slideJava的基础教程好.ppt

1,Objectives,TousetheStringclasstoprocessfixedstringsTousetheCharacterclasstoprocessasinglecharacterTousetheStringBufferclasstoprocessflexiblestringsTolearnhowtopassstringstothemainmethodfromthecommandlineTodiscoverfileproperties,deleteandrenamefilesusingtheFileclassTowritedatatoafileusingthePrintWriterclassToreaddatafromafileusingtheScannerclass,2,Introduction(P2628.1),Stringareusedofteninprogramming.AStringisasequenceofcharacters.Inmanylanguage,stringsaretreatedasarrayofcharacters,butinJavaastringisanObject.,3,StringsAreImmutable(8.2.2),AStringobjectisimmutable;itscontentscannotbechanged.Doesthefollowingcodechangethecontentsofthestring?Strings=Java;s=s+HTML;,4,ConstructaString,(1)Tocreatingastringfromastringliteral(2)Sincestringsareusedfrequently,Javaprovidesashorthandinitializerforcreatingastring:(3)Createastringfromanarrayofcharacters,Stringmessage=newString(WelcometoJava);,Stringmessage=WelcometoJava;,charcharArray=g,o,o,d;Stringmessage=newString(charArray);,5,InternedStrings,Strings1=newString(welcometojava);Strings2=newString(welcometojava);System.out.println(s1=s2);,Strings1=welcometojava;Strings2=welcometojava;System.out.println(s1=s2);,Strings1=welcometojava;Strings2=newString(welcometojava);System.out.println(s1=s2);,6,InternedStrings(8.2.2),Sincestringsareimmutableandarefrequentlyused,toimproveefficiencyandsavememory,theJVMusesauniqueinstanceforstringliteralswiththesamecharactersequence.Suchaninstanceiscalledinterned.YoucanalsouseaStringobjectsinternmethodtoreturnaninternedstring.,7,Examples(8.2.2),Display:s1=sisfalses2=sistrues=s3istrue,Anewobjectiscreatedifyouusethenewoperator.Ifyouusethestringinitializer,nonewobjectiscreatediftheinternedobjectisalreadycreated.,8,FindingStringLength(8.2.4),Definition:publicintlength(),Stringmessage=Welcome;intlength=message.length();/7for(inti=0;imessage.length();i+),9,RetrievingIndividualCharacter(8.2.4),Definition:publiccharcharAt(intindex),Stringmessage=welcometojava;charc1=messsage.charAt(0);/wcharc2=messsage.charAt(message.length()-1);/a,10,Exercise1,输入任意字符串，将其反向输出Scannerinput=newScanner(System.in);Strings=input.next();反向输出s,11,Exercise2(P270listing8.1),判断一个字符串是不是回文（palindrome）Palindrome：dad，mom，noonNotPalindrome：ok，event,12,Exercise3,编写方法count，在字符串中寻找一个字符的出现次数,例如count(“welcome”,e);/returns2publicstaticintcount(Stringstr,charc),13,ObtainingSubstrings(8.2.6),Definition:publicStringsubstring(intbeginIndex)publicStringsubstring(intbeginIndex,intendIndex),Strings1=WelcometoJava;Strings2=s1.substring(0,11);/(0-includsive,11-excludsive)Strings3=s1.substring(11);/11-includsive,14,FindingaCharacteroraSubstring(8.2.8),publicintindexOf(intch)publicintindexOf(Strings)Returnstheindexofthefirstoccurrenceofthespecifiedcharacter/string-1ifthecharacterdoesnotoccurpublicintlastIndexOf(intch)publicintlastIndexOf(Stringch)Returnstheindexofthelastoccurrenceofthespecifiedcharacter-1ifthecharacterdoesnotoccur,15,Example,Stringmessage=“WelcometoJava”;intindex=message.indexOf(a);/12.index=message.indexOf(x);/-1.index=message.indexOf(“java”);/-1.index=message.indexOf(“Java”);/11.index=message.lastIndexOf(“va”);/13.,16,FindingaCharacteroraSubstring(8.2.8),publicintindexOf(intch,intfromIndex)publicintindexOf(Strings,intfromIndex)Returnstheindexstringofthefirstoccurrenceofthespecifiedcharacter/string,startingthesearchatthespecifiedindex.