デザインパターン「Adapter」 ref: http://qiita.com/shoheiyokoyama/items/bd1c692db480b640c976

file.tex

Apple=iPod

FileIo.java

import java.io.*;

public interface FileIo {
    public void readFromFile(String filename) throws IOException;
    public void writeToFile(String filename) throws IOException;
    public void setValue(String key, String value);
    public String getValue(String key);
}

FileProperties.js

import java.util.*;
import java.io.*;

public class FileProperties extends Properties implements FileIo {
    public void readFromFile(String filename) throws IOException {
        load(new FileInputStream(filename));
    }

    public void writeToFile(String filename) throws IOException {
        store(new FileOutputStream(filename), "Written by FileProperties");
    }

    public void setValue(String key, String value) {
        setProperty(key, value);
    }

    public String getValue(String key) {
        return getProperty(key, "");
    }
}

Main.java

public static void main(String[] args) {
        FileIo fileIo = new FileProperties();//※
        try {
            fileIo.readFromFile("file.txt");
            fileIo.setValue("Apple", "iPhone");
            fileIo.setValue("Google", "Android");
            fileIo.setValue("Git", "Hub");
            fileIo.setValue("DesignPattern", "Adapter");
            fileIo.writeToFile("newfile.txt");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

newfile.tex

#Written by FileProperties
#Sun Feb 07 20:49:50 JST 2016
DesignPattern=Adapter
Apple=iPhone
Git=Hub
Google=Android