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Chapter 7 String

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Chapter 7 String …

Chapter 7 String
Taught by Oum Saokosal, Head of Information Technology, National Polytechnic Institute of Cambodia

Published in: Technology, Education

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  • 1. Chapter 7 Strings Oum Saokosal , Head of IT Department National Polytechnic Institute of Cambodia Tel: (855)-12-417214 E-mail: oum_saokosal@yahoo.com
  • 2. Strings p.257
    • Introduction
    • The String class
    • The Character class
    • The StringBuffer class
  • 3. Introduction
    • A string is sequence (series) of characters.
    • A string is NOT an array of characters.
      • E.g. in C/C++: char s[20];
    • In Java, A String is an object.
    • Java has 3 String classes:
      • String
      • StringBuffer
      • StringTokenizer
  • 4. The String class
  • 5. The String class (1)
    • String is in java.lang package.
    • Since java.lang.* is always imported automatically, we don’t need to import the String class.
    • Declaration:
      • String s1;
    • Initialization:
      • s1=“Information Technology”;
    • Or, short-cut:
      • String s1=“Information Technology”;
  • 6. The String class (2)
    • Because String is a class, then s1 is an object.
    • So there should be constructors, methods, or properties.
    • String constructors:
      • String()
      • String(String value)
      • String(char[] value)
      • Ex: String s1 = new String(“IT”);
    • You just say:
      • String s1 = “IT”;
  • 7. The String class (3)
    • Summary of String class
    • Constructors
      • String()
    • Methods
      • charAt()
      • compareTo()
      • concat()
      • endsWidth()
      • equals()
      • getChars()
      • equalsIgnoreCase()
      • getChars()
      • indexOf()
      • lastIndexOf()
      • regionMatches()
      • length()
      • replace()
      • startsWith()
      • subString()
      • toCharArray()
      • toLowerCase()
      • toString()
      • toUpperCase()
      • trim()
      • copyValueOf()
      • valueOf()
  • 8. The String class (4)
    • Q. How do I get those methods to use?
    • A. You just declare a variable as String.
      • String s1=“npic”;
      • Then, you call a method, say length() .
      • System.out.println( s1.length() );
    • Let’s try this out:
      • Public class TestString {
      • public static void main(String[] args){
      • String s1=“npic”;
      • System.out.println(s1.length());
      • }
      • }
  • 9. The String class (5)
    • Note:
    • The String class is immutable (has no setter method).
    • The String class is final so we cannot inherit from it. //Discuss it in chapter 8
    • Lab time:
      • Example 7.1 Checking Palindromes p.266
  • 10. The Character class
  • 11. The Character class
    • To declare a variable as a character, use primitive data type: char .
      • Ex: char ch1 = ‘a’;
    • But Java provides also Character class. It is useful for Data Structure.
      • Ex: Character ch2 = new Character(‘b’);
      • Character ch3 = ‘c’;
    • After define ch2,ch3 as Character, then these can use methods from Character class. Please see methods on page 268.
    • Lab Time:
      • Example 7.2 on page 268
  • 12. The StringBuffer class
  • 13. The StringBuffer class (1)
    • StringBuffer class is more flexible than String class. Why?
    • Because after creating a variable from StringBuffer class, we can use append, delete, insert etc. very easily.
    • Example:
      • StringBuffer sb = new StringBuffer(“NPI”);
      • sb.append(“C”);
  • 14. The StringBuffer class (2)
    • StringBuffer()
    • append():StringBuffer
    • capacity():int
    • charAt():char
    • delete():StringBuffer
    • deleteCharAt():StringBuffer
    • insert():StringBuffer
    • length():int
    • replace():StringBuffer
    • reverse():StringBuffer
    • setCharAt():void
    • setLength():void
    • subString():String
    Homework
  • 15. The StringBuffer class (2)
    • Append
      • StringBuffer st = new StringBuffer("H");
      • st.append('i');
      • st.append(5);
      • st.append(".");
      • st.append("com");
    • //output: Hi5.com
    • Please make some note on the code.
    • StringBuffer provided overloaded methods to append boolean, char, char[], double, float, int, long, String .
  • 16. Lab: Exercise 1
    • Count the number of words in a given String
    • Example:
      • Input: National Polytechnic Institute of Cambodia
      • Output: Word Count: 5 words
  • 17. Lab: Exercise 2
    • On page 285, Section 7.4 The StringBuffer Class
    • 7.11 (Sorting character in a String) Write a method that returns a sorted string using the following header:
    • public static String sort(String s)
    • For example, sort(“bac”) return abc .