迭代地图常规时更新地图中的值 [英] Updating value in a map while iterating the map groovy

问题描述

我是Groovy的新手，但无法通过网络找到我的问题的答案.我有一个非常简单的地图: Map< String，Object> .我需要在迭代时使用一种方法来更新此地图的值.我找到了一种方法:

I'm very new to Groovy but I couldn't find an answer to my question over web. I've a very simple map: Map<String, Object>. I need to update values of this map using a method while iterating. I've found a way to do it:

Map<String, Object> newMap = myMap.each { it -> it.value = getValue(it.key) }

我不明白为什么这行不通:

I couldn't understand why this doesn't work:

Map<String, Object> newMap = myMap.each { k,v -> v = getValue(k) }

谢谢.

推荐答案

如果您了解Java，则可以将下面的代码粗略地理解为Groovy所做的事情.确保检查 eachBlock 中有关分配给 v

If you know Java, then consider the code below as an crude approximation to what Groovy is doing. Be sure to examine the comment in the eachBlock regarding assignment to v

import java.util.*;

public class Mapper {

    public void each(Map<String,Object> map) {
        for (String k : map.keySet()) {
            Object v = map.get(k);
            eachBlock(k,v);
        }
    }

    public void eachBlock(String k, Object v) {
        System.out.println("k: " + k + " , v: " + v);
        // assigning to v here is local, on the stack:
        // v = new Integer(22);
    }

    public static void main(String... args) {
        Map<String,Object> map = new HashMap<String,Object>();
        map.put("abc", new Integer(99));
        map.put("def", new Double(3.14d));
        map.put("ijk", new ArrayList());

        Mapper mapper = new Mapper();
        mapper.each(map);
    }
}

这篇关于迭代地图常规时更新地图中的值的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！