new features in jdk8

New Features in JDK 8
Yann.xia

CONTENTS
01
Lambda Expressions
02
Stream API
03
Method Ref
04
Others

Lambda
Expressions
• Lambdas 匿名表达式 (JSR 335)
• Example
(paramters) -> {body}
(x, y) -> x + y

Lambda
Expressions
匿名类 Lambdas
new Thread(new Runnable() {
@Override public void run() {
System.out.print("hi");
}
}).run();
new Thread(() -> System.out.print("hi")).run();

Lambda
Expressions
Multiset<Integer> lengths = HashMultiset.create(
FluentIterable.from(strings)
.filter(new Predicate<String>() {
public boolean apply(String string) {
return
CharMatcher.JAVA_UPPER_CASE.matchesAllOf(string);
}
})
.transform(new Function<String,
Integer>() {
public Integer apply(String string) {
return string.length();
}
}));
匿名类 Lambdas
Multiset<Integer> lengths = HashMultiset.create(
FluentIterable.from(strings)
.filter(string ->
CharMatcher.JAVA_UPPER_CASE.matchesAllOf(string))
.transform(string -> string.length()));

Stream API
Common Stream
List<Transaction> groceryTransactions = new Arraylist<>();
for(Transaction t: transactions){
if(t.getType() == Transaction.GROCERY){
groceryTransactions.add(t);
}
}
Collections.sort(groceryTransactions, new Comparator(){
public int compare(Transaction t1, Transaction t2){
return t2.getValue().compareTo(t1.getValue());
}
});
List<Integer> transactionIds = new ArrayList<>();
for(Transaction t: groceryTransactions){
transactionsIds.add(t.getId());
}
List<Integer> transactionsIds =
transactions.stream()
.filter(t -> t.getType() == Transaction.GROCERY)
.sorted(comparing(Transaction::getValue).reversed())
.map(Transaction::getId)
.collect(toList());

Method References
public static void main(String[] args) {
List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9,
10, 11, 12, 13, 15, 16);
List<Integer> primeNumbers = numbers.stream().filter((x) ->
isPrime(x)).collect(Collectors.toList());
System.out.println("Prime Numbers are " + primeNumbers);
}
public static boolean isPrime(int number) {
/*…*/
}
public static void main(String[] args) {
List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9,
10, 11, 12, 13, 15, 16);
List<Integer> primeNumbers =
numbers.stream().filter(ReferenceToStaticMethodExample::isPr
ime).collect(Collectors.toList());
System.out.println("Prime Numbers are " + primeNumbers);
}

Method References
public static void main(String args[]){
List names = new ArrayList();
names.add("Mahesh");
names.add("Suresh");
names.add("Ramesh");
names.add("Naresh");
names.add("Kalpesh");
names.forEach(System.out::println);
}
public static void main(String args[]){
List names = new ArrayList();
names.add("Mahesh");
names.add("Suresh");
names.add("Ramesh");
names.add("Naresh");
names.add("Kalpesh");
for (Object name : names){
System.out.print(name);
}
}

Others- Date &
Time
//Current Date
LocalDate today = LocalDate.now();
System.out.println("Current Date=" + today);
//Current Time
LocalTime time = LocalTime.now();
System.out.println("Current Time=" + time);
//Current Date
LocalDateTime today = LocalDateTime.now();
System.out.println("Current DateTime=" + today);

Others – default &
static
interface FunctionalDefaultMethods {
void method(); //common
default void defaultMethod() {
System.out.print(this);
//default method
}
static void staticMethod() {
// static method
}
}

Others – Repeatable
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface Filters {
Filter[] value();
}
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Repeatable(Filters.class)
public @interface Filter {
String value();
}
@Filter("filter1")
@Filter("filter2")
public interface Filterable {
}

Others – Param Name
class ParameterNames {
public static void main(String[] args) throws Exception {
Method method =
ParameterNames.class.getMethod("main", String[].class);
for (final Parameter parameter : method.getParameters())
{
System.out.println("Parameter: " +
parameter.getName());
}
}
}
编译时增加 –parameters

new features in jdk8

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