Strings In OOP(Object oriented programming)

Strings In OOP(Object oriented programming)

• 1.
  Packages
• 2.
  Creating package • includea package command as the first statement in a Java source file. – the classes declared within that file will belong to the specified package. • The package statement defines a name space in which classes are stored. – the class names are put into the default package, which has no name. package pkg; package pkg1[.pkg2[.pkg3]]; e.g., package java.awt.image;
• 3.
  Access Protection
• 4.
  Strings
• 5.
  Strings • Strings arefundamental part of all computing languages. • At the basic level, they are just a data structure that can hold a series of characters • However, strings are not implemented as a character array in Java as in other languages.
• 6.
  Strings in Java •Strings are implemented as two classes in Java • java.lang.String provides an unchangeable String object • java.lang.StringBuffer provides a String object that can be amended
• 7.
  Basic String Methods •length() returns the length of the string • toLowerCase() converts the string to lower case • toUpperCase() converts the string to upper case • replace(char, char) replaces occurrences of one character with another character
• 8.
  Basic Strings continued •Basic strings are not meant to change frequently so there are no add or append methods • However the concat(String) method does allow two strings to be concatenated together
• 9.
  Basic Strings continued •Substrings of a String object can also be accessed • A portion of String object can be copied to a character array using the getChars() method • The substring() method can return substring beginning at a specified offset
• 10.
  Searching a string •Methods for searching strings – indexOf(x) searches for the first occurrence of x – indexOf(x, y) searches for the first occurrence of x after the offset of y – lastIndexOf(x) searches backwards for the first occurrence of x – lastIndexOf(x, y) searches backwards for the first occurrence of x after the offset of y
• 11.
  Example of stringsearch • indexOf(x) and indexOf(x, y) can find all occurrences of a character(s) in a string public void paint(Graphics g) { String str = new String("Wish You Were Here"); int count = 0; int fromIndex = 0; while(fromIndex != -1) { fromIndex = str.indexOf("er", fromIndex); if (fromIndex != -1) { count++; fromIndex++; } } g.drawString(String.valueOf(count), 10, 10); }
• 13.
  Parsing Strings • Stringscan be parsed with the StringTokenizer class • The default delimiters (space, tab, newline and carriage return) can be used for parsing sentences • By specifying different delimiters, a wide variety of strings may be parsed
• 14.
  Parsing Strings continued •Different default constructors are provided – Tokenize the string based on the default delimiters – Tokenize the string based on a specified set of delimiters – Tokenize the string based on a specified set of delimiters with a boolean flag to specify whether the delimiters should also be returned as tokens
• 15.
  StringBuffer class • TheStringBuffer class is provided for strings that need may need to be changed • The StringBuffer class contains methods for both inserting and appending text • An object created as a StringBuffer can easily be converted to an object of the String class if needed
• 16.
  More on StringBufferClass • Conversion may be needed because many Java library methods expect a string • The toString() method is used for converting a StringBuffer object to a String object • Example of converting a StringBuffer to a String: public void paint(Graphics g) { StringBuffer buf = new StringBuffer("Hello, World"); g.drawString(buf.toString(), 10, 10); }
• 17.
  More on StringBufferClass • StringBuffer objects are mutable and capacity & length affect performance • If the StringBuffer object needs to be expanded during an append or insert, a new array is created and the old data copied to it • Use capacity() and ensureCapacity(int) methods to minimize expansions
• 18.
  Length v. Capacity •The length() method returns the length of the string in the StringBuffer • The capacity() method returns the total “space” in a StringBuffer • The ensureCapacity(int) method insures the StringBuffer has at least the specified amount of capacity remaining
• 19.
  Length v. Capacitycon’t • Examples of length() and capacity() methods StringBuffer buf = new StringBuffer(25);// creates StringBuffer with length 25 buf.append("13 Characters"); // appends 13 characters int len = buf.length(); // length() returns 13 int cap = buf.capacity(); // capacity returns 25
• 20.
  Bibliography • http://www.eimc.brad.ac.uk/java/tutorial/Pro ject/4/string.htm • http://www.scism.sbu.ac.uk/jfl/Appa/appa5.h tml •http://docs.rinet.ru:8080/WebJPP/contents.ht m • http://www.javaworld.com/javaworld/jw-10- 2002/jw-1004-java101guide.html