我来弄些财富呵呵10.常用类.ppt

Java面向对象程序设计 数组 2 本节内容 字符串操作类java lang String类构造方法java lang StringBuffer类java util StringTokenizer类不同的应用场合 3 String类的构造方法 生成空字符串publicString 从byte数组生成 0 127 publicString byte bytes publicString byte bytes intoffset intlength publicString byte bytes Charsetcharset publicString byte bytes intoffset intlength Charsetcharset publicString byte bytes StringcharsetName ascii utf 8 iso 8859 1 utf 16publicString byte bytes intoffset intlength StringcharsetName String类的构造方法 从char数组生成publicString char value publicString char value intoffset intlength 从int数组生成publicString int codePoints intoffset intcode 1114111从字符串生成publicString Stringoriginal publicString StringBufferbuffer publicString StringBuilderbuilder 5 String类的构造方法 java lang String类 字符串 字符序列构造方法的使用 Stringa abc Stringb newString b abc Stringc newString a Stringd newString abc byte bytes 97 98 99 Stringe newString bytes Stringf newString bytes 0 3 char value a b c Stringg newString value int codePoint 97 98 99 Stringh newString codePoint 0 3 a abc b abc c abc d abc e abc f abc g abc h abc 6 String类的构造方法 java lang String类 字符串 字符序列构造方法的使用 classDemo3 publicstaticvoidmain Stringargs try byte bytes 97 98 99 Stringa newString bytes ascii System out println a a Stringb newString bytes utf 8 System out println b b catch Exceptione System out println e 7 String类的比较方法 publicbooleanequals ObjectanObject 判断是否是同一个对象 是 ture 然后anObject是否为一个字符串对象 否 false 是 判断是否内容相同publicbooleanequalsIgnoreCase StringanotherString 判断逻辑与equals相同 仅仅在判断内容上不考虑大小写publicintcompareTo Objecto 若o不是字符串对象 则抛错 若是则调用下面的函数publicintcompareTo StringanotherString 判断两个字符串的内容是否相同 是 0 否 不等于0的整数publicintcompareToIgnoreCase Stringstr 基本功能同上 仅仅在判断时不考虑大小写 classDemo4 publicstaticvoidmain Stringargs Stringa abc Stringb abc Stringc ABC System out println a equals b a equals b System out println a equals c a equals c System out println a equalsIgnoreCase c a equals c System out println pareTo b pareTo b System out println pareTo c pareTo c System out println pareToIgnoreCase c pareTo c 运行结果 a equals b true a equals c false a equalsIgnoreCase c pareTo b pareTo c pareToIgnoreCase c 0 8 String类的取字符或子串方法 获取长度publicintlength 字符串的长度 即包含多少个字符获取特定子串 substring 和字符publicStringsubstring intbeginIndex publicStringsubstring intbeginIndex intendIndex beginIndex 起始索引位置 包含 endIndex 结束索引位置 不包含 publiccharcharAt intindex Strings1 java语言 Strings2 JavA语言 System out println s1 length System out println s2 length System out println s1 substring 0 4 System out println s1 substring 4 System out println s2 substring 0 4 System out println s2 substring 4 System out println s1 charAt 0 运行结果 66java语言JavA语言j 9 字符串操作类 java lang String类 字符串 字符序列字符串前缀 prefix 后缀 suffix 的判断publicbooleanstartsWith Stringprefix 判断字符串是否以一特定的字符串开头publicbooleanstartsWith Stringprefix inttoffset publicbooleanendsWith Stringsuffix 判断字符串是否以一特定的字符串结束 classDemo5 publicstaticvoidmain Stringargs Stringa abc System out println a startsWith ab a startsWith ab System out println a startsWith bc 1 a startsWith bc 1 System out println a endsWith e a endsWith c a startsWith ab true a startsWith b 1 true a endsWith e true 10 String类查询字符 字符串 publicintindexOf intch 该字符在字符串中第一次出现位置的索引值 否则返回 1publicintindexOf intch intfromIndex publicintindexOf Stringstr publicintindexOf Stringstr intfromIndex publicintlastIndexOf intch