Given a, b two files, each storing 5 billion url, url each accounted for 64 bytes each, the memory limit is 4G, let you find out a, common url b file?

package com.hadoop.hdfs;

import org.apache.hadoop.yarn.webapp.hamlet.Hamlet;
import org.junit.Test;

import java.io.*;
import java.util.HashMap;
import java.util.HashSet;

public class Suanfa1 {
    @Test
    public void a1() throws IOException {
        BufferedReader bufferedReader = new BufferedReader(new FileReader("D:/aa.txt"));
//        BufferedWriter bufferedWriter = new BufferedWriter(new FileWriter("D://"))
        String str1 = "";
        while ((str1 = bufferedReader.readLine())!=null){
            int i = (int) (hashCode(str1)%1000);
            BufferedWriter bufferedWriter = new BufferedWriter(new FileWriter("D://aa"+String.valueOf(i)+".txt"));
            bufferedWriter.write(str1);
            bufferedWriter.close();
            System.out.println(i);
        }
        bufferedReader.close();
    }

    public void a2() throws IOException {
        BufferedReader bufferedReader = new BufferedReader(new FileReader("D:/bb.txt"));
//        BufferedWriter bufferedWriter = new BufferedWriter(new FileWriter("D://"))
        String str1 = "";
        while ((str1 = bufferedReader.readLine())!=null){
            int i = (int) (hashCode(str1)%1000);
            BufferedWriter bufferedWriter = new BufferedWriter(new FileWriter("D://bb"+String.valueOf(i)+".txt"));
            bufferedWriter.write(str1);
            bufferedWriter.close();
        }
        bufferedReader.close();
    }

    public long hashCode(String str) {
        long h = 0;
        if (h == 0) {
            int off = 0;
            char val[] = str.toCharArray();
            long len = str.length();
            for (long i = 0; i < len; i++) {
                h = 31 * h + val[off++];
            }
        }
        return h;
    }

    @Test
    public void a3() throws IOException {
        ? 1 ();
        a2 ();
        for (int i = 0; i < 1000; i++) {
            BufferedReader bufferedReader1 = new BufferedReader(new FileReader("D://aa"+String.valueOf(i)+".txt"));
            BufferedReader bufferedReader2 = new BufferedReader(new FileReader("D://bb"+String.valueOf(i)+".txt"));
            HashSet set = new HashSet();
            String input1 = "";
            while ((input1 = bufferedReader1.readLine())!=null){
                set.add(hashCode(bufferedReader1.readLine()));
            }

            String input2 = "";
            while ((input2 = bufferedReader2.readLine())!=null){
                if (set.contains(hashCode(input2))){
                    System.out.println(input2);
                }
            }
        }

    }
}