-1ifthecharacterdoesnotoccurpublicintlastIndexOf(intch,intfromIndex)publicintlastIndexOf(Stringstr,intfromIndex)Returnstheindexwithinthisstringofthelastoccurrenceofthespecifiedsubstring,searchingbackwardstartingatthespecifiedindex.-1ifthecharacterdoesnotoccur,17,Example,Stringmessage=“WelcometoJava”;intindex=message.indexOf(a,13);/14.index=message.indexOf(“We,5);/returns-1.index=message.indexOf(o,2);/?index=message.indexOf(o,6);/?,18,Exercise4,编写程序，输出任意double数的整数部分几位，小数部分几位？例如：123456.69，整数部分6位，小数部分2位Scannerinput=newScanner(System.in);doublenum=input.nextDouble();提示：1.将num转换为字符串：Stringsnum=num+”;2.找到小数点的位置：intpoint=snum.indexOf(?);3.截取整数部分子串:Stringpart1=snum.subString(?,?);4.截取小数部分子串：Stringpart2=snum.subString(？);5.分别输出整数部分长度和小数部分长度,19,Exercise5,输入任意文件路径，输出其路径、文件名、文件扩展名。例如输入：E:/08-09-2-Java/PPT/chapter8.ppt输出：文件路径：E:/08-09-2-Java/PPT文件名：chapter8文件扩展名：ppt,20,Exercise6,实现indexOf函数publicintindexOf(Strings1,Strings2)在s1中找s2，返回其首次出现的位置，找不到返回-1不使用String类的indexOf!,21,Exercise7,编写函数compare，比较两个字符串从同一位置开始，有多少个字符连续相同，返回最大的相同数。例如：“6220462”“9020466”，4个“622046212121”“902046612121”，5个staticintcompare(Strings1,Strings2),22,StringComparisons(8.2.3),publicbooleanequals(Objecto),Scannerinput=newScanner(System.in);Strings1=input.next();Strings2=input.next();if(s1.equals(s2)System.out.println(“两个字符串包含的字符相同”);,23,思考题,classCircledoubleradius;Circle(doublenewRadius)radius=newRadius;测试：Circlec1=newCircle(5.5);Circlec2=newCircle(5.5);System.out.println(c1.equals(c2);/false,24,publicbooleanequals(ObjectanObject)if(this=anObject)returntrue;if(anObjectinstanceofString)StringanotherString=(String)anObject;intn=count;if(n=anotherString.count)charv1=value;charv2=anotherString.value;inti=offset;intj=anotherString.offset;while(n-!=0)if(v1i+!=v2j+)returnfalse;returntrue;returnfalse;,equals是Object类中的一个方法（该方法将比较两个对象的地址是否相同），它被java所有的类继承。如果某个类对于equals条件有任何其他要求，则需要改写equals方法，下面是String类的equals方法。仿照该方法为Circle类提供equals方法，当两个圆的半径相同返回true，否则返回false。,25,StringComparisons(8.2.3),publicbooleanstartsWith(Stringprefix)publicbooleanendsWith(Stringsuffix),Scannerinput=newScanner(System.in);Strings1=input.next();if(s1.startsWith(“java”)System.out.println(“该字符串由java开头”);if(s1.endsWith(“java”)System.out.println(“该字符串由java结尾”);,26,MatchingString(8.6.1),publicbooleanmatches(Stringregex),Scannerinput=newScanner(System.in);Strings1=input.next();if(s1.matches(“d.*d”)System.out.println(“该字符串由数字开头，数字结尾”);if(s1.matches(“A-Z1,40-92”)System.out.println(“该字符串1-4个A-Z字符开头，以2个数字结尾”);,27,“.”代表任何字符“d”代表任何数字，“D”代表任何非数字字符“s”代表空格，“S”代表任何非空格字符“x*”代表0个或多个x，（xy）*代表0个或多个xy“x?”