Java 17

Feature Name Description
New Licence Java 17 is issued under the new NFTC (Oracle No-Fee Terms and Conditions) license. It is therefore again allowed to use the Oracle JDK version for free for production and commercial use.
Text Blocks
Preview in Java 13		 Triple quotes """ text blocks allowed
private static void jsonBlock() {
    String text = """
            {
              "name": "John Doe",
              "age": 45,
              "address": "Doe Street, 23, Java Town"
            }
            """; // the indent of ending could determine the preceding spaces for block
    System.out.println(text);
}
Switch Expressions
Simplier format, more compact no break; needed		 
private static void withSwitchExpression(Fruit fruit) {
    switch (fruit) {		// could be assigned to var like String res = switch ...
        case APPLE, PEAR -> System.out.println("Common fruit");
        case ORANGE, AVOCADO -> System.out.println("Exotic fruit");
        default -> System.out.println("Undefined fruit");
    }
}
Records
Records will allow you to create simple immutable data classes.
Preview in Java 14 
public record GrapeRecord(Color color, int nbrOfPits) {
// no need to define getters etc. Can override constructor.
}
// Also possible to define anywhere in the code
    record GrapeRecord(Color color, int nbrOfPits) {}
    GrapeRecord grape1 = new GrapeRecord(Color.BLUE, 1);
Sealed Classes
more a feature useful for library owners. Let you allow who can extend abstract class and who cannot
Preview in Java 15 
public abstract sealed class FruitSealed permits AppleSealed, PearSealed {
}
public non-sealed class AppleSealed extends FruitSealed {
}
public final class PearSealed extends FruitSealed {
}
Pattern matching for instanceof Preview in Java 14 
     if (o instanceof GrapeClass grape) { // now can auto assign grape to o with casting to class
         System.out.println("This grape has " + grape.getNbrOfPits() + " pits.");
     }
Helpful NullPointerExceptions
In Java 14		 With Java 17, the same code results in the following output which shows exactly where the NullPointerException occured at which class/instance.
Compact Number Formatting Support
A factory method is added to NumberFormat in order to format numbers in compact, human-readable form 		NumberFormat fmt = NumberFormat.getCompactNumberInstance(Locale.ENGLISH, NumberFormat.Style.SHORT);
Outputs like:
1K, 100K, 1M
or 1 thousand, 100 thousand, 1 million
Day Period Support Added
A new pattern B is added for formatting a DateTime which indicates a day period according to the Unicode standard. 
DateTimeFormatter dtf = DateTimeFormatter.ofPattern("B");
System.out.println(dtf.format(LocalTime.of(8, 0)));
Outputs like:
in the morning, in the afternoon, in the evening, at night, midnight
Stream.toList()
In order to convert a Stream to a List, you need to call the collect method with Collectors.toList(). In Java 17, a toList method is added which replaces the old behaviour. 
    Stream stringStream = Stream.of("a", "b", "c");
    List stringList =  stringStream.toList();
    for(String s : stringList) {
        System.out.println(s);
    }