Chapter 7 Strings

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Chapter 7 Strings

• Oum Saokosal, Head of IT Department
• National Polytechnic Institute of Cambodia
• Tel [phone]
• E-mail oum_saokosal_at_yahoo.com

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Strings p.257

• Introduction
• The String class
• The Character class
• The StringBuffer class

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Introduction

• A string is sequence (series) of characters.
• A string is NOT an array of characters.
• E.g. in C/C char s20
• In Java, A String is an object.
• Java has 3 String classes
• String
• StringBuffer
• StringTokenizer

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The String class
5
The String class (1)

• String is in java.lang package.
• Since java.lang. is always imported
  automatically, we dont need to import the String
  class.
• Declaration
• String s1
• Initialization
• s1Information Technology
• Or, short-cut
• String s1Information Technology

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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

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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()

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The String class (4)

• Q. How do I get those methods to use?
• A. You just declare a variable as String.
• String s1npic
• Then, you call a method, say length().
• System.out.println(s1.length())
• Lets try this out
• Public class TestString
• public static void main(String args)
• String s1npic
• System.out.println(s1.length())

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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

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The Character class
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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

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The StringBuffer class
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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)

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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
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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.

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Lab Exercise 1

• Count the number of words in a given String
• Example
• Input National Polytechnic Institute of
  Cambodia
• Output Word Count 5 words

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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.