Java 使用 lambda 将 Map 格式化为 String
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Using lambda to format Map into String
提问by TEXHIK
I have a map with Integerkeys and values. I need to transform it into a Stringwith this specific format: key1 - val1, key2 - val2, key3 - val3. Now, I'm using forEachto format each element, collect them into a List, and then do String.join();
我有一个带有Integer键和值的地图。我需要将它转换为String具有这种特定格式的：key1 - val1, key2 - val2, key3 - val3. 现在，我使用forEach格式化每个元素，将它们收集到一个列表中，然后执行 String.join();
List<String> ships = new ArrayList<>(4);
for (Map.Entry<Integer, Integer> entry : damagedMap.entrySet())
{
ships.add(entry.getKey() + " - " + entry.getValue());
}
result = String.join(",", ships);
Is there any shorter way to do it? And it would be good to do it with lambda, because I need some practice using lambdas.
有没有更短的方法来做到这一点？用 lambda 来做这件事会很好，因为我需要一些使用 lambda 的练习。
采纳答案by Jon Skeet
I think you're looking for something like this:
我想你正在寻找这样的东西：
import java.util.*;
import java.util.stream.*;
public class Test {
public static void main(String[] args) throws Exception {
Map<Integer, String> map = new HashMap<>();
map.put(1, "foo");
map.put(2, "bar");
map.put(3, "baz");
String result = map.entrySet()
.stream()
.map(entry -> entry.getKey() + " - " + entry.getValue())
.collect(Collectors.joining(", "));
System.out.println(result);
}
}
To go through the bits in turn:
依次浏览这些位：
entrySet()gets an iterable sequence of entriesstream()creates a stream for that iterablemap()converts that stream of entries into a stream of strings of the form "key - value"collect(Collectors.joining(", "))joins all the entries in the stream into a single string, using", "as the separator.Collectors.joiningis a method which returns aCollectorwhich can work on an input sequence of strings, giving a result of a single string.
entrySet()获取一个可迭代的条目序列stream()为该可迭代对象创建一个流map()将该条目流转换为“键-值”形式的字符串流collect(Collectors.joining(", "))将流中的所有条目连接成一个字符串，", "用作分隔符。Collectors.joining是一种返回 a 的方法，Collector它可以处理输入的字符串序列，给出单个字符串的结果。
Note that the order is notguaranteed here, because HashMapisn't ordered. You might want to use TreeMapto get the values in key order.
请注意，这里不保证顺序，因为HashMap不是有序的。您可能希望使用TreeMap来按键顺序获取值。
