Using closures and collections in Groovy 1.0

1. Closure Package

Closures are a handy feature provided by many dynamic languages, something like an inner class in Java, except that there is only one method in the closure, but this method can have any number of arguments.

Java code

This code will output "Hello World".

1. def closure = { param -> println("hello ${param}") }
2. closure.call("world!")

The closure package "{}" is enclosed, "->" is preceded by a parameter, followed by a processing statement, can be invoked using call, or it can be executed directly after "{}" by using "()".

Closures can have more than one parameter, and each parameter is separated by ",". If there is only one argument can be omitted without writing, you can use the keyword "it" to represent.

We can write the above example as follows:

Java code

closure = { println("hello ${it}") }('world')

Or

Java code

1. closure = { param1,param2->　
2.　　　　 println(param1+param2) }('hello ','world')

Several of the above are written out "Hello World".

2. Collection

(1) List

Java code

1. def list = [1, 2, 'hello', new java.util.Date()]
2. assert list.size() == 4　
3. assert list[1]==2　
4. assert list.get(2) == 'hello'

(2) Map

Java code

1. def map = ['name':'James', 'location':'London']
2. assert map.size() == 2　
3. assert map.get('name') == 'James'
4. assert map['location']=='London'

(3) Circulation

Java code

1. def list = [1, 2, 3]
2. for (i in list) {
3.　　 print i
4. }
5. println()
6.
7. list.each{item->　
8.　　 print item　
9. }
10. println()
11.
12. ['name':'yanhua','addr':'beijing'].each{println it}
13. ['name':'yanhua','addr':'beijing'].each{key,value->println "${key} ^_^ ${value}"}

The results of the above operation are as follows:

123

123

Name=yanhua

Addr=beijing

Name ^_^ Yanhua

Addr ^_^ Beijing