Groovy

Difference with Java

1.Groovy默认已经import了部分的包和类

2.multi-methods | runtime dispatch

groovy:method chosen at runtime base on types of arguments
java: method chosen at compile time base on declared types

3.数组初始化

大括号已经保留给闭包使用。数组的初始化使用中括号

int[] array = [1,2,3]

4.类的可见域

java: 默认是 'package private'，只有在同一个包里面才能访问到
groovy: 默认是public

5.semicolon is optional

6.parentheses is optional

普通调用，括号可要可不要
对于closure来说，不写括号是对closure的引用。带括号是对closure的调用
当函数调用嵌套是，需要括号

7.return keyword is optional

最后的值会被返回

No matter what type of object we try to return, the return type defined in the method will determine the type that is actually returned
However, if the method uses the def keyword as its return type, then the return type is considered to be dynamic
No matter what value is contained in the last statement in a method, if the return type is void, the value returned will always be null

8.dynamic type

explicit type
use def keyword, decide at runtime later

9.ARM blocks

ARM (Automatic Resource Management) block

10.source file contain both class definitions and inline scripting.

when compile, generate a class object for each Groovy class
generate a class for scripting elements
Groovy scripts have a special binding for variable references

11.GroovyBeans || POGO (Plain Old Groovy Object)

Groovy automatically generates getters and setters for instance fields in a class that have the default visibility of public.
It also generates a default constructor.
field dereference operator @. directly access the field without going through a getter or setter

12.GroovyBeans && map

every groovybean has default built-in Map constructor
map中如果包含有不相关的属性，会直接抛异常

13.Autoboxing

as if primitives don't exist
treat any numeric value as if both an object-base numeric and a primitive

14.Strings

Normal strings in Groovy are instances of the java.lang.String class
Strings that contain the ${...} syntax are instantiated as Groovy GString objects

15.Closures, on the other hand, can reference variables from outside their own scope

given: "a variable in scope"
       def greeting = "Hello"
   and: "a closure that can access the variable"
       def greet = { println "$greeting, World!"}
   when: "we invoke the closure with variable different"
       greet()
       greeting = "Goodbye"
       greet()
   then: "the output is as expected"
       """Hello, World!
   Goodbye, World!""" == output()

16.Groovy Truth （true/false）

非0都是true
null 空值，空串，空的集合都是false，否则都是true

17.<=> , Spaceship operator

Spaceship is a shorthand operator that works the same as Java's compareTo method.

Groovy，一句话