part1

Main changes from java-8 to java-17

New var keyword

• A new var keyword was added that allows local variables to be declared in a more concise manner,
• Ex:

  var name = new String("hello");
  System.out.println(name); // hello
  
  var student = new Student(121,"Doniel",5.9);
  System.out.println(student.getName()); // Doniel
  System.out.println(student.getHeight()); // 5.9

Extended switch expressions

• Cleaner and less error-prone syntax,
• case label followed by -> followed by one of the following:
  • An expression, including but not limited to a constant value,
  • A throw statement,
  • A code block using opening and closing curly brackets
• Ex:

  int i = 20;
  switch (i){
      case 10 -> {
          System.out.println(10);
          System.out.println("10");
      }
      case 20-> System.out.println(20); // executed
      default-> System.out.println("Other");
  }
  
  i = 40;
  String message = switch (i){
      case 10 -> "10";
      case 20 -> "20";
      case 30 -> throw new RuntimeException("idk");
      case 40 ->{
          System.out.println("40"); // executed
          yield "like return";
      }
      default -> "none";
  };
  
  System.out.println(message); // like return

instanceof pattern matching

• Till now, we do like this

  Student student = new PartTimeStudent(12,"Imran",5.5,12);
  PartTimeStudent partTimeStudent;
  if(student instanceof PartTimeStudent){
    partTimeStudent = (PartTimeStudent)student; 
  }

• Above can be simplified like this:

  Student student = new PartTimeStudent(12,"Imran",5.5,12);
          
  if(student instanceof PartTimeStudent partTimeStudent){
    // partTimeStudent
  }

Sealed Classes

• Another way to disable inheritance introduced in Java 17,
• Allows you to define a class and exactly what classes can subclass it,
• Subclass of Sealed class must define their status: final, sealed, or non-sealed,
• Ex(Sealed class):

  public abstract sealed class Security permits Lock, Pin, Password { }

  Inheriting sealed-class:

  final class Lock extends Security{ } // no class can inherit it
  
  non-sealed class Pin extends Security{ } // any class can inherit it
  
  sealed class Password extends Security permits MyPassword{ } // same as sealed

  Inhering subclass of sealed-class,

  final class MyPassword extends Password{} // inherited above sealed class
  
  class MyPin extends Pin{} // Since Pin class can be inherited by any class

Multiline Strings

• Is done via TextBlocks,
• A text block must start
  • with three quotation marks, then
  • a new line, then
  • your text as you write normally,
• Ex(Earlier way):

  String formattedTextEarlier = "This is first line.\n"+
          "THis is second line.\n"+
          "Continue like that";
  System.out.println(formattedTextEarlier);

  New way:

  String formattedText = """
          This is first line.
          THis is second line.
          Continue like that""";
  System.out.println(formattedText);

  Output:

  This is first line.
  THis is second line.
  Continue like that
  

  Below one is invalid since uou can't write just after first """,

  String formattedText2 = """This is first line.
          THis is second line.
          Continue like that""";

Record

• Previous way:

  public class Person {
      final String name;
      final int age;
  
      public Person(String name, int age) {
          this.name = name;
          this.age = age;
      }
  
      public String getName() {
          return name;
      }
  
      public int getAge() {
          return age;
      }
  }

  New way:

  public record PersonRecord(String name, int age) { }

  Using like this:

  Person student = new Person("Saeed",2345);
  
  PersonRecord record = new PersonRecord("Saeed",2345);
  
  System.out.println(student.getName() + " - " + record.name()); // Saeed - Saeed
  System.out.println(student.getAge() + " - " + record.age()); // 2345 - 2345