Storage.java

import java.io.BufferedWriter;
import java.io.BufferedReader;
import java.io.FileWriter;
import java.io.FileReader;
import java.io.IOException;
import java.util.Scanner;

public class storage{
    public class record{
        String key;
        String val;

        record(String key_, String val_){
            key = key_;
            val = val_;
        }
    }

    public static String hashing(String key){
        int hash = 7;
        for (int i = 0; i < key.length(); i++) {
            hash = (hash*31 + key.charAt(i))%1000000;
        }
        return Integer.toString(hash);

    }
    public static String get(String key_){
        String target_line = "# key_start:"+hashing(key_);
        BufferedReader br = null;
        FileReader fr = null;
        String val = "";

        try {

            fr = new FileReader("data.txt");
            br = new BufferedReader(fr);

            String sCurrentLine;

            br = new BufferedReader(new FileReader("data.txt"));

            while ((sCurrentLine = br.readLine()) != null) {
                if (sCurrentLine.equals(target_line)) {
                    String tmp = "";
                    sCurrentLine = br.readLine();
                    while (!sCurrentLine.equals("# key_end:")) {
                        tmp += sCurrentLine;
                        sCurrentLine = br.readLine();
                    }

                    if (!tmp.equals(key_))
                        continue;
                    sCurrentLine = br.readLine();
                    sCurrentLine = br.readLine();
                    while (!sCurrentLine.equals("# val_end:")) {
                        val += sCurrentLine;
                        sCurrentLine = br.readLine();
                    }
                    return val;
                }

            }
        }
            catch(IOException e){
                e.printStackTrace();
                System.out.println(e);
            }

        System.out.println("key not founded");
        return "failed";
    }

    public static String insert(String key_, String val_){

        String hash_string = hashing(key_);
        try {
            FileWriter writer = new FileWriter("data.txt", true);
            writer.write("# key_start:"+hash_string+"\n");
            writer.write(key_);
            writer.write("\n# key_end:\n");
            writer.write("# val_start:\n");
            writer.write(val_);
            writer.write("\n# val_end:\n");
            writer.close();
        } catch (IOException e) {
            e.printStackTrace();
            System.out.println(e);
            return "False";
        }
        return "True";
    }


    public static void main(String []args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print(">(type quit for key or value to quit)\n");
        System.out.print(">insert a key:");
        String key = scanner.nextLine();
        System.out.print(">insert a val:");
        String value = scanner.nextLine();

        while (!value.equals("quit") && !key.equals("quit")){
            insert(key,value);
            System.out.print(">insert a key:");
            key = scanner.nextLine();
            System.out.print(">insert a val:");
            value = scanner.nextLine();
        }
        System.out.print("type a key to get a value back or type quit to quit:");
        key = scanner.nextLine();

        while (!key.equals("quit")){
            String tmp = get(key);
            if (!tmp.equals("failed")) {
                System.out.println("key:" + key + "\n");
                System.out.println("val:" + tmp + "\n");
            }
            System.out.print("type a key to get a value back or type quit to quit:");
            key = scanner.nextLine();
        }
    }


}


/*  Sample output 
 key_start:314616
key
# key_end:
# val_start:
valeu
# val_end:
# key_start:257227
123
# key_end:
# val_start:
456
# val_end:
# key_start:249

# key_end:
# val_start:
'
# val_end:
# key_start:857550
null
# key_end:
# val_start:
null
# val_end:
# key_start:752597
keey
# key_end:
# val_start:
valeu
# val_end:
*/

Overall looks good and working. But there are a few points I wanted to mention to @bryan

• LINE27/73, for both function return type, you can use boolean

• implement inserts

• adding timestamp (I suggest to store in long type, ref https://www.tutorialspoint.com/java/util/date_gettime.htm since we need to use FIFO strategy

• adding frequency since we need to use LFU strategy

• I found out you never use your record classes, Do you really needed it? Also btw the java convention will capitalize the 1st letter for class name so if you are keeping it, could you rename to Record?

Let me know if you have any more problems :) Keep it on!