String
初稿：2017-11-19 23:57:11
String的构造方法
1 import java.nio.charset.Charset; 2 import java.io.UnsupportedEncodingException; 3 4 public class StringContructorTest { 5 6 public static void main(String[] args) { 7 testStringConstructors() ; 8 } 9 private static void testStringConstructors() { 10 try { 11 System.out.println("------------------------ testStringConstructors -----------------------"); 12 13 String str01 = new String(); 14 String str02 = new String("String02"); 15 String str03 = new String(new char[]{'s','t','r','0','3'}); 16 String str04 = new String(new char[]{'s','t','r','0','4'}, 1, 3); 17 String str05 = new String(new StringBuffer("StringBuffer")); 18 String str06 = new String(new StringBuilder("StringBuilder")); 19 String str07 = new String(new byte[]{0x61, 0x62, 0x63, 0x64, 0x65}); 20 // 0x61在ASC表中，对应字符"a"; 1表示起始位置，3表示长度 21 String str08 = new String(new byte[]{0x61, 0x62, 0x63, 0x64, 0x65}, 1, 3); 22 // 0x61在ASC表中，对应字符"a"; 1表示起始位置，3表示长度 23 String str09 = new String(new byte[]{(byte)0xe5, (byte)0xad, (byte)0x97, 24 (byte)0xe7, (byte)0xac, (byte)0xa6, 25 (byte)0xe7, (byte)0xbc, (byte)0x96, 26 (byte)0xe7, (byte)0xa0, (byte)0x81}, 27 0, 12, "utf-8"); // 0表示起始位置，12表示长度。 28 String str10 = new String(new byte[]{(byte)0x5b, (byte)0x57, 29 (byte)0x7b, (byte)0x26, 30 (byte)0x7f, (byte)0x16, 31 (byte)0x78, (byte)0x01}, 32 0, 8, "utf-16"); // 0表示起始位置，8表示长度。 33 String str11 = new String(new byte[]{(byte)0xd7, (byte)0xd6, 34 (byte)0xb7, (byte)0xfb, 35 (byte)0xb1, (byte)0xe0, 36 (byte)0xc2, (byte)0xeb}, 37 Charset.forName("gb2312")); 38 String str12 = new String(new byte[]{(byte)0xd7, (byte)0xd6, 39 (byte)0xb7, (byte)0xfb, 40 (byte)0xb1, (byte)0xe0, 41 (byte)0xc2, (byte)0xeb}, 42 0, 8, Charset.forName("gbk")); 43 String str13 = new String(new int[] {0x5b57, 0x7b26, 0x7f16, 0x7801},0,4); 44 //"字符编码"(\u5b57是‘字’的unicode编码)。0表示起始位置，4表示长度。 45 System.out.println("str01 = " + str01); 46 System.out.println("str02 = " + str02); 47 System.out.println("str03 = " + str03); 48 System.out.println("str04 = " + str04); 49 System.out.println("str05 = " + str05); 50 System.out.println("str06 = " + str06); 51 System.out.println("str07 = " + str07); 52 System.out.println("str08 = " + str08); 53 System.out.println("str09 = " + str09); 54 System.out.println("str10 = " + str10); 55 System.out.println("str11 = " + str11); 56 System.out.println("str12 = " + str12); 57 System.out.println("str13 = " + str13); 58 } catch (UnsupportedEncodingException e) { 59 e.printStackTrace(); 60 } 61 } 62 }
String的常用方法
int compareTo(String str) 如果equals，返回0，如果出现字符不匹配，返回Unicode码值差，如果满足子串关系，返回方法串.len - 参数串.len
int compareToIgnoreCase(String str) 同上，但不区分大小写
boolean equals(String str) 如果完全相同，返回true，否则返回false
boolean equalsIgnoreCase(String str) 同上，但是不区分大小写
boolean startsWith(String str) 是不是以str开头
boolean endsWith(String str) 是不是以str结尾
boolean contains(String str)是不是包含子串str
String toUpperCase() 转成大写
String toLowerCase() 转成小写
boolean contentEquals(StringBuffer str)
boolean contentEquals(StringBuilder str)
String concat(String str) 调用串后接参数串并返回
String substring(int startindex, int endindex) 截取一个子串
String replace('单个字符' ， '单个字符') 把所有的某个特定字符转换成另外一个字符并返回
String replace("单个字符或字符串"，“单个字符或字符串”) 替换 并返回
String[ ] split("字符串") 将字符串以某个字符串作为分界线，拆分成多个子字符串并返回字符串数组
1. 字符串长度
int = str.length()
2. 字符串是否为空
boolean str.isEmpty()
3. [字节] 获取字符串对应的字节数组
byte[] barr = str.getBytes()
4. [字符] 获取字符串位置4的字符
char str.charAt(4)
5.[字符] 获取字符串对应的字符数组 char[] carr = str.toCharArray();
