使用函数式接口来传递行为

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

@FunctionalInterface
public interface BufferedReaderProcessor {
    String process(BufferedReader b) throws IOException;
}

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

public class ProcessFile {
    //读取一行数据
    public static String processFile() throws IOException{
        try(BufferedReader br = new BufferedReader(new FileReader("data.txt"))){
            return br.readLine();
        }
    }
    //如果想读多行，使用函数式接口来传递行为
    public static String processFile(BufferedReaderProcessor p) throws IOException{
        try(BufferedReader br = new BufferedReader(new FileReader("data.txt"))){
            return p.process(br);//执行一个行为
        }
    }
    public static void main(String[] args) throws IOException {
        System.out.println(processFile());
        String oneLines = processFile((BufferedReader br)->br.readLine());//传递Lambda
        System.out.println(oneLines);
        String twoLines = processFile((BufferedReader br)->br.readLine()+" "+br.readLine());
        System.out.println(twoLines);
    }
}