Java 8: Frequently used features
- Interfaces can have static and default methods.
http://www.baeldung.com/java-static-default-methods
Static: Available through interface.
Default: Available through implementing class.
Solution : if any class extending these two interfaces which has same default method, class must ovverride default methods to avoid compile error.
Why default methods? — backward compatibility
https://dzone.com/articles/interface-default-methods-java
2. Method References: Object :: methodName
employees.forEach(System.out::println);3. Functions:
public String add(String string, Function<String, String> fn) {
mreturn fn.apply(string);
}
Function<String, String> fn = parameter -> parameter + " from lambda";
String result = useFoo.add("Message ", fn);
4. What are Lambda expression?
They are anonymous methods used to implement a method defined by a functional interface.
Runnable r= () -> System.out.println("Executing in another thread);
new Thread.start(r);5. Functional Interfaces:
Functional Interface is just like a regular interface, which permits only one abstract method.
Lambda expression is an instance of a functional interface.
Functional interfaces can also have default methods & static methods along with Single abstract method.
6. Streams:
https://medium.com/@sarathmanchu_9050/java8-what-is-streams-355e922be342
books.stream()
.filter(book -> book.year > 2005) // filter out books published in or before 2005
.map(Book::getAuthor) // get the list of authors for the remaining books
.filter(Objects::nonNull) // remove null authors from the list
.map(Author::getName) // get the list of names for the remaining authors
.forEach(System.out::println); // print the value of each remaining element--------------------------------------------------------------------List<Users> userList=users;
int total=userList.stream() //create stream instance from collection
.filter(i->i.status()==married) //intermediate operation
.mapToInt(i->i.age()) //intermediate operation
.sum() //Terminal operation kicks off all operations
- Sum of array:
int sum = Arrays.stream(myIntArray)
.sum();2. Count empty String in Java 8
long count = list.stream().filter(String::isEmpty).count();
3. Optional to return list or null
List<String> listOpt = getList().orElseGet(ArrayList::new);
Advantages of Java 8 Optional:
Null checks are not required.
No more NullPointerException at run-time.
We can develop clean and neat APIs.
No more Boiler plate code
Optional<String> opt = Optional.of("baeldung");
opt.ifPresent(name -> System.out.println(name.length()));
Optional<String> optional = Optional.ofNullable(getString());
Optional<String> opt = Optional.of("baeldung");
opt.ifPresent(name -> System.out.println(name.length()));
orElse : provides value in case of null.
orElseGet: provides functional interfaces
String name = Optional.ofNullable(nullName).orElse("john");
String name = Optional.ofNullable(nullName).orElseGet(() -> "john");
5. forEach in Iterable Interface
l.forEach((a)->System.out.println(a));
---------------------------------------------myList.forEach(new Consumer<Integer>() {
public void accept(Integer t) {
System.out.println("forEach anonymous class Value::"+t);
}
});
6. Map lets you convert one object type to another object type.
List<String> collect = alpha.stream().map(String::toUpperCase).collect(Collectors.toList());7. Filter a null value from the List
List<String> result = language.filter(x -> x!=null).collect(Collectors.toList());List<String> result = language.filter(Objects::nonNull).collect(Collectors.toList());
8. Date / Time API : Inspired with Joda time library
http://www.baeldung.com/java-8-date-time-intro
LocalDate tomorrow = LocalDate.now().plusDays(1);When to use parallelStream()?
Internally uses fork-join pool.
myList.parallelStream().sum()
