Chapter 7 Strings Oum Saokosal , Head of IT Department National Polytechnic Institute of Cambodia Tel: (855)-12-417214 E-mail: oum_saokosal@yahoo.com

Strings p.257 Introduction The String class The Character class The StringBuffer class

Introduction

The String class

The Character class

The StringBuffer class

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

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

The String class

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”;

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”;

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”;

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”;

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()

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()

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()); } }

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());

}

}

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

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

The Character class

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

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

The StringBuffer class

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”);

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”);

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

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

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 .

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 .

Lab: Exercise 1 Count the number of words in a given String Example: Input: National Polytechnic Institute of Cambodia Output: Word Count: 5 words

Count the number of words in a given String

Example:

Input: National Polytechnic Institute of Cambodia

Output: Word Count: 5 words

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 .

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 .