groovy-语句
2013-10-02 01:22 Rollen Holt 阅读(6819) 评论(0) 编辑 收藏 举报groovy语句类似于java语句,但是在groovy中的分号”;”是可选的。比如:
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def x = [ 1 , 2 , 3 ] |
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println x |
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def y = 5 ; def x = y + 7 |
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println x |
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assert x == 12 |
而且对于一些方法参数等复杂的事情,我们可以横跨多行:
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def x = [ 1 , 2 , 3 , |
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4 , 5 , 6 ] |
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println ( |
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x |
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) |
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if (x != null && |
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x. size () > 5 ) { |
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println ( "Works!" ) |
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} |
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else { |
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assert false: "should never happen ${x}" |
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} |
groovy支持一行给多个变量赋值:
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def (a, b) = [ 1 , 2 ] |
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assert a == 1 |
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assert b == 2 |
这就使得我们的方法可以返回多个值了,比如返回经纬度的方法:
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def geocode(String location) { |
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// implementation returns [48.824068, 2.531733] for Paris, France |
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[ 48.824068 , 2.531733 ] |
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} |
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def (_lat, _long) = geocode( "Paris, France" ) |
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assert _lat == 48.824068 |
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assert _long == 2.531733 |
当然我们也可以定义方法的参数类型:
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def ( int i, String s) = [ 1 , 'Groovy' ] |
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assert i == 1 |
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assert s == 'Groovy' |
对于事先已经定义好的变量,我们在赋值的时候不需要def关键字:
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def firstname, lastname |
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(firstname, lastname) = "Guillaume Laforge" . tokenize () |
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assert firstname == "Guillaume" |
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assert lastname == "Laforge" |
当然,在赋值的时候可能会出现两侧的数量不一致的情况,比如当左侧数量多于右侧的时候,左侧多出来的为null:
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def elements = [ 1 , 2 ] |
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def (a, b, c) = elements |
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assert a == 1 |
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assert b == 2 |
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assert c == null |
但是当右侧的多于左侧的时候,多出来的不赋值。
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def elements = [ 1 , 2 , 3 , 4 ] |
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def (a, b, c) = elements |
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assert a == 1 |
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assert b == 2 |
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assert c == 3 |
根据groovy的语法,我们可以在一行中swap两个变量:
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// given those two variables |
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def a = 1 , b = 2 |
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// swap variables with a list |
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(a, b) = [b, a] |
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assert a == 2 |
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assert b == 1 |
注释:
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print "hello" // This is a silly print statement |
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/* This is a long comment |
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about our favorite println */ |
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println "hello" |
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// This doesn't work: |
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# Bad comment |
我们可以发现#其实并不是注释字符。
方法调用
groovy中的方法调用类似于java,比如:
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class Foo { |
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def calculatePrice() { |
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1.23 |
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} |
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static void main(args) { |
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def foo = new Foo() |
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def p = foo.calculatePrice() |
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assert p > 0 |
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println "Found price: " + p |
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} |
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} |
可选的括号
在groovy中,Groovy中的方法调用可以省略括号,如果有至少一个参数,并且不存在任何含糊。比如:
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println "Hello world" |
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System.out. println "Nice cheese Gromit!" |
在命名参数的时候,也是可以省略的:
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compare fund: "SuperInvestment" , withBench: "NIKEI" |
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monster.move from: [ 3 , 4 ], to: [ 4 , 5 ] |
命名参数传递
当调用一个方法时,你可以通过在命名参数。参数名称和值之间由一个冒号,比如:
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def bean = new Expando(name: "James" , location: "London" , id: 123 ) |
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println "Hey " + bean.name |
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assert bean.id == 123 |
给方法传递闭包
闭包也可以像其他对象一样传递给方法:
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def closure = { param -> param + 1 } |
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def answer = [ 1 , 2 ]. collect (closure) |
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assert answer == [ 2 , 3 ] |
上面的代码等价于:
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answer = [ 1 , 2 ]. collect { param -> param + 1 } |
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assert answer == [ 2 , 3 ] |
属性
为了访问属性你可以使用属性名和.:
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def bean = new Expando(name: "James" , location: "London" , id: 123 ) |
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def name = bean.name |
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println ( "Hey ${name}" ) |
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bean.location = "Vegas" |
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println bean.name + " is now in " + bean.location |
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assert bean.location == "Vegas" |
安全导航
如果你在访问属性的时候,避免出现空指针异常的话,那么安全导航操作符可能适合你:
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def foo = null |
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def bar = foo?.something?.myMethod() |
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assert bar == null |
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