我试图学习如何在我的日常编程中使用Java 8功能（如lambdas和流），因为它使代码更简洁。
以下是我目前正在处理的内容：我从本地文件中获取字符串流，其中包含一些数据，稍后将转为对象。 输入文件结构看起来像这样：
Airport name; Country; Continent; some number;我的代码如下所示：
public class AirportConsumer implements AirportAPI { List<Airport> airports = new ArrayList<Airport>(); @Override public Stream<Airport> getAirports() { Stream<String> stream = null; try { stream = Files.lines(Paths.get("resources/planes.txt")); stream.forEach(line -> createAirport(line)); } catch (IOException e) { e.printStackTrace(); } return airports.stream(); } public void createAirport(String line) { String airport, country, continent; int length; airport = line.substring(0, line.indexOf(';')).trim(); line = line.replace(airport + ";", ""); country = line.substring(0,line.indexOf(';')).trim(); line = line.replace(country + ";", ""); continent = line.substring(0,line.indexOf(';')).trim(); line = line.replace(continent + ";", ""); length = Integer.parseInt(line.substring(0,line.indexOf(';')).trim()); airports.add(new Airport(airport, country, continent, length)); } }在我的主类中，我遍历对象流并打印出结果：
public class Main { public void toString(Airport t){ System.out.println(t.getName() + " " + t.getContinent()); } public static void main(String[] args) throws IOException { Main m = new Main(); m.whatever(); } private void whatever() throws IOException { AirportAPI k = new AirportConsumer(); Stream<Airport> s; s = k.getAirports(); s.forEach(this::toString); } }我的问题是：我怎样才能优化这段代码，所以我不必分别解析文件中的行，而是从源文件中直接创建一个对象流？ 或者这是我能做到这一点的程度？
I am trying to learn how to utilize Java 8 features(such as lambdas and streams) in my daily programming, since it makes for much cleaner code.
Here's what I am currently working on: I get a string stream from a local file with some data which I turn into objects later. The input file structure looks something like this:
Airport name; Country; Continent; some number;And my code looks like this:
public class AirportConsumer implements AirportAPI { List<Airport> airports = new ArrayList<Airport>(); @Override public Stream<Airport> getAirports() { Stream<String> stream = null; try { stream = Files.lines(Paths.get("resources/planes.txt")); stream.forEach(line -> createAirport(line)); } catch (IOException e) { e.printStackTrace(); } return airports.stream(); } public void createAirport(String line) { String airport, country, continent; int length; airport = line.substring(0, line.indexOf(';')).trim(); line = line.replace(airport + ";", ""); country = line.substring(0,line.indexOf(';')).trim(); line = line.replace(country + ";", ""); continent = line.substring(0,line.indexOf(';')).trim(); line = line.replace(continent + ";", ""); length = Integer.parseInt(line.substring(0,line.indexOf(';')).trim()); airports.add(new Airport(airport, country, continent, length)); } }And in my main class I iterate over the object stream and print out the results:
public class Main { public void toString(Airport t){ System.out.println(t.getName() + " " + t.getContinent()); } public static void main(String[] args) throws IOException { Main m = new Main(); m.whatever(); } private void whatever() throws IOException { AirportAPI k = new AirportConsumer(); Stream<Airport> s; s = k.getAirports(); s.forEach(this::toString); } }My question is this: How can I optimize this code, so I don't have to parse the lines from the file separately, but instead create a stream of objects Airport straight from the source file? Or is this the extent in which I can do this?
最满意答案
您需要使用map()来转换过去的数据。
Files.lines(Paths.get("resources/planes.txt")) .map(line -> createAirport(line));这将返回一个Stream<Airport> - 如果你想返回一个List ，那么你需要在最后使用collect方法。
这种方法也是无状态的，这意味着您不需要实例级别的airports值。
您需要更新您的createAirport方法才能返回某些内容：
public Airport createAirport(String line) { String airport = line.substring(0, line.indexOf(';')).trim(); line = line.replace(airport + ";", ""); String country = line.substring(0,line.indexOf(';')).trim(); line = line.replace(country + ";", ""); String continent = line.substring(0,line.indexOf(';')).trim(); line = line.replace(continent + ";", ""); int length = Integer.parseInt(line.substring(0,line.indexOf(';')).trim()); return new Airport(airport, country, continent, length); }如果您正在寻找更加实用的代码方法，您可能需要考虑重写createAirport以免它改变行。 建筑商对这种事情也很好。
public Airport createAirport(final String line) { final String[] fields = line.split(";"); return new Airport(fields[0].trim(), fields[1].trim(), fields[2].trim(), Integer.parseInt(fields[3].trim())); }把它们放在一起，你的班级现在看起来像这样。
public class AirportConsumer implements AirportAPI { @Override public Stream<Airport> getAirports() { Stream<String> stream = null; try { stream = Files.lines(Paths.get("resources/planes.txt")) .map(line -> createAirport(line)); } catch (IOException e) { stream = Stream.empty(); e.printStackTrace(); } return stream; } private Airport createAirport(final String line) { final String[] fields = line.split(";"); return new Airport(fields[0].trim(), fields[1].trim(), fields[2].trim(), Integer.parseInt(fields[3].trim())); } }You need to use map() to transform the data as it comes past.
Files.lines(Paths.get("resources/planes.txt")) .map(line -> createAirport(line));This will return a Stream<Airport> - if you want to return a List, then you'll need to use the collect method at the end.
This approach is also stateless, which means you won't need the instance-level airports value.
You'll need to update your createAirport method to return something:
public Airport createAirport(String line) { String airport = line.substring(0, line.indexOf(';')).trim(); line = line.replace(airport + ";", ""); String country = line.substring(0,line.indexOf(';')).trim(); line = line.replace(country + ";", ""); String continent = line.substring(0,line.indexOf(';')).trim(); line = line.replace(continent + ";", ""); int length = Integer.parseInt(line.substring(0,line.indexOf(';')).trim()); return new Airport(airport, country, continent, length); }If you're looking for a more functional approach to your code, you may want to consider a rewrite of createAirport so it doesn't mutate line. Builders are also nice for this kind of thing.
public Airport createAirport(final String line) { final String[] fields = line.split(";"); return new Airport(fields[0].trim(), fields[1].trim(), fields[2].trim(), Integer.parseInt(fields[3].trim())); }Throwing it all together, your class now looks like this.
public class AirportConsumer implements AirportAPI { @Override public Stream<Airport> getAirports() { Stream<String> stream = null; try { stream = Files.lines(Paths.get("resources/planes.txt")) .map(line -> createAirport(line)); } catch (IOException e) { stream = Stream.empty(); e.printStackTrace(); } return stream; } private Airport createAirport(final String line) { final String[] fields = line.split(";"); return new Airport(fields[0].trim(), fields[1].trim(), fields[2].trim(), Integer.parseInt(fields[3].trim())); } }更多推荐
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