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String Regular Expression. Java Core

1: String Regular Expression Java Core

2: Agenda Java String methods String StringBuffer StringBuilder Regular Expression Practical tasks

3: 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 doesnt has a primitive type!!!

4: 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.

5: 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

6: 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();

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

8: 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)

9: Basic methods Working with case of symbols String toLowerCase() String toUpperCase() Trim strings String str "tTabulated Stringt"; String tStr str. trim(); Replace symbols String str "abracadabra"; String rStr str. replace(a, o); boolean isEmpty()

10: 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());

11: String Constant Pool

12: 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

13: 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);

14: 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

15: String Formatting

16: 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);

17: 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

18: 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

19: 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

20: 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)

21: 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()) "");

22: Regular Expression abcexactly this sequence of three letter abcany one of the letters a, b, or c abcany 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-zany one character from a through z, inclusive a-zA-Z0-9any one letter or digit

23: Regular Expression If one pattern is followed by another, the two patterns must match consecutively For example, A-Za-z0-9 will match one or more letters immediately followed by one digit The vertical bar, , is used to separate alternatives For example, the pattern abcxyz will match either abc or xyz X?optional, X occurs once or not at all XX occurs zero or more times XX occurs one or more times XnX occurs exactly n times Xn,X occurs n or more times Xn, mX occurs at least n but not more than m times

24: Regular Expression . any one character except a line terminator da digit: 0-9 Da non-digit: 0-9 sa whitespace character: tnx0Bfr Sa non-whitespace character: s wa word character: a-zA-Z0-9 Wa non-word character: w the beginning of a line $the end of a line ba word boundary Bnot a word boundary

25: 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)

26: 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. mailua. ua";

27: 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()) "");

28: 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.

29: 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 "Im 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.

30: The end

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