)字符串的相关API演示131      */132     private static void testModifyAPIs() {133         System.out.println("-------------------------------- testModifyAPIs -------------------------------");134 135         String str = " abcAbcABCabCAbCabc ";136         System.out.printf("%s, len=%d\n", str, str.length());137 138         // 1.追加139         // 将"123"追加到str之后140         System.out.printf("%-30s = %s\n", "str.concat(\"123\")", 141                 str.concat("123"));142 143         // 2.截取144         // 截取str中从位置7(包括)开始的元素。145         System.out.printf("%-30s = %s\n", "str.substring(7)", str.substring(7));146         // 截取str中从位置7(包括)到位置10(不包括)之间的元素。147         System.out.printf("%-30s = %s\n", "str.substring(7, 10)", str.substring(7, 10));148         // 删除str中首位的空格，并返回。149         System.out.printf("%-30s = %s, len=%d\n", "str.trim()", str.trim(), str.trim().length());150 151         // 3.替换152         // 将str中的 “字符‘a’” 全部替换为 “字符‘_’”153         System.out.printf("%-30s = %s\n", "str.replace('a', 'M')", str.replace('a', '_'));154         // 将str中的第一次出现的“字符串“a”” 替换为 “字符串“###””155         System.out.printf("%-30s = %s\n", "str.replaceFirst(\"a\", \"###\")", str.replaceFirst("a", "###"));156         // 将str中的 “字符串“a”” 全部替换为 “字符串“$$$””157         System.out.printf("%-30s = %s\n", "str.replace(\"a\", \"$$$\")", str.replace("a", "$$$"));158 159         // 4.分割160         // 以“b”作为分隔符，对str进行分割161         String[] splits = str.split("b");162         for (int i=0; i<splits.length; i++) {163             System.out.printf("splits[%d]=%s\n", i, splits[i]);164         }165 166         System.out.println();167     }168 169 170     /**171      * String 中比较相关API演示172      */173     private static void testCompareAPIs() {174         System.out.println("-------------------------------- testCompareAPIs ------------------------------");175 176         //String str = "abcdefghijklmnopqrstuvwxyz";177         String str = "abcAbcABCabCAbCabc";178         System.out.printf("%s\n", str);179 180         // 1. 比较“2个String是否相等”181         System.out.printf("%-50s = %b\n", 182                 "str.equals(\"abcAbcABCabCAbCabc\")", 183                 str.equals("abcAbcABCabCAbCabc"));184 185         // 2. 比较“2个String是否相等(忽略大小写)”186         System.out.printf("%-50s = %b\n", 187                 "str.equalsIgnoreCase(\"ABCABCABCABCABCABC\")", 188                 str.equalsIgnoreCase("ABCABCABCABCABCABC"));189 190         // 3. 比较“2个String的大小”191         System.out.printf("%-40s = %d\n", "str.compareTo(\"abce\")", str.compareTo("abce"));192 193         // 4. 比较“2个String的大小(忽略大小写)”194         System.out.printf("%-40s = %d\n", "str.compareToIgnoreCase(\"ABC\")", str.compareToIgnoreCase("ABC"));195 196         // 5. 字符串的开头是不是"ab"197         System.out.printf("%-40s = %b\n", "str.startsWith(\"ab\")", str.startsWith("ab"));198 199         // 6. 字符串的从位置3开头是不是"ab"200         System.out.printf("%-40s = %b\n", "str.startsWith(\"Ab\")", str.startsWith("Ab", 3));201 202         // 7. 字符串的结尾是不是"bc"203         System.out.printf("%-40s = %b\n", "str.endsWith(\"bc\")", str.endsWith("bc"));204 205         // 8. 字符串的是不是包含"ABC"206         System.out.printf("%-40s = %b\n", "str.contains(\"ABC\")", str.contains("ABC"));207 208         // 9. 比较2个字符串的部分内容209         String region1 = str.substring(2, str.length());    // 获取str位置3(包括)到末尾(不包括)的子字符串210         // 将“str中从位置2开始的字符串”和“region1中位置0开始的字符串”进行比较，比较长度是5。211         System.out.printf("regionMatches(%s) = %b\n", region1, 212                 str.regionMatches(2, region1, 0, 5));213 214         // 10. 比较2个字符串的部分内容(忽略大小写)215         String region2 = region1.toUpperCase();    // 将region1转换为大写216         String region3 = region1.toLowerCase();    // 将region1转换为小写217         System.out.printf("regionMatches(%s) = %b\n", region2, 218                 str.regionMatches(2, region2, 0, 5));219         System.out.printf("regionMatches(%s) = %b\n", region3, 220                 str.regionMatches(2, region3, 0, 5));221 222         // 11. 比较“String”和“StringBuffer”的内容是否相等223         System.out.printf("%-60s = %b\n", 224                 "str.contentEquals(new StringBuffer(\"abcAbcABCabCAbCabc\"))", 225                 str.contentEquals(new StringBuffer("abcAbcABCabCAbCabc")));226 227         // 12. 比较“String”和“StringBuilder”的内容是否相等228         System.out.printf("%-60s = %b\n", 229                 "str.contentEquals(new StringBuilder(\"abcAbcABCabCAbCabc\"))", 230                 str.contentEquals(new StringBuilder("abcAbcABCabCAbCabc")));231 232         // 13. match()测试程序233         // 正则表达式 xxx.xxx.xxx.xxx，其中xxx中x的取值可以是0～9，xxx中有1～3位。234         String reg_ipv4 = "[0-9]{3}(\\.