代表0个或1个x，（xy）?代表0个或1个xy“x+”代表1个或多个x，（xy）+代表1个或多个xyxyz表示取x，y，z其中一个0-9表示取0-9其中一个x|y|z表示取x，y，z其中一个“x5”表示5个x“x5，”表示至少5个x“x5，8”表示至少5个x，最多8个x（xyz）2表示xyz出现两次,28,Exercise8,判断一个字符串是不是java合法标识符，regex代表java合法标识符：字母(pL)，下划线，$开头，后跟字母，下划线，数字pN，$任意组合Scannerinput=newScanner(System.in);Strings=input.next();Stringregex=“(pL|_|$)(pN|pL|_|$)*”;if(s1.matches(regex)System.out.println(“该字符串可以作为Java标识符”);,29,Exercise9,判断输入是不是正确的邮件地址正确地址：字母(包括大小写)数字的任意组合+字母(包括大小写)数字的任意组合+.net或者.com,30,StringConversions(8.2.7),publicStringtoUpperCase()publicStringtoLowerCase()publicStringtrim()publicStringreplace(charoldChar,charnewChar),Scannerinput=newScanner(System.in);Strings=input.next();Stringsu=s.toUpperCase();Stringsl=s.toLowerCase();Stringst=s.trim();Stringsr=s.replace(a,A);,31,Splitstring,Strings=“12,13,15,16,18,19”;StringsArray=s.split(“,”);,sArray,32,ConvertCharacterandNumberstoStrings(8.2.10),StringtonumberStringsdnum=“12.5”;Stringsinum=“50”;doublednum=Double.parseDouble(snum);intinum=Integer.parseInt(sinum);NumbertoStringdoubled=14.8;Stringsnum=d+“”;,33,Exercise10,输入一串用“,”分隔的数字串，求和,34,TheStringBufferClass(P2738.4),TheStringBufferclassisanalternativetotheStringclass.Ingeneral,astringbuffercanbeusedwhereverastringisused.StringBufferismoreflexiblethanString.Youcanadd,insert,orappendnewcontentsintoastringbuffer.,35,StringBufferConstructors,publicStringBuffer()Nocharacters,initialcapacity16characters.publicStringBuffer(intlength)Nocharacters,initialcapacityspecifiedbythelengthargument.publicStringBuffer(Stringstr)Representsthesamesequenceofcharactersasthestringargument.Initialcapacity16plusthelengthofthestringargument.,36,AppendingNewContentsintoaStringBuffer,StringBufferstrBuf=newStringBuffer();strBuf.append(Welcome);strBuf.append();strBuf.append(to);strBuf.append();strBuf.append(Java);,37,insertNewContentsintoaStringBuffer,StringBuffermainStr=newStringBuffer(“黄河远上白云，一片孤城万仞山);StringsubStr=间;mainStr.insert(6,subStr);System.out.println(mainStr);,38,deleteContentsfromaStringBuffer,StringBuffermainStr=newStringBuffer(“黄河远上白云间,一片孤城万仞山);mainStr.deleteCharAt(4);System.out.println(mainStr);StringBuffermainStr2=newStringBuffer(“黄河远上白云间,一片孤城万仞山);mainStr2.delete(0,8);System.out.println(mainStr2);/一片孤城万仞山,39,modifyStringBuffer,StringBuffermodiStr=newStringBuffer(Wheniamyoung,Idlisteningtotheradio);modiStr.setCharAt(5,I);modiStr.replace(7,9,was);System.out.println(modiStr);,40,Exercise15,从输入的字符串中删除指定的字符串，例如：输入“thisisastring”,删除“is”，删除后的串为”thastring”staticStringdelete(Strings,Stringdel),41,Exercise16,将一个十进制的字符串转换为逗号分隔的字符串，从右边开始每三个数字标一个逗号。