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String Regular Expression Java Core

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Agenda Java String methods String StringBuffer StringBuilder Regular Expression Practical tasks

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Class String As you know we have a number of primitive types in Java which represents next entities: Integer numbers (byte, short, int, long) Real numbers (float, double) Symbols (char) Boolean (boolean) For Strings represents Java doesn’t has a primitive type!!!

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String Strings, which are widely used in Java programming, are a sequence of characters. In the Java programming language, strings are objects. The Java platform provides the String class to create and manipulate strings. Literal automatically creates an object of type String String s1 = "sun.com"; String s2 = new String("sun.com"); String objects are immutable. After creating the content can not be changed. You can always create a new string that contains all changes.

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String String class supports multiple constructors String( ); - String(StringBuffer sbuf); String(String str); - String(StringBuilder sbuild); String(char[ ] unicodechar); ... Just assignee value to variable String strFirst = "First String"; Call constructor of String class String strSecond = new String("Second String"); Call constructor of String class char[] chA = {’A’, ’B’, ’C’, ’D’, ’E’, ’F’}; String strThird = new String(chA); String strFourth = new String(chA, 2, 4); // CDEF

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Basic methods Concat strings String concat(String s) or "+" String str1 = "Hello "; String str2 = "World!"; String str3 = str1 + str2; String str4 = str1.concat(str2); System.out.println(str3 + str4); Get length of string int length() // str3Length = 12 int str3Length = str3.length();

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Basic methods Compare strings boolean equals(Object obj) boolean equalsIgnoreCase(String s) int compareTo(String s) int compareToIgnoreCase(String s) boolean contentEquals(StringBuffer obj)

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Basic methods Get part of string - extract a substring of length m-n, starting at position n String substring(int n, int m) - extract a substring starting at position n String substring(int n) int indexOf(char ch) boolean startsWith(String s) boolean endsWith(String s) char charAt(int position)

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$Basic methods Working with case of symbols String toLowerCase() String toUpperCase() Trim strings String str = "\tTabulated String\t";...$

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Basic methods Working with case of symbols String toLowerCase() String toUpperCase() Trim strings String str = "\tTabulated String\t"; String tStr = str.trim(); Replace symbols String str = "abracadabra"; String rStr = str.replace('a', 'o'); boolean isEmpty()

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Java String methods public static void main(String[] args) { String s1 = "Java"; String s2 = "Java"; String s3 = new String("Java"); System.out.println(s1 + "==" + s2 + " : " + (s1 == s2)); // true System.out.println(s1 + "==" + s3 + " : " + (s1 == s3)); // false System.out.println(s1 + " equals " + s2 + " : " + s1.equals(s2)); // true System.out.println(s1 + " equals " + s3 + " : " + s1.equals(s3)); // true System.out.println(s1.hashCode()); }

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String Constant Pool

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Example public static void main(String[ ] args) { int i; char s[ ] = { 'J', 'a', 'v', 'a' }; String str = new String(s); // str = "Java" if (!str.isEmpty( )) { i = str.length( ); // i = 4 str = str.toUpperCase( ); // str = "JAVA" String num = String.valueOf(8); // num = "8" num = str.concat("-" + num); // num = "JAVA-8" char ch = str.charAt(2); // ch = 'V'

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Example i = str.lastIndexOf('A'); // i = 3 or -1 num = num.replace("8","SE"); // num = "JAVA-SE" str.substring(0, 4).toLowerCase( ); // java str = num + "-8"; // str = "JAVA-SE-8" String[ ] arr = str.split("-"); for (String s : arr) { System.out.println(s); } } }

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String Formatting System.out.printf(“format-string” [, arg1, arg2, … ] ); Format String: % [flags] [width] [.precision] conversion-character Flags: ‘-’ (align), ‘+’ (sign), 0 (forces zero), ‘,’ ‘ ‘ (space) Width - minimum number of characters to be written to the output. Precision - the number of digits of precision when outputting floating-point values or the length of a substring to extract from a String. Conversion-Characters: d : decimal integer [byte, short, int, long] f : floating-point number [float, double] c : character Capital C will uppercase the letter s : String Capital S will uppercase all the letters in the string h : hashcode A hashcode is like an address. n : newline use %n instead of \n

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String Formatting

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StringBuilder and StringBuffer String objects are immutable Defined equal classes StringBuffer and StringBilder allow changes to lines StringBuffer is synchronized, StringBuilder is not. String s1 = new String("Hello"); String s2 = "And Goodbye"; String str = s1 + s2; str = s1.concat(s2);

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StringBuilder Constructors StringBuilder() StringBuilder(char[] seq) StringBuilder(int capacity) StringBuilder(String str) Methods append(...) adds a string to the end of the buffer. insert(...) adds a string to any location (insert the substring). delete(int begin, int end) deletes a sequence of characters. int capacity() returns the current capacity of the buffer. void ensureCapacity(int i) changes the value of capacity reverse() causes this character sequence to be replaced by the reverse of the sequence

