Question

I m new to groovy, and I mread the source of a project gretty

import org.codehaus.jackson.map.ObjectMapper
class JacksonCategory {
static final ObjectMapper mapper = []
    ...
}

我不理解该代码<代码>。 ObjectMappermapper = [], What does [ ] mean here? 我认为这是<条码>,但是如何将其分配给<条码>的。 ObjectMapper?

<>>>>>

取决于。因此,这意味着:

static final ObjectMapper mapper = new ObjectMapper()

但:

String s = []
println s // -> it s `[]` not ``

而且

Integer i = []

放弃例外:

Caught: org.codehaus.groovy.runtime.typehandling.GroovyCastException: Cannot cast object  []  
with class  java.util.ArrayList  to class  java.lang.Integer  
org.codehaus.groovy.runtime.typehandling.GroovyCastException: Cannot cast object  []  with class  
 java.util.ArrayList  to class  java.lang.Integer

Answer 1

它呼吁反对者违约构造者。

http://mrhaki.blogspot.com/2009/09/groovy-goodness-using-lists-and-maps-as.html>

它似乎是<代码>[,总是作为空洞的ArrayList创建的,但在被指定为单独一类的农业ovy 试图进行类胁迫并找到合适的建筑商时。

举动只是把这个方法列入清单,并以此为理由。对于它所研究的物体,有适当数目和类型的论点。

Groovy预计不需要做这样的工作,即延长数量(Integer、BigDecimal等)的java图书馆课程,而是向CastException提供。

实例:

class A {
    String value;
    A() { this("value"); }
    A(String value) { this.value = value; }
}

def A defaultCons = [];
// equivalent to new A()
def A argsCons = ["x"];
// equivalent to new A("x")
def list = [1,2];
// literal ArrayList notation
def String str = [];
// equivalent to str = "[]"

println "A with default constructor: " + defaultCons.value;
println "A with String arg constructo: " + argsCons.value;
println "list: " + list;
println "str: " + str;

友情链接