DependencyInversionPrinciple.java

package com.insightfullogic.java8.examples.chapter8;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.Reader;
import java.util.List;
import java.util.function.Function;
import java.util.stream.Stream;

import static java.util.stream.Collectors.toList;

public class DependencyInversionPrinciple {

    public static interface HeadingFinder {
        public List<String> findHeadings(Reader reader);
    }

    public static class NoDIP implements HeadingFinder {
        // BEGIN nodip_headings
public List<String> findHeadings(Reader input) {
    try (BufferedReader reader = new BufferedReader(input)) {
        return reader.lines()
                     .filter(line -> line.endsWith(":"))
                     .map(line -> line.substring(0, line.length() - 1))
                     .collect(toList());
    } catch (IOException e) {
        throw new HeadingLookupException(e);
    }
}
        // END nodip_headings
    }

    public static class ExtractedDIP implements HeadingFinder {
        // BEGIN refactored_headings
public List<String> findHeadings(Reader input) {
    return withLinesOf(input,
                       lines -> lines.filter(line -> line.endsWith(":"))
                                     .map(line -> line.substring(0, line.length()-1))
                                     .collect(toList()),
                       HeadingLookupException::new);
}
        // END refactored_headings

        // BEGIN with_lines_Of
private <T> T withLinesOf(Reader input,
                          Function<Stream<String>, T> handler,
                          Function<IOException, RuntimeException> error) {

    try (BufferedReader reader = new BufferedReader(input)) {
        return handler.apply(reader.lines());
    } catch (IOException e) {
        throw error.apply(e);
    }
}
        // END with_lines_Of
    }

}