The slides presented in Android Taipei event on Feb 25, 2016

1. Gance
淺談CLOSURE

3. Many of modern programming
languages supports Closure.

4. Is Java going to support Closure?

6. A closure (閉包) is a function
that has an environment of its
own

7. Closures are a technique for
implementing lexically scoped
name binding in languages with
first-class functions.

8. Closure Example 1
js> function doSome() {
> var x = 10;
> function f(y) {
> return x + y;
> }
> return f;
> }
js> var foo = doSome();
js> foo(20);
30
js> foo(30);
40

9. Closure Example 2
js> function doOther() {
> var x = 10;
> function f(y) {
> return x + y;
> }
> x = 100;
> return f;
> }
js> var foo = doOther();
js> foo(20);
120
js> foo(30);
130

10. Closure Example 3
js> function doOther() {
> var x = 10;
> function f() {
> x--;
> return x;
> }
> return f;
> }
js> var f1 = doOther();
js> var f2 = doOther();
js> f1();
9
js> f2();
9

11. More About Closure
 Closure是擁有閒置變數（Free variable）的運
算式。
 如果函式的閒置變數與當時語彙環境（Lexical
environment）綁定，該函式才稱為Closure。
 Closure關閉的是變數的reference，而不是變數
的value

12. Java 8 introduces the support
for Lambda. Is it Closure?

13. Lambda Expression
 A lambda expression is an “anonymous
function”
 a method without a declaration (access
modifier, return value declaration, and name)
 Syntax: (argument) -> (body)
(int a, int b) -> { return a + b; }
() -> System.out.println("Hello World");
(String s) -> { System.out.println(s); }
() -> 42
() -> { return 3.1415 };

14. Lambda Example 1
//Old way:
new Thread(new Runnable() {
@Override
public void run() {
System.out.println("Hello from thread");
}
}).start();
//New way:
new Thread(
() -> System.out.println("Hello from thread")
).start();

15. Lambda Example 2
//Old way:
button.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
System.out.println("The button was clicked using old fashion code!");
}
});
//New way:
button.addActionListener( (e) -> {
System.out.println("The button was clicked. From lambda expressions !");
});

16. Lambda Example 3
public static void main(String[] args) {
int number = 5;
ObjectCallback callback = () -> {
return (number = number + 1);
};
Object result = callback.Callback();
System.out.println(result);
}
number should be effectively final

17. Conclusion
 A closure is any function which closes over
the environment in which it was defined.
 A lambda is just an "anonymous function" - a
function defined with no name.
 Lambda in Java 8 is NOT closure!

18. 歐美防毒/安全軟體的領導品牌Avast Software台北辦公
室，徵一名資深Android RD (Android Tech-Lead
Developer)
• 與頂尖的Android RD、architect一同開發給全世界數千萬使用
者使用的app
• Onboard後立即到美麗的捷克布拉格training三週以上
• 每年公司全額補助一次參加類似Google I/O的大型conference
• 15天年假 ＋彈性工時 ＋(partial) remote working
• 詳見
http://www.104.com.tw/job/?jobno=4hqzm&jobsource=checkc
歡迎熱愛app、熟悉OO的Android高手加入我們！