The document discusses the String class in Java and string processing. It covers that strings are immutable sequences of characters, how they are created and stored, and the differences between using the String, StringBuffer, and StringBuilder classes. It also summarizes common string methods and how to compare strings using the == operator, equals() method, and compareTo() method.

1. Text Processing

2. String class
 Represents character strings.
 String is a sequence of Characters.
 Strings are Immutable.

3. Creation of Strings
String word1 = “Java”;
String word2 = “Java”;
String word1 = new String(“Java”);
String word2 = new String(“Java”);
word1
String Constant Pool Heap Memory
“Java”
“Java”
“Java”
word2
word1
word2
Using String Literal Using new keyword

4. Immutability
 Once created, a string cannot be changed.
Example:
String hostName = ''localhost'';
hostName.concat(''host'');
System.out.println(hostName); // localhost (immutable)

5. Disadvantage Of Immutability
• Need to create new String even for small change.
Example:
String school = ''hogwarts'';
char ch = Character.toUpperCase(school.charAt (0));
school = ch + school.substring(1); // Hogwarts
school
“Hogwarts”
“hogwarts”

6. StringBuffer Class
 Mutable, Synchronized
 toString() method is used to convert StringBuffer
to String
Example:
StringBuffer name = new StringBuffer("Hello");
name.append(" World");
System.out.println(name); // Hello World

7. StringBuilder Class
• StringBuilder is the same as the StringBuffer
class.
• Not synchronized.
• High Performance.

8. String Class Methods

int length()

char chatAt(int index)

String concat(String str)

String substring(int beginIndex, int endIndex)

int indexOf(char) / int indexOf(char, int)

String trim()

String replace(char oldChar, char newChar)

String toUpperCase()

String toLowerCase()

9. StringBuffer Methods
• int capacity()
• StringBuffer append()
• void setCharAt(int index, char ch)
• StringBuffer delete(int start, int end)
• StringBuffer reverse()

10. Comparison of Strings
 == operator
 boolean equals(Object obj)
 int compareTo(String str)

11. == operator
 == operator compares references not values.
Example:
class Test {
public static void main(String args[]) {
String s1 = "Wizard";
String s2 = "Wizard";
String s3 = new String("Wizard");
System.out.println(s1 == s2);// true
System.out.println(s1 == s3);// false
}
}

12. equals()
Example:
String s1 = "java";
String s2 = "java";
String s3 = new String("java");
String s4 = new String("java");
System.out.println(s1.equals(s2)); // true
System.out.println(s1.equals(s3)); // true
System.out.println(s3.equals(s4)); // true
StringBuffer sb1 = new StringBuffer("string");
StringBuffer sb2 = new StringBuffer("string");
System.out.println(sb1.equals(sb2)); // false
equals() method compares the content of the string.

13. CompareTo()
compareTo() method compares values lexicographically and
returns an integer value.
Example:
class CompareTo {
public static void main(String args[]) {
String s1 = "Jack";
String s2 = "Rose";
String s3 = "Jordan";
String s4 = new String("Rose");
System.out.println(s1.compareTo(s2));// -8 (J=74 R=82)
System.out.println(s3.compareTo(s1));// 14 (A=65 O=79)
System.out.println(s1.compareTo(s4));// 0
}
}