Java的闭包 详解Java的闭包

public void anonymousExample() {
  String nonFinalVariable = "Non Final Example";
  String variable = "Outer Method Variable";
  new Thread(new Runnable() {
    String variable = "Runnable Class Member";
    public void run() {
      String variable = "Run Method Variable";
      //Below line gives compilation error.
      //System.out.println("->" + nonFinalVariable);
      System.out.println("->" + variable);
      System.out.println("->" + this.variable);
    }
  }).start();
}

->Run Method Variable
->Runnable Class Member

interface Runnable { void run(); }
// Functional
interface Foo { boolean equals(Object obj); }
// Not functional; equals is already an implicit member
interface Bar extends Foo {int compare(String o1, String o2); }
// Functional; Bar has one abstract non-Object method
interface Comparator {
 boolean equals(Object obj);
 int compare(T o1, T o2);
}
// Functional; Comparator has one abstract non-Object method
interface Foo {int m();  Object clone(); }
// Not functional; method Object.clone is not public
interface X { int m(Iterable arg); }
interface Y { int m(Iterable arg); }
interface Z extends X, Y {}
// Functional: two methods, but they have the same signature

(String s)-> s.lengh;
() -> 43;
(int x, int y) -> x + y;

public class FirstLambdaExpression {
  public String variable = "Class Level Variable";
  public static void main(String[] arg) {
    new FirstLambdaExpression().lambdaExpression();
  }
  public void lambdaExpression(){
    String variable = "Method Local Variable";
    String nonFinalVariable = "This is non final variable";
    new Thread (() -> {
      //Below line gives compilation error
      //String variable = "Run Method Variable"
      System.out.println("->" + variable);
      System.out.println("->" + this.variable);
    }).start();
  }
}

->Method Local Variable
->Class Level Variable

//Lambda expression is enclosed within methods parameter block.
//Target interface type is the methods parameter type.
String user = doSomething(() -> list.getProperty(“propName”);
//Lambda expression is enclosed within a thread constructor
//target interface type is contructors paramter i.e. Runnable
new Thread (() -> {
  System.out.println("Running in different thread");
}).start();

Comparator c = (s1, s2) -> s1.compareToIgnoreCase(s2);

ActionListenr listenr = event -> event.getWhen();

void invoke(Runnable r) {r.run()}
void Future invoke(Callable r) {return c.compute()}
//above are two methods, both takes parameter of type functional interface
Future s = invoke(() ->"Done"); //Which invoke will be called?

public class FirstSightWithLambdaExpressions {
  public static void main(String[] args) {
    List list = Arrays.asList(
      (Callable)()->"callable 1",
      (Callable) ()->"callable 2",
      (Callable) ()->"callable 3");
    ExecutorService e = Executors.newFixedThreadPool(2);
    List futures = null;
    try {
      futures = e.invokeAll(list);
      new FirstSightWithLambdaExpressions().dumpList(futures);
    } catch (InterruptedException | ExecutionException e1) {
      e1.printStackTrace();
    }
    e.shutdown();
  }
  public void dumpList(List list) throws InterruptedException,
       ExecutionException {
    for (Future future : list) {
      System.out.println(future.get());
    }
  }
}

System::getProperty
"abc"::length
String::length
super::toString
ArrayList::new

import java.util.Arrays;
import java.util.List;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;
public class MethodReference {
  public static void main (String[] ar){
    Employee[] employees = {new Employee("Nick"), new Employee("Robin"), new      Employee("Josh"), new Employee("Andy"), new Employee("Mark")};
    System.out.println("Before Sort:");
    dumpEmployee(employees);
    Arrays.sort(employees, Employee::myCompare);
    System.out.println("After Sort:");
    dumpEmployee(employees);
  }
  public static void dumpEmployee(Employee[] employees){
    for(Employee emp : Arrays.asList(employees)){
      System.out.print(emp.name+", ");
    }
    System.out.println();
  }
}
class Employee {
  String name;
  Employee(String name) {
   this.name = name;
  }
  public static int myCompare(Employee emp1, Employee emp2) {
    return emp1.name.compareTo(emp2.name);
  }
}

Before Sort: Nick, Robin, Josh, Andy, Mark, 
After Sort: Andy, Josh, Mark, Nick, Robin,

public static int myCompare(Employee emp1, Employee emp2) {
 return emp1.name.compareTo(emp2.name);
}
//Another method with the same name as of the above.
public static int myCompare(Integer int1, Integer int2) {
 return int1.compareTo(int2);
}

Employee[] employees = {new Employee("Nick"), new Employee("Robin"),
     new Employee("Josh"), new Employee("Andy"), new Employee("Mark")};
Integer[] ints = {1 , 4, 8, 2, 3, 8, 6};

Arrays.sort(employees, Employee::myCompare);
Arrays.sort(ints, Employee::myCompare);

Arrays.sort(ints, Integer::compareTo);

public class ConstructorReference {
  public static void main(String[] ar){
    MyInterface in = MyClass::new;
    System.out.println("->"+in.getMeMyObject());
  }
}
interface MyInterface{
  MyClass getMeMyObject();
}
class MyClass{
  MyClass(){}
}

->com.MyClass@34e5307e

public class ConstructorReference {
  public static void main(String[] ar){
    EmlpoyeeProvider provider = Employee::new;
    Employee emp = provider.getMeEmployee("John", 30);
    System.out.println("->Employee Name: "+emp.name);
    System.out.println("->Employee Age: "+emp.age);
  }
}
interface EmlpoyeeProvider{
  Employee getMeEmployee(String s, Integer i);
}
class Employee{
  String name;
  Integer age;
  Employee (String name, Integer age){
    this.name = name;
    this.age = age;
  }
}

->Employee Name: John
->Employee Age: 30

public class DefaultMethods {
 public static void main(String[] ar){
 NormalInterface instance = new NormalInterfaceImpl();
 instance.myNormalMethod();
 instance.myDefaultMethod();
 }
}
interface NormalInterface{
 void myNormalMethod();
 void myDefaultMethod () default{
 System.out.println("-> myDefaultMethod");
 }
}
class NormalInterfaceImpl implements NormalInterface{
 @Override
 public void myNormalMethod() {
 System.out.println("-> myNormalMethod");
 }
}

-> myDefaultMethod

interface ParentInterface{
 void initiallyNormal();
 void initiallyDefault () default{
 System.out.println("-> myDefaultMethod");
 }
}
interface ChildInterface extends ParentInterface{
 void initiallyNormal() default{
 System.out.println("now default - > initiallyNormal");
 }
 void initiallyDefault (); //Now a normal method
}

public class DefaultMethods {
 public static void main(String[] ar){
 Interfaxe impl = new NormalInterfaceImpl();
 impl.defaultMethod();
 }
}
class ParentClass{
 public void defaultMethod() {
 System.out.println("->ParentClass");
 }
}
interface Interfaxe{
 public void defaultMethod() default{
 System.out.println("->Interfaxe");
 }
}
class NormalInterfaceImpl extends ParentClass implements Interfaxe{}

->ParentClass

public class DefaultMethods {
 public static void main(String[] ar){
 FirstInterface impl = new NormalInterfaceImpl();
 impl.defaultMethod();
 }
}
interface FirstInterface{
 public void defaultMethod() default{
 System.out.println("->FirstInterface");
 }
}
interface SecondInterface{
 public void defaultMethod() default{
 System.out.println("->SecondInterface");
 }
}
class NormalInterfaceImpl implements FirstInterface, SecondInterface{
 public void defaultMethod(){
 SecondInterface.super.defaultMethod();
 }
}

->SecondInterface