Java第二章补充-字符串课件

单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,整理课件,*,I Constructing a String,Chapter 2 The String Class,II String Methods,1,整理课件,The,String,Class,Constructing a String:,Obtaining String length and Retrieving Individual Characters in a string String,String Concatenation(,concat,),Substrings(substring(index),substring(start,end),Comparisons(equals,compareTo),String Conversions,Finding a Character or a Substring in a String,Conversions between Strings and Arrays,Converting Characters and Numeric Values to Strings,2,整理课件,Constructing Strings,Format:String,newString,=new,String(stringLiteral,);,String message=“,stringLiteral,;,Example:String message=new String(“Hello);,String message=Welcome to Java;,3,整理课件,Storage,String pool&stack&heap,String pool,（,字符串池,）,:JVM has a String pool,it saves a lot of String objects that created by shorthand,initializer,.Data sharing,Stack,（栈）,:Store primitive data,（,char,、,byte,、,short,、,int,、,long,、,float,、,double,、,boolean,）,and constructor.Data sharing.,heap,（堆）,：,Store Object.,4,整理课件,String,str,=new,String(abc,);,Difference between new and shorthand initializer,Question:How many String objects are created?,Two,Constructor:,publicString(Stringoriginal),/othercode.,Note:The parameter is a String object,5,整理课件,Stringa=,abc,;,String b=,abc,;,Difference between new and shorthand initializer,Question:How many String objects are created?,One,6,整理课件,A new object is created if you use the new operator.,If you use the string initializer,no new object is created if the interned object is already created.,Note,7,整理课件,Strings Are Immutable,A String object is immutable;its contents cannot be changed.,Does the following code change the contents of the string,String s=Java;,s=HTML;,？,8,整理课件,s:String,String object for“Java”,0 x1245,s,Trace Code,String s=Java;,s=HTML;,Contents can not be changed,After executing s=“java”;,s:String,String object for“Java”,0 x1245,s,After executing s=“HTML”;,s:String,String object for“HTML”,9,整理课件,Canonical Strings（规范字符串）,canonical string:,if two String objects were created with,the same string literal,using the,shorthand initializer,then the JVM stores them in the same object.This string literal is called,canonical string,.,improve efficiency and save memory,U,sing,String,objects,intern,method to return a canonical string,10,整理课件,intern:,public native,String,intern(),Returns a canonical representation for the string object.,If s and t are strings such that s.equals(t),it is guaranteed that,s.intern()=t.intern().,Canonical Strings,11,整理课件,String s=Welcome to Java;,String s1=new String(Welcome to Java);,String s2=s1.intern();,String s3=Welcome to Java;,System.out.println(s1=s is +(s1=s);,System.out.println(s2=s is +(s2=s);,System.out.println(s=s3 is +(s=s3);,:String,Canonical string object for Welcome to Java,:String,A string object for Welcome to Java,Examples,display,s1=s is false,s2=s is true,s=s3 is true,12,整理课件,Finding String Length,Finding string length using the,length(),method:,Example：message=Welcome;,message.length(),(returns 7),13,整理课件,Retrieving Individual Characters in a String,Do not use,message0,Use,message.charAt(index,),public char,charAt(int,index),Returns the character at the specified index.An index ranges from 0 to length()-1.,Index starts from,0,charAt方法的使用,14,整理课件,public String concat(String str),Concatenates the specified string to the end of this string.,If the length of the argument string is 0,then this object is returned.,Parameters:the String that is concatenated to the end of this String.,Returns:a string that represents the concatenation of this objects characters followed by the string arguments characters.,String Concatenation,15,整理课件,String Concatenation,String s3=,s1.concat(s2),;,String s3=s1+s2;,s1+s2+s3+s4+s5 same as,(s1.concat(s2).concat(s3).concat(s4).concat(s5);,16,整理课件,public String substring(int beginIndex),Returns a new string that is a substring of this string.The substring begins at the specified index and extends to the end of this string.,public String substring(int beginIndex,int endIndex),Returns a new string that is a substring of this string.The substring begins at the specified beginIndex and extends to the character at index endIndex-1.,Parameters:the beginning index,inclusive.,Returns:the specified substring.,Throws:StringIndexOutOfBoundsException if the beginIndex is out of range.,Extracting Substrings,17,整理课件,Extracting Substrings,String is an,immutable,class;its valuescannot be changed individually.,String s1=Welcome to Java;,String s2=,s1.substring(0,11),+HTML;,18,整理课件,String Comparisons,equals,String s1=new String(Welcome“);,String s2=“Welcome;,if(s1.equals(s2),/s1 and s2 have the same contents,if(s1=s2),/s1 and s2 have the same reference,19,整理课件,String Comparisons,cont.,compareTo(Object object),String s1=new String(Welcome“);,String s2=welcome;,if(pareTo(s2)0),/s1 is greater than s2,else if(pareTo(s2)=0),/s1 and s2 have the same contents,else,/s1 is less than s2,20,整理课件,String Conversions,The contents of a str