[0-9]{1,3}){3}";    235 236         String ipv4addr1 = "192.168.1.102";237         String ipv4addr2 = "192.168";238         System.out.printf("%-40s = %b\n", "ipv4addr1.matches()", ipv4addr1.matches(reg_ipv4));239         System.out.printf("%-40s = %b\n", "ipv4addr2.matches()", ipv4addr2.matches(reg_ipv4));240 241         System.out.println();242     }243 244     /**245      * String 的valueOf()演示程序246      */247     private static void testValueAPIs() {248         System.out.println("-------------------------------- testValueAPIs --------------------------------");249         // 1. String    valueOf(Object obj)250         //  实际上，返回的是obj.toString();251         HashMap map = new HashMap();252         map.put("1", "one");253         map.put("2", "two");254         map.put("3", "three");255         System.out.printf("%-50s = %s\n", "String.valueOf(map)", String.valueOf(map));256 257         // 2.String    valueOf(boolean b)258         System.out.printf("%-50s = %s\n", "String.valueOf(true)", String.valueOf(true));259 260         // 3.String    valueOf(char c)261         System.out.printf("%-50s = %s\n", "String.valueOf('m')", String.valueOf('m'));262 263         // 4.String    valueOf(int i)264         System.out.printf("%-50s = %s\n", "String.valueOf(96)", String.valueOf(96));265 266         // 5.String    valueOf(long l)267         System.out.printf("%-50s = %s\n", "String.valueOf(12345L)", String.valueOf(12345L));268 269         // 6.String    valueOf(float f)270         System.out.printf("%-50s = %s\n", "String.valueOf(1.414f)", String.valueOf(1.414f));271 272         // 7.String    valueOf(double d)273         System.out.printf("%-50s = %s\n", "String.valueOf(3.14159d)", String.valueOf(3.14159d));274 275         // 8.String    valueOf(char[] data)276         System.out.printf("%-50s = %s\n", "String.valueOf(new char[]{'s','k','y'})", String.valueOf(new char[]{'s','k','y'}));277 278         // 9.String    valueOf(char[] data, int offset, int count)279         System.out.printf("%-50s = %s\n", "String.valueOf(new char[]{'s','k','y'}, 0, 2)", String.valueOf(new char[]{'s','k','y'}, 0, 2));280 281         System.out.println();282     }283 284     /**285      * String 中index相关API演示286      */287     private static void testIndexAPIs() {288         System.out.println("-------------------------------- testIndexAPIs --------------------------------");289 290         String istr = "abcAbcABCabCaBcAbCaBCabc";291         System.out.printf("istr=%s\n", istr);292 293         // 1. 从前往后，找出‘a’第一次出现的位置294         System.out.printf("%-30s = %d\n", "istr.indexOf((int)'a')", istr.indexOf((int)'a'));295 296         // 2. 从位置5开始，从前往后，找出‘a’第一次出现的位置297         System.out.printf("%-30s = %d\n", "istr.indexOf((int)'a', 5)", istr.indexOf((int)'a', 5));298 299         // 3. 从后往前，找出‘a’第一次出现的位置300         System.out.printf("%-30s = %d\n", "istr.lastIndexOf((int)'a')", istr.lastIndexOf((int)'a'));301 302         // 4. 从位置10开始，从后往前，找出‘a’第一次出现的位置303         System.out.printf("%-30s = %d\n", "istr.lastIndexOf((int)'a', 10)", istr.lastIndexOf((int)'a', 10));304 305 306         // 5. 从前往后，找出"bc"第一次出现的位置307         System.out.printf("%-30s = %d\n", "istr.indexOf(\"bc\")", istr.indexOf("bc"));308 309         // 6. 从位置5开始，从前往后，找出"bc"第一次出现的位置310         System.out.printf("%-30s = %d\n", "istr.indexOf(\"bc\", 5)", istr.indexOf("bc", 5));311 312         // 7. 从后往前，找出"bc"第一次出现的位置313         System.out.printf("%-30s = %d\n", "istr.lastIndexOf(\"bc\")", istr.lastIndexOf("bc"));314 315         // 8. 从位置4开始，从后往前，找出"bc"第一次出现的位置316         System.out.printf("%-30s = %d\n", "istr.lastIndexOf(\"bc\", 4)", istr.lastIndexOf("bc", 4));317 318         System.out.println();319     }320 321     /**322      * String 中与unicode相关的API323      */324     private static void testUnicodeAPIs() {325         System.out.println("-------------------------------- testUnicodeAPIs ------------------------------");326 327         String ustr = new String(new int[] {0x5b57, 0x7b26, 0x7f16, 0x7801}, 0, 4);  // "字符编码"(\u5b57是‘字’的unicode编码)。0表示起始位置，4表示长度。328         System.out.printf("ustr=%s\n", ustr);329 330         //  获取位置0的元素对应的unciode编码331         System.out.printf("%-30s = 0x%x\n", "ustr.codePointAt(0)", ustr.codePointAt(0));332 333         // 获取位置2之前的元素对应的unciode编码334         System.out.printf("%-30s = 0x%x\n", "ustr.codePointBefore(2)", ustr.codePointBefore(2));335 336         // 获取位置1开始的元素对应的unciode编码337         System.out.printf("%-30s = %d\n", "ustr.offsetByCodePoints(1, 2)", ustr.offsetByCodePoints(1, 2));338 339         // 获取第0~3个元素之间的unciode编码的个数340         System.out.printf("%-30s = %d\n", "ustr.codePointCount(0, 3)", ustr.codePointCount(0, 3));341 342         System.out.println();343     }344 }

by：
http://www.cnblogs.com/skywang12345/p/string01.html
http://www.cnblogs.com/skywang12345/p/string02.html
http://www.cnblogs.com/skywang12345/p/string03.html