如何在Jython中使用Java 8 Lambda [英] How to use Java 8 lambdas in Jython

问题描述

我正在尝试在jython中使用java 8流和集合，以查看在纯jython中实现时它们是否有效.在我看来，它可以(对此表示赞赏)

我从一些例子开始，计数

from java.util.function import Function
from java.util import ArrayList
from java.util.stream import Collectors

letters = ArrayList(['a','b','a','c']);

cnt=letters.stream().collect(Collectors.groupingBy(Function.identity(),
                                            Collectors.counting()))

将cnt打印为词典 {u'a':2升，u'b':1升，u'c':1升}

到目前为止，一切都很好.接下来，我找到了一个在java

的流上使用过滤器的示例

List<String>strings = Arrays.asList("abc", "", "bc", "efg", "abcd","", "jkl");
//get count of empty string
int count = strings.stream().filter(string -> string.isEmpty()).count();

这将如何转换为jython.具体来说，如何在jython中编写类似字符串-> sting.isEmpty()之类的Java lambda表达式?

解决方案

以下是在流中使用过滤器的示例，该过滤器需要Predicate(java.util.function.Predicate)类型的对象

对于Java代码:

List<String>strings = Arrays.asList("abc", "", "bc", "efg", "abcd","", "jkl");
//get count of empty string
int count = strings.stream().filter(string -> string.isEmpty()).count();

eqvivalet jython将首先对谓词进行子类化并实现一种测试方法.

from java.util.function import Predicate
from java.util.stream import Collectors

class pred(Predicate):
   def __init__(self,fn):
       self.test=fn

@pred
def mytest(s):
    from java.lang import String
    return not String(s).isEmpty() #or just use len(s.strip())==0

strings = ArrayList(["abc", "", "bc", "efg", "abcd","", "jkl"])
count = strings.stream().filter(mytest).count()
lst=strings.stream().filter(mytest).collect(Collectors.toList())
print(count)
print(lst)

然后打印

计数:

5L

第一:

[abc, bc, efg, abcd, jkl]

I am trying to experiment with java 8 streams and collections in jython to see if they are any efficient then when implemented in pure jython. It occurs to me it could (any comments on this also appreciated)

I started with some examples, the counting

from java.util.function import Function
from java.util import ArrayList
from java.util.stream import Collectors

letters = ArrayList(['a','b','a','c']);

cnt=letters.stream().collect(Collectors.groupingBy(Function.identity(),
                                            Collectors.counting()))

printing cnt as dictionary {u'a': 2L, u'b': 1L, u'c': 1L}

so far so good. Next, I found a example on using filter on streams in java

List<String>strings = Arrays.asList("abc", "", "bc", "efg", "abcd","", "jkl");
//get count of empty string
int count = strings.stream().filter(string -> string.isEmpty()).count();

how would this translate to in jython. specifically how can one write java lambda expression like string -> sting.isEmpty() in jython?

解决方案

here is an example for using a filter on a stream need a object of type Predicate (java.util.function.Predicate)

for java code:

List<String>strings = Arrays.asList("abc", "", "bc", "efg", "abcd","", "jkl");
//get count of empty string
int count = strings.stream().filter(string -> string.isEmpty()).count();

eqvivalet jython would be to first subclassing Predicate and implementing a test method.

from java.util.function import Predicate
from java.util.stream import Collectors

class pred(Predicate):
   def __init__(self,fn):
       self.test=fn

@pred
def mytest(s):
    from java.lang import String
    return not String(s).isEmpty() #or just use len(s.strip())==0

strings = ArrayList(["abc", "", "bc", "efg", "abcd","", "jkl"])
count = strings.stream().filter(mytest).count()
lst=strings.stream().filter(mytest).collect(Collectors.toList())
print(count)
print(lst)

then prints

count:

5L

lst:

[abc, bc, efg, abcd, jkl]

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