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
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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
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However, if the method uses the def keyword as its return type, then the return type is considered to be dynamic
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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.