New Things in Java8

New Things in Java8

1. Functional Interface

 

2. Lambda

public int sum(int x, int y){

     return x + y;

}

 

(int x, int y) -> { return x + y; }

java8 can guess and decide the type

(x, y) -> { return x + y;}

 

The magic part is the comparator class

Comparator comparator = (str1,str2) -> {return s1.compareToIgnoreCase(s2);}

 

3. Function as first-class object

Function<String, String> upperfier = String::toUpperCase;

System.out.println(upperfier.apply(“Hello"));

 

Predicate

Set<String> knowNames = new HashSet<>();

knowNames.add(“sillycat");

knowNames.contains(“sillycat");

 

Predicate<String> isKnowName = knowNames::contains;

isKnowName.test(“sillycat");

 

4. More Static Methods

Public static <T, U extends Comparable<? super U>> Comparator<T> comparing(Function<? super T, ? extends U> keyExtractor){}

 

Compare Name

Comparator nameComparator = Comparator.comparing(Emloyee::getName);

Compare Salary

Comparator salaryComparator = Comparator.comparing(Employee::getSalary);

 

5. Stream

map, filter, reduce

//list sum

int result = list.stream().reduce(0, (x,y) -> x+y);

 

//list filter

int result = list.stream().filter(x -> x > 5).reduce(0, (x,y) -> x+y);

 

//list map

int result = list.stream().filter(x->x>5).map(x->x*x).mapToInt(x->x).sum();

 

Really Nice

//salary sum

int totalSalary = employees.stream().map(e->e.getSalary()).reduce(0,(x,y)->x+y);

 

double averageSalary = employees.stream().mapToInt(e->e.getSalary()).average().getAsDouble();

 

Just read these 2 blogs, java8 really contains a lot of nice things. Need to read the book when I begin to use a lot of that.

 

References:

http://junlintianxia.iteye.com/blog/2003087

https://chou.it/2014/03/java-8-new-features/