publicintlastIndexOf intch intfromIndex publicintlastIndexOf Stringstr publicintlastIndexOf Stringstr intfromIndex 11 字符串操作类 java lang String类 字符串 字符序列方法举例 Strings java语言 System out println s indexOf a System out println s indexOf a 2 System out println s indexOf a System out println s indexOf 语言 System out println s lastIndexOf a System out println s lastIndexOf v 1 System out println s lastIndexOf 语言 System out println s lastIndexOf v 2 运行结果 13143 142 12 字符串操作类 java lang String类 字符串 字符序列字符串转变为数组publicbyte getBytes 将字符串转变为一个字节数组publicbyte getBytes StringcharsetName throwsUnsupportedEncodingException按特定的字符编码格式将字符串转变为一个字节数组publicchar toCharArray 将字符串转变为一个字符数组 13 字符串操作类 java lang String类 字符串 字符序列方法举例 Strings java语言 char c s toCharArray System out println c length byte b s getBytes System out println b length b s getBytes ISO8859 1 System out println b length 运行结果 686 中文Windows操作系统 默认字符集GB2312其他系统 默认字符集ISO 8859 1 14 String类的其他方法 publicStringconcat Stringstr 连接字符串 cares concat s returns caress to concat get concat her returns together publicStringreplace charoldChar charnewChar 在字符串中进行字符替换 mesquiteinyourcellar replace e o returns mosquitoinyourcollar JonL replace q x returns JonL nochange String类的基本数据转换方法 staticStringvalueOf booleanb staticStringvalueOf charc staticStringvalueOf char data staticStringvalueOf char data intoffset intcount staticStringvalueOf doubled staticStringvalueOf floatf staticStringvalueOf inti staticStringvalueOf longl staticStringvalueOf Objectobj classDemo6 publicstaticvoidmain Stringargs booleanbo true charc a char chars a b c byteb 1 inti 123456 longl 1234567890l floatf 0 123f doubled 0 456 System out println valueOf boolean String valueOf bo System out println valueOf char String valueOf c System out println valueOf chars String valueOf chars System out println valueOf chars 0 2 String valueOf chars 0 2 System out println valueOf byte String valueOf b System out println valueOf int String valueOf i System out println valueOf long String valueOf l System out println valueOf float String valueOf f System out println valueOf double String valueOf d valueOf boolean true valueOf char a valueOf chars abc valueOf chars 0 2 ab valueOf byte 1 valueOf int 123456 valueOf long 1234567890 valueOf float 0 123 valueOf double 0 456 16 字符串操作类 java lang StringBuffer类一个可变 mutable 动态的字符序列构造方法publicStringBuffer publicStringBuffer Stringstr 主要方法添加 append 和插入 insert 指定位置 publicStringBufferappend booleanb publicStringBufferinsert intoffset booleanb boolean char char double float int long String转换为字符串 publicStringtoString 17 字符串操作类 java lang StringBuffer类 方法举例 Strings java语言 StringBufferbuffer newStringBuffer s buffer append easy buffer insert 6 is buffe append true buffe append 2 s buffer toString System out println s 运行结果 java语言iseasytrue2 18 字符串操作类 字符串的连接运算 Concatenation java 和 语言 Strings java 语言 Strings java concat 语言 StringBufferbuffer newStringBuffer java buffer append 语言 Strings buffer toString 常用第1种和第3种方法 19 字符串操作类 字符串的连接运算 Concatenation 与append方法比较 classMyTimer privatefinallongstart publicMyTimer start System currentTimeMillis publiclonggetElapsed returnSystem currentTimeMillis start publicclassAppDemo staticfinalintN 47500 publicstaticvoidmain Stringargs MyTimermt newMyTimer Stringstr1 for inti 1 i N i str1 str1 System out println 1 stime mt getElapsed mt newMy