例如1234567，返回1,234,567staticStringinsert(Stringnum,intinterval),42,TheCharacterClass,43,Example,charc=f;if(Character.isDigit(c)System.out.println(c+是数字);elseif(Character.isLetter(c)System.out.println(c+“是字母);,44,Example,charc=f;if(Character.isUpperCase(c)System.out.println(c+是大写);elseif(Character.isLowerCase(c)System.out.println(c+是小写);elseSystem.out.println(c+不分大小写);,45,Example,charc=f;if(Character.isUpperCase(c)System.out.println(Character.toLowerCase(c);elseif(Character.isLowerCase(c)System.out.println(Character.toUpperCase(c);elseSystem.out.println(c+不分大小写);,46,Example,charc=1;if(Character.isDigit(c)intnum=Character.getNumericValue(c);num+;System.out.println(num);elseSystem.out.println(c+不是数字);,47,Exercise11,统计一个字符串中有多少个数字,例如：”cat223dog456n”中数字个数是6publicstaticintcount(Strings),48,Exercise12,二进制转化为10进制publicstaticintparseBinary(StringbinaryString)intnum=parseBinary(“1001”)：1*23+0*22+0*21+1*20=9；,49,Exercise13,统计一个字符串中每个数字出现多少次publicstaticintcount(Strings)intcount=newint10;提示：用counti存储i的个数例如：intcount=count(“12203AB3”);输出：0出现1次1出现1次2出现2次3出现2次4出现0次,50,Exercise14,统计字符串中有多少个数字段例如：“cat223dog456nice25ttt98”数字段个数是4publicstaticintcount(Strings),51,TheFileClass,TheFileclassisawrapperclassforthefilenameanditsdirectorypath.,52,53,importjava.io.*;publicclassTestFileClasspublicstaticvoidmain(Stringargs)Filefile=newFile(“d:/image/us.gif);System.out.println(Doesitexist?+file.exists();System.out.println(Canitberead?+file.canRead();System.out.println(Canitbewritten?+file.canWrite();System.out.println(Isitadirectory?+file.isDirectory();System.out.println(Isitafile?+file.isFile();System.out.println(Isitabsolute?+file.isAbsolute();System.out.println(Isithidden?+file.isHidden();System.out.println(Absolutepathis+file.getAbsolutePath();System.out.println(Lastmodifiedon+newjava.util.Date(file.lastModified();,54,CreateFile,Filef1=newFile(“D:/test/a.doc”);/创建指定文件booleanb=f1.createNewFile();Filef2=newFile(D:test1test2);/创建指定文件夹，如果上层文件夹不存在，会一同创建booleanb=f2.mkdirs();/只创建最后一层文件夹，如果上层文件夹不存在，创建失败b=f2.mkdir();/,55,Deletefile,Filef1=newFile(“D:/test/a.doc”);f1.delete();/删除文件Filef2=newFile(D:/test);f2.delete();/删除文件夹，文件夹必须为空才能删除,56,Renamefile,将D:/test/a.doc重命名成b.docFilef1=newFile(D:/test/a.doc);Filef2=newFile(D:/test/b.doc);f1.renameTo(f2);将D:/test/a.doc转移到D:/Filef1=newFile(D:/test/a.doc);Filef2=newFile(D:/a.doc);f1.renameTo(f2);,57,WritingDataUsingPrintWriter,importjava.io.*;publicclassPrintWriterDemopublicstaticvoidmain(Stringargs)throwsFileNotFoundExceptionPrintWriterpw=newPrintWriter(“d:/a.txt”);pw.println(“天天好心情_);pw.print(123456);pw.close();,58,WritingDataUsingPrintWriter,importjava.io.*;Importjava.util.*;publicclassPrintWriterDemopublicstaticvoidmain(Stringargs)throwsFileNotFoundExceptionScannerin=newScanner(System.in);PrintWriterpw=newPrintWriter(d:/a.txt);for(inti=0;i2;i+)System.out.println(请输入学号);Stringid=in.next();pw.print(id+“);System.out.println(请输入姓名);Stringname=in.next();pw.print(name+“);System.out.println(请输入年龄);intage=in.nextInt();pw.println(age);pw.close();,1张三202李四19,59,WritingDataUsingPrintWriter,60,TheScannerClass,JDK1.5Feature,Scannerscanner=newScanner(System.in);Strings=scanner.next();System.out.println(s);,Input:WelcometoJava!Javaisfun!Javaiscool!Output:Welcome,Bydefault,thedelimitersforseparatingtokensinaScannerarewhiteSpaces,61,TheScannerClass,Scannerscanner=newS