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Regular Expression A regular expression is a kind of pattern that can be applied to text (Strings, in Java) A regular expression either matches the text (or part of the text), or it fails to match If a regular expression matches a part of the text, then you can easily find out which part Beginning with Java 1.4, Java has a regular expression package, java.util.regex The regular expression "[a-z]+" will match a sequence of one or more lowercase letters [a-z] means any character from a through z, inclusive + means “one or more”

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Regular Expression Suppose we apply this pattern to the String "Now is the time" First, you must compile the pattern import java.util.regex.*; Pattern p = Pattern.compile("[a-z]+"); Next, you must create a matcher for a specific piece of text by sending a message to your pattern Matcher m = p.matcher("Now is the time"); Neither Pattern nor Matcher has a public constructor; you create these by using methods in the Pattern class

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Regular Expression Now that we have a matcher m: m.matches() returns true if the pattern matches the entire text string, and false otherwise m.lookingAt() returns true if the pattern matches at the beginning of the text string, and false otherwise m.find() returns true if the pattern matches any part of the text string, and false otherwise If called again, m.find() will start searching from where the last match was found m.find() will return true for as many matches as there are in the string; after that, it will return false When m.find() returns false, matcher m will be reset to the beginning of the text string (and may be used again)

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Regular Expression import java.util.regex.*; public class Appl { public static void main(String[] args) { String pattern = "[a-z]+"; String text = "Now is the time"; Pattern p = Pattern.compile(pattern); Matcher m = p.matcher(text); while (m.find()) { System.out.print(text .substring(m.start(), m.end()) + "*"); } }

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Regular Expression abc exactly this sequence of three letter [abc] any one of the letters a, b, or c [^abc] any character except one of the letters a, b, or c (immediately within an open bracket, ^ mean “not,” but anywhere else it just means the character ^) [a-z] any one character from a through z, inclusive [a-zA-Z0-9] any one letter or digit

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Regular Expression If one pattern is followed by another, the two patterns must match consecutively For example, [A-Za-z]+[0-9] will match one or more letters immediately followed by one digit The vertical bar, |, is used to separate alternatives For example, the pattern abc|xyz will match either abc or xyz X? optional, X occurs once or not at all X* X occurs zero or more times X+ X occurs one or more times X{n} X occurs exactly n times X{n,} X occurs n or more times X{n, m} X occurs at least n but not more than m times

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$Regular Expression . any one character except a line terminator \d a digit: [0-9] \D a non-digit: [^0-9] \s a whitespace character: [ \t\n\x0B\f\r]...$

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Regular Expression . any one character except a line terminator \d a digit: [0-9] \D a non-digit: [^0-9] \s a whitespace character: [ \t\n\x0B\f\r] \S a non-whitespace character: [^\s] \w a word character: [a-zA-Z_0-9] \W a non-word character: [^\w] ^ the beginning of a line $ the end of a line \b a word boundary \B not a word boundary

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Regular Expression In some implementations, a quantifier in regular expressions corresponds to the maximum line length is possible For example, often expect that the expression () will be found in the text tag HTML. However, if the text is more than one HTML-tag, this expression matches the entire string containing a set of tags. Beginning with bold text next, text body,italic text end of text. Solved problem: Take into account characters that are not relevant to the desired pattern (]*> for the above case)

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Regular Expression import java.util.regex.*; public class Appl { public static void main(String[] args) { //String pattern = "[a-z]+"; //String text = "Now is the time"; // //String pattern = ""; //String pattern = "]*>"; //String text = "Beginning with bold text next, text body,italic text end of text."; String pattern = "\\w+(\\.\\w+)*@(\\w+\\.)+\\w+"; String text = "my.mail@ua.ua";

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Regular Expression Pattern p = Pattern.compile(pattern); Matcher m = p.matcher(text); if (m.matches()) { System.out.print("Matches the entire text string"); m.reset(); System.out.println(); } while (m.find()) { System.out.print(text.substring(m.start(),m.end())+ "*"); } } }

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Practical tasks Enter the two variables of type String. Determine whether the first variable substring second. For example, if you typed «IT» and «IT Academy» you must receive true. Enter surname, name and patronymic on the console as a variable of type String. Output on the console: surnames and initials name name, middle name and last name The user name can be 3 to 15 characters of the Latin alphabet, numbers, and underscores. Using regular expressions implement checking the user name for validity. Input five names in the main method . Output a message to the console of the validation of each of the entered names.

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Homework Enter in the console sentence of five words. display the longest word in the sentence determine the number of its letters bring the second word in reverse order Enter a sentence that contains the words between more than one space. Convert all spaces, consecutive, one. For example, if we introduce the sentence "I am learning Java Core», we have to get the "I'm learning Java Core» Implement a pattern for US currency: the first symbol "$", then any number of digits, dot and two digits after the dot. Enter the text from the console that contains several occurrences of US currency. Display all occurrences on the screen.