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1 -------------------------------- testIndexAPIs -------------------------------- 2 istr=abcAbcABCabCaBcAbCaBCabc 3 istr.indexOf((int)'a') = 0 4 istr.indexOf((int)'a', 5) = 9 5 istr.lastIndexOf((int)'a') = 21 6 istr.lastIndexOf((int)'a', 10) = 9 7 istr.indexOf("bc") = 1 8 istr.indexOf("bc", 5) = 22 9 istr.lastIndexOf("bc") = 22 10 istr.lastIndexOf("bc", 4) = 4 11 12 13 -------------------------------- testCompareAPIs ------------------------------ 14 str=abcAbcABCabCAbCabc 15 str.equals("abcAbcABCabCAbCabc") = true 16 str.equalsIgnoreCase("ABCABCABCABCABCABC") = true 17 str.compareTo("abce") = -36 18 str.compareToIgnoreCase("ABC") = 15 19 str.startsWith("ab") = true 20 str.startsWith("Ab") = true 21 str.endsWith("bc") = true 22 str.contains("ABC") = true 23 regionMatches(cAbcABCabCAbCabc) = true 24 regionMatches(CABCABCABCABCABC) = false 25 regionMatches(cabcabcabcabcabc) = false 26 str.contentEquals(new StringBuffer("abcAbcABCabCAbCabc")) = true 27 str.contentEquals(new StringBuilder("abcAbcABCabCAbCabc")) = true 28 ipv4addr1.matches() = true 29 ipv4addr2.matches() = false 30 31 32 -------------------------------- testModifyAPIs ------------------------------- 33 str= abcAbcABCabCAbCabc , len=20 34 str.concat("123") = abcAbcABCabCAbCabc 123 35 str.substring(7) = ABCabCAbCabc 36 str.substring(7, 10) = ABC 37 str.trim() = abcAbcABCabCAbCabc, len=18 38 str.replace('a', 'M') = _bcAbcABC_bCAbC_bc 39 str.replaceFirst("a", "###") = ###bcAbcABCabCAbCabc 40 str.replace("a", "$$$") = $$$bcAbcABC$$$bCAbC$$$bc 41 splits[0]= a 42 splits[1]=cA 43 splits[2]=cABCa 44 splits[3]=CA 45 splits[4]=Ca 46 splits[5]=c 47 48 -------------------------------- testUnicodeAPIs ------------------------------ 49 ustr=字符编码 50 ustr.codePointAt(0) = 0x5b57 51 ustr.codePointBefore(2) = 0x7b26 52 ustr.offsetByCodePoints(1, 2) = 3 53 ustr.codePointCount(0, 3) = 3 54 55 -------------------------------- testOtherAPIs -------------------------------- 56 str=0123456789 57 str.length() = 10 58 str.isEmpty() = false 59 barr[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 60 str.charAt(4) = 4 61 carr[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 62 carr2[0]=6 carr2[1]=7 carr2[2]=8 63 str.copyValueOf(new char[]{'a','b','c','d','e'}) = abcde 64 str.copyValueOf(new char[]{'a','b','c','d','e'}, 1, 4) = bcde 65 str.format() = abc-3-true
String将各种对象转换成String的API
1 import java.util.HashMap; 2 public class StringValueTest { 3 public static void main(String[] args) { 4 testValueAPIs() ; 5 } 6 private static void testValueAPIs() { 7 System.out.println("-------------------------------- testValueAPIs --------------------------------"); 8 // 1. String valueOf(Object obj) 9 // 实际上，返回的是obj.toString(); 10 HashMap map = new HashMap(); 11 map.put("1", "one"); 12 map.put("2", "two"); 13 map.put("3", "three"); 14 System.out.println("String.valueOf(map) "+String.valueOf(map)); 15 // 2.String valueOf(boolean b) 16 System.out.println("String.valueOf(true) "+String.valueOf(true)); 17 // 3.String valueOf(char c) 18 System.out.println("String.valueOf('m') "+String.valueOf('m')); 19 // 4.String valueOf(int i) 20 System.out.println("String.valueOf(96) "+String.valueOf(96)); 21 // 5.String valueOf(long l) 22 System.out.println("String.valueOf(12345L) "+String.valueOf(12345L)); 23 // 6.String valueOf(float f) 24 System.out.println("String.valueOf(1.414f) "+String.valueOf(1.414f)); 25 // 7.String valueOf(double d) 26 System.out.println("String.valueOf(3.14159d) "+String.valueOf(3.14159d)); 27 // 8.String valueOf(char[] data) 28 System.out.println("String.valueOf(new char[]{'s','k','y'}) "+String.valueOf(new char[]{'s','k','y'})); 29 // 9.String valueOf(char[] data, int offset, int count) 30 System.out.println("String.valueOf(new char[]{'s','k','y'}, 0, 2) "+String.valueOf(new char[]{'s','k','y'}, 0, 2)); 31 } 32 }
String查找特定字符或字符串的API
1 String istr = new String("abcAbcABCabCaBcAbCaBCabc")； 2 istr.indexOf((int)'a') = 0//从前往后，找出‘a’第一次出现的位置 3 istr.indexOf((int)'a', 5) = 9//从位置5开始，从前往后，找出‘a’第一次出现的位置 4 istr.lastIndexOf((int)'a') = 21//从后往前，找出‘a’第一次出现的位置 5 istr.lastIndexOf((int)'a', 10) = 9//从位置10开始，从后往前，找出‘a’第一次出现的位置 6 istr.indexOf("bc") = 1//从前往后，找出"bc"第一次出现的位置 7 istr.indexOf("bc", 5) = 22//从位置5开始，从前往后，找出"bc"第一次出现的位置 8 istr.lastIndexOf("bc") = 22//从后往前，找出"bc"第一次出现的位置 9 istr.lastIndexOf("bc", 4) = 4//从位置4开始，从后往前，找出"bc"第一次出现的位置
