Lecture Notes: Java Strings

Introduction to Java Strings

• Strings: Non-primitive data type, used extensively in Java.
  • Used to define text in programs (e.g., sentences, words, characters).
  • Can store textual data including spaces and special characters.
  • Memory and performance considerations.

Declaration and Definition of Strings

• Declare a string using the String type.

  String name = "Tony";
  String fullName = "Tony Stark";
  String sentence = "My name is Tony Stark.";
  

• Using spaces and special characters in strings.

  String phrase = "Hello, World!";
  

User Input and Scanner Class

• Using Scanner class to get user input.

  Scanner scanner = new Scanner(System.in);
  String userName = scanner.nextLine();
  System.out.println("Your name is " + userName);
  

• Important: Use nextLine() for full sentence input.

  scanner.nextLine() -> for full sentences
  scanner.next() -> for single words
  

String Concatenation

• Concatenating two or more strings using the + operator.

  String firstName = "Tony";
  String lastName = "Stark";
  String fullName = firstName + " " + lastName;
  System.out.println(fullName);
  

String Length

• Calculate the length of a string.

  int length = fullName.length();
  System.out.println("Length: " + length);
  

Access Characters in a String

• Using charAt method to access specific characters in a string.

  for (int i = 0; i < fullName.length(); i++) {
    System.out.print(fullName.charAt(i));
  }
  

Comparing Strings

• Comparing strings with compareTo method.

  int comparison = name1.compareTo(name2);
  

• Returns:
  • Positive: name1 > name2
  • Zero: name1 == name2
  • Negative: name1 < name2
• Example:

  if (comparison == 0) {
    System.out.println("Strings are equal");
  } else {
    System.out.println("Strings are not equal");
  }
  

Using equals for String Comparison

• Difference between compareTo and equals

  if (string1.equals(string2)) {
    System.out.println("Strings are equal");
  }
  

Substrings

• Extracting a substring from a string using the substring method.

  String part = sentence.substring(11, 15); // Extracts "Tony"
  String toEnd = sentence.substring(11); // Extracts "Tony Stark."
  

Immutability of Strings

• Strings are immutable in Java.
  • Once created, their value cannot be changed.
  • Any modifications create a new string.

Summary

• Review of key string functions: declaration, user input, concatenation, length, character access, comparison, and immutability.
• Practice with the provided code snippets.
• StringBuilder introduction in the next class.