Chapter9Strings and Text I/O1.s1==s2=>trues2==s3=>falses1.equals(s2)=>trues2.equals(s3)=>truepareTo(s2)=>0pareTo(s3)=>0s1==s4=>trues1.charAt(0)=>Ws1.indexOf('j')=>-1s1.indexOf("to")=>8stIndexOf('a')=>14stIndexOf("o",15)=>9s1.length()=>16s1.substring(5)=>me to Javas1.substring(5,11)=>me tos1.startsWith("Wel")=>trues1.endsWith("Java")=>trues1.toLowerCase()=>welcome to javas1.toUpperCase()=>WELCOME TO JAVA"Welcome".trim()=>Welcomes1.replace('o','T')=>WelcTme tT Javas1.replaceAll("o","T")=>WelcTme tT Javas1.replaceFirst("o","T")=>WelcTme tT Javas1.toCharArray()returns an array of characters consisting of W,e,l,c,o,m,e,,t,o,,J,a,v,a (Note that none of the operation causes the contents of a string to change)2.String s=new String("new string");Answer:CorrectString s3=s1+s2;Answer:CorrectString s3=s1-s2;Answer:Incorrects1==s2Answer:Corrects1>=s2Answer:IncorrectpareTo(s2);Answer:Correctint i=s1.length();Answer:Correctchar c=s1(0);Answer:Incorrectchar c=s1.charAt(s1.length());Answer:Incorrect:it's out of bounds,even if the preceding problem is fixed.3.The output isWelcome to JavaWelcabcme tabc JavaHint:No method in the String class can change the content of the string.String is an immutable class.4.∙Check whether s1is equal to s2and assign the result to a Boolean variable isEqual.boolean isEqual=s1.equals(s2);∙Check whether s1is equal to s2ignoring case and assign the result to a Boolean variable isEqual.boolean isEqual=s1.equalsIgnoreCase(s2);∙Compare s1with s2and assign the result to an int variable x.int x=pareTo(s2);∙Compare s1with s2ignoring case and assign the result to an int variable x.int x=pareToIgnoreCase(s2);∙Check whether s1has prefix"AAA"and assign the result to a Boolean variable b.boolean b=s1.startsWith("AAA");∙Check whether s1has suffix"AAA"and assign the result to a Boolean variable b.boolean b=s1.endsWith("AAA");∙Assign the length of s1to an int variable x.int x=s1.length();∙Assign the first character of s1to a char variable x. char x=s1.charAt(0);∙Create a new string s3that combines s1with s2.String s3=s1+s2;∙Create a substring of s1starting from index 1.String s3=s1.substring(1);∙Create a substring of s1from index1to index 4. String s3=s1.substring(1,5);∙Create a new string s3that converts s1to lowercase. String s3=s1.lowercase();∙Create a new string s3that converts s1to uppercase. String s3=s1.uppercase();∙Create a new string s3that trims blank spaces on both ends of s1.String s3=s1.trim();∙Replace all occurrence of character e with E in s1and assign the new string to s3.String s3=s1.replaceAll(‘e’,‘E’);∙Split"Welcome to Java and HTML"into an array tokens using delimited by a space.String[]tokens="Welcome to Java and HTML".split(‘‘);∙Assign the index of the first occurrence of charactere in s1to an int variable x.int x=s1.indexOf(‘e‘);Assign the index of the last occurrence of string abc in s1to an int variable x.int x=stIndexOf(“abc”);5.No.6.0.e the overloaded static valueOf method in the String class.8.The text is declared in Line2as a data field,but redeclared in Line5as a localvariable.The local variable is assigned with the string passed to the constructor,but the data field is still null.In Line10,test.text is null,which causesNullPointerException when invoking the toLowerCase()method.9.The constructor is declared incorrectly.It should not have void.10.A lowercase letter is between‘a’and‘z’.You can use the staticisLowerCase(char)method in the Character class to test if a character is inlowercase.An uppercase letter is between‘A’and‘Z’.You can use the staticisUpperCase(char)method in the Character class to test if a character is inuppercase.11.An alphanumeric character is between‘0’and‘9’,or‘A’and‘Z’,or‘a’and‘z’.You can use the static isLetterOrDigit(char ch)method in the Character class totest if a character is a digit or a letter.12.The StringBuilder class,introduced in JDK1.5,is similar to StringBuffer exceptthat the update methods in StringBuffer are synchronized.e the StringBuilder’s constructor to create a string buffer for a string,and usethe toString method in StringBuilder class to return a string from a StringBuilder.14.StringBuilder sb=new StringBuilder(s);sb.reverse();s=sb.toString();15.StringBuilder sb=new StringBuilder(s);sb.delete(4,10);s=sb.toString();16.Both string and string buffer use arrays to hold characters.The array in a string isfixed once a string is created.The array in a string buffer may change if the buffer capacity is changed.To accommodate the change,a new array is created.17.(1)Java is fun(2)JavaHTML(3)Jais funva(4)JHTMLava(5)v(6)4(7)Jav(8)Ja(9)avaJ(10)JComputera(11)av(12)va18.The output isJavaJava and HTMLNOTE:Inside the method,the statement s=s+"and HTML"creates a new String objects,which is different from the original String object passed to the change(s,buffer)method.The original String object has not been changed.Therefore,the printoutfrom the original string is Java.Inside the method,the content of the StringBuilder object is changed to Java andHTML.Therefore,the printout from buffer is Java and HTML.19.public static void main(String[]args)can be replaced bypublic static void main(String args[])public static void main(String[]x)public static void main(String x[])but notstatic void main(String x[])because it is not public.20.(1)Number of strings is4Ihaveadream(2)Number of strings is1123(3)Number of strings is0(4)Number of strings is1*(5)Number of strings is(the number of files and directory from where the commandis executed)Displays all files and directory names in the directory where the command isexecuted.21.The\is a special character.It should be written as\\in Java using the Escapesequence.e exists()in the File class to check whether a file e delete()in the Fileclass to delete this e renameTo(File)to rename the name for this file.Youcannot find the file size using the File class.23.No.The File class can be used to obtain file properties and manipulate files,butcannot perform I/O.24.To create a PrintWriter for a file,use new PrintWriter(filename).This statementmay throw an exception.Java forces you to write the code to deal with exceptions.One way to deal with it is to declare throws Exception in the method declaration.If the close()method is not invoked,the data may not be saved properly.25.The contents of the file temp.txt is:amount is32.320000 3.232000e+01amount is32.3200 3.2320e+01falseJava26.To create a Scanner for a file,use new Scanner(new File(filename)).This statementmay throw an exception.Java forces you to write the code to deal with exceptions.One way to deal with it is to declare throws Exception in the method declaration.If the close()method is not invoked,the problem will run fine.But it is a goodpractice to close the file to release the resource on the file.27.If you attempt to create a Scanner for a nonexistent file,an exception will occur.Ifyou attempt to create a Formatter for an existing file,the contents of the existingfile will be gone.28.No.The line separator on Windows is\r\n.29.intValue contains45.doubleValue contains57.8,andline contains'','7','8','9'.30.intValue contains45.doubleValue contains57.8,andline is empty.。
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