writing and Reading a serialized java object

**KunCode** · 05-20-2012, 05:43 PM

/*hey guys i'm new to java and i have been given an exercise to make a cd collection, write it into a file and read the data back to the program.
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the program is suppose to show you a menu to select from where you can add, delete, view sort, CD's when you add a CD it must be written to a file as an Object and when you want to view CDs or search for a CD the program must read the CD objects from the file they have been written to and must return a cd nam, artist and release date. the code looks like it is writing the Cd to a file but when i try to read (view or search for a cd from the file it gives an error null). so i think i'm note reading the right way.
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thank you for trying to help.
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*/
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import java.util.*;
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public class hipHopCollection {
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ArrayList<cd> list = new ArrayList <cd> ();
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EasyIn ei = new EasyIn();
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private cd invoke;
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private int b;
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public void load()
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{
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System.out.println(" You Entered " + b + " To Add A CD ");
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invoke = new cd();
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System.out.println("Please Enter A CD Name ");
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invoke.setName(ei.readString());
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System.out.println("Please Enter A CD Price");
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invoke.setPrice(ei.readDouble());
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System.out.println("Please Give Ratings For The CD");
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invoke.setRatings(ei.readInt());
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System.out.println("Please Enter A CD release date ");
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invoke.setReleaseDate(ei.readString());
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System.out.println("Please Enter artist Name ");
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invoke.setArtist(ei.readString());
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System.out.println("Please Enter A CD Genre ");
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invoke.setGenre(ei.readString());
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list.add(invoke); // trying to add cd information to invoke.
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}// end of load
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// The following method should return the Object variable invoke that holds the cd INFO
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public Object getInvoke()
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{
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return invoke;
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}
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//.................................................. ......................................
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public int getB()
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{
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return b;
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}
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public void setB()
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{
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b=ei.readInt();
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}
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public void menu(){
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System.out.println(".............................. ........................... ");
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System.out.println("Hi There Please Enter A Number For Your Choice");
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System.out.println(" Pess >>");
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System.out.println("1 >> Add A CD");
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System.out.println("2 >> View List Of CD's");
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System.out.println("3 >> Sort CD's By Price");
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System.out.println("4 >> Search CD By Name");
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System.out.println("5 >> Remove CD(s) By Name");
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System.out.println("0 >> Exit");
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System.out.println(".............................. ...........................");
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System.out.print("Please Enter Chioce >> ");
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}// end of menu
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public void GoodBye()
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{
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System.out.println(" You Entered " + b + " To exit Good_bye" );
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System.exit(0);
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}//end of GoodBye
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public void PriceSort()
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{
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System.out.println(" You Entered " + b + " To Sort CD(s) By price ");
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Collections.sort(list, new SortByPrice());
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for(cd s : list)
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System.out.println(s.getName() + ": " + s.getPrice());
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}// end of PriceSort
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public void NameSearch()
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{
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System.out.println(" You Entered " + b + " To Search CD(s) By Name ");
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System.out.println("Please Enter The Name Of The CD You Are Searching For " );
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String search = ei.readString();
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for(int i=0; i<list.size();i++){
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if(search.equalsIgnoreCase(list.get(i).getName() )){
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System.out.println(list.get(i).getName() + " " + list.get(i).getPrice() + " " + list.get(i).getRatings() + " " + list.get(i).getGenre() );
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}
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}
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}//end of NameSearch
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public void ViewList()
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{
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System.out.println(" You Entered " + b + " To view CD(s) By Name ");
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for(int i=0; i<list.size();i++)
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{
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System.out.println(list.get(i).getName() + " " + list.get(i).getPrice() + " " + list.get(i).getRatings() + " " + list.get(i).getGenre() );
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}
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}// end of ViewList
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public void DeleteCd()
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{
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System.out.println(" You Entered " + b + " To Delete CD(s) By Name ");
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System.out.println("Please Enter The Name Of The CD You Want to Delete ");
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String search = ei.readString();
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for(int i=0; i<list.size();i++)
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{
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if(search.equalsIgnoreCase(list.get(i).getName() ))
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{
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System.out.println(list.get(i).getName());
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list.remove(i);
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}
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}
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}// end of DeleteCD
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//.................................................. ..................................
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public static void main(String[] args) {
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//creating an Instance of EasyIn by object ei. Easy in is a Scanner class for reading
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EasyIn ei = new EasyIn();
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ArrayList<cd> list = new ArrayList <cd> (); // creating an array cd list
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hipHopCollection call = new hipHopCollection();
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ReadWrite rw = new ReadWrite();
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while (true){
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call.menu();
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call.setB();
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//b = ei.readInt();
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if(call.getB()==0)
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{
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call.GoodBye();
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}
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if(call.getB()==1)
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{
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call.load();
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rw.doWriting();// trying to write the cd object to a file
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}
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if(call.getB()==2)
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{
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rw.doReading();// trying to read the cd object from a file
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//call.ViewList();
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}
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if(call.getB()==3)
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{
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call.PriceSort();
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}
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if(call.getB()==4)
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{
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call.NameSearch();
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}
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if(call.getB()==5)
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{
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call.DeleteCd();
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}
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}// end of while
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}// end of main
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}// end of class
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import java.io.Serializable;
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public class cd implements Serializable {
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//creating attributes
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private String cdname = null;
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private double price = 0.0;
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private String artist =null;
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private int ratings =0;
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private String genre=null;
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private String releaseDate =null;
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// creating an Empty constructor
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public cd(){
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}
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public cd (String cdname,double price, int ratings, String genre, String artist, String releaseDate){
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this.cdname=cdname;
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this.price=price;
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this.artist=artist;
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this.ratings=ratings;
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this.genre=genre;
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this.releaseDate=releaseDate;
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}
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public String getGenre(){
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return genre;
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}
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public void setGenre(String genre){
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this.genre =genre;
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}
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public String getArtist(){
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return artist;
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}
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public void setArtist(String artist){
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this.artist=artist;
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}
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public String getName(){
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return cdname;
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}
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public void setName(String cdname){
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this.cdname = cdname;
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}
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public Double getPrice(){
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return price;
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}
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public void setPrice(double price){
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this.price = price;
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}
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public String getReleaseDate(){
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return releaseDate;
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}
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public void setReleaseDate(String releaseDate){
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this.releaseDate = releaseDate;
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}
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public int getRatings(){
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return ratings;
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}
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public void setRatings( int ratings){
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this.ratings = ratings;
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}
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}
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// importing all the packages that we will use
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import java.io.ObjectInputStream;
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import java.io.FileInputStream;
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import java.io.File;
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import java.io.FileNotFoundException;
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import java.io.FileOutputStream;
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import java.io.IOException;
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import java.io.ObjectOutputStream;
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import java.io.OutputStream;
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import java.io.Serializable;
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public class ReadWrite {
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// these are all the attributes
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private String FileName ="CdCollections.dat";
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private OutputStream output;
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private ObjectOutputStream oos;
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private FileOutputStream fos;
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private File file;
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private FileInputStream fis;
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private ObjectInputStream ois;
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//creating an empty constructor
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public ReadWrite()
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{
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// we could initialise all the attributes inside this empty constructor
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}
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//creating a constructor with arguments of a file name.
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public ReadWrite(File file)
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{
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this.file=file;
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try
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{
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//Use a FileOutputStream to send data to a file called CdCollections.dat
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fos = new FileOutputStream(file,true);
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/*
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Use an ObjectOutputStream to send object data to the
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FileOutputStream for writing to disk.
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*/
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oos = new ObjectOutputStream (fos);
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fis=new FileInputStream(file);
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ois = new ObjectInputStream(fis);
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}
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catch(FileNotFoundException e)
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{
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System.out.println("File Not Found");
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}
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catch(IOException a)
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{
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System.out.println(a.getMessage());
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System.out.println("Please check file permissions of if file is not corrupt");
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}
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}// end of the second constructor
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//the following lines of code will be the accessors and mutators
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//.................................................. .................................................. ....
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/**
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* @return the output
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*/
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public OutputStream getOutput() {
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return output;
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}
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/**
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* @param output the output to set
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*/
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public void setOutput(OutputStream output) {
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this.output = output;
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}
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/**
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* @return the objStream
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*/
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public ObjectOutputStream getOos() {
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return oos;
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}
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/**
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* @param objStream the objStream to set
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*/
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public void setObjStream(ObjectOutputStream objStream) {
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this.oos = oos;
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}
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public File getFile() {
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return file;
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}
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public void setFile(File file) {
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this.file = file;
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}
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public FileInputStream getFis() {
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return fis;
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}
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public void setFis(FileInputStream fis) {
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this.fis = fis;
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}
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public ObjectInputStream getOis() {
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return ois;
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}
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public void setOis(ObjectInputStream ois) {
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this.ois = ois;
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}
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// the following lines of code will be the methods for reading and writing
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/*................................................. .......................................
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the following method doWriting will write data from the hipHopCollections source code.
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that will be all the cd information.
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Pass our object to the ObjectOutputStream's
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writeObject() method to cause it to be written out
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to disk.
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obj_out.writeObject (myObject);
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.................................................. ......................................*/
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public void doWriting()
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{
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hipHopCollection call = new hipHopCollection();
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//creating an Object variable hold that will hold cd data from hipHopCollections invoke
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Object hold = call.getInvoke();// THI COULD BE THE PART WHERE I MADE A MISTAKE
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ReadWrite stream = new ReadWrite (new File(FileName));
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try
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{
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/*
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Pass our object to the ObjectOutputStream's
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writeObject() method to cause it to be written out to disk.
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stream.getOos().writeObject(hold);
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*/
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stream.getOos().writeObject(hold);
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stream.getOos().close();
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System.out.println("Done writing Object");
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}
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catch (IOException e)
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{
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System.out.println(e.getMessage());
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System.out.println("Program Failed To Write To The File");
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}
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finally
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{
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System.out.println("The program Has come To An End GoodBye");
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}
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}// end of method DoWriting
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/*................................................. .......................................
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The following method is for reading data from the file written by the above method named
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DoWriting
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.................................................. .......................................*/
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// PLEASE NOT THIS IS THE METHOD THAT GIVES ME NULL EXCEPTION
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public void doReading()
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{
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ReadWrite read = new ReadWrite(new File(FileName));
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try{
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//System.out.println("I AM NOW INSIDE THE TRY TO READ");
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Object obj = read.getOis().readObject();
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System.out.println("tried reading the object");
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cd c = (cd)obj; // trying to cast the object back to cd type
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System.out.println("I have typed cast the Object");
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System.out.println(c.getName());
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System.out.println(c.getGenre());
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System.out.println(c.getArtist());
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System.out.println(c.getPrice());
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System.out.println(c.getRatings());
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System.out.println(c.getReleaseDate());
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read.getOis().close();
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}
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catch(ClassNotFoundException e)
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{
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System.out.println(e.getMessage());
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System.out.println("THE CLASS COULD NOT BE FOUND");
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}
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catch(IOException e)
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{
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System.out.println(e.getMessage());// null
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System.out.println("WE COULD NOT READ THE DATA INSIDE THE FILE");
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}
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}//end of method doReading
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}// end of class ReadWrite