save and load

[keiriso samaron]

Hello there,
I need help with the following code. I would like to add a method that will save items and load them when the program is rerun.

import java.util.ArrayList;
public class Library
{
	
	
	// Properties: ArrayList to store contents of Item class
	ArrayList<Manual> items;// Collection of items
	ArrayList<String> keys;

	// Constructor
	public Library()
	{
		// new container to hold items from Item class
		items = new ArrayList<Manual>(); 
		keys = new ArrayList<String>();
	}

	// method to return size of ArrayList
	public int getSize()
	{
		// return total number of items contained in ArrayList
		return items.size(); 
	}
	//add method 
	public void add(Manual anItem)
	{
		items.add(anItem); // add anItem to items
		keys.add(anItem.getRefNo());
	}

	// print each item from the Items container class
	public void print(String heading)
	{
		System.out.println(heading);
		for (int i=0; i < items.size(); i++) // for each item in ArrayList
			System.out.println( items.get(i) ); // get it and print it
	}

	//find method
	public Manual find(String refNo) 
	{
		int index = keys.indexOf(refNo);
		if(index==-1) //if item not found
			return null;
		else
			return items.get(index);
	}

[Tushar Goel]

So what is your problem? Have you struck somewhