Java 8 "Missing return type"lambda 表达式错误

Question

我是 Java 8 的新手，正在尝试理解这些概念。我正在得到

Missing return type

我传递给 ReadTheFile 方法的 Lambda 表达式出现错误。

BufferReaderProcessor

package java8.programs;

import java.io.BufferedReader;
import java.io.IOException;

@FunctionalInterface
public interface BufferReadderProcessor {
    String process(BufferedReader br) throws IOException;
}

MainJava

package java8.programs;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;

public class MainJava {
    public static void main(String[] args) throws IOException {
        MainJava obj = new MainJava();

        String message = obj.ReadTheFIle((BufferedReader br) -> {
                while (br.readLine()!=null)
                    br.readLine();
        });
        System.out.println(message);
    }

    public String ReadTheFIle(BufferReadderProcessor bp) throws IOException {
        BufferedReader br = new BufferedReader(new FileReader(new File("G:\\DemoJavaFile.txt")));

        return bp.process(br);
    }
}

Answer 1

您的 lambda 表达式实现了 BufferReaderProcessor 的 String process(BufferedReader br) 方法，因此它应该返回一个 String。

例如，假设您希望返回从 BufferedReader 读取的数据:

    String message = obj.ReadTheFIle((BufferedReader br) -> {
        StringBuilder sb = new StringBuilder();
        String line = br.readLine();
        while (line != null) {
            sb.append(line);
            line = br.readLine();
        }
        return sb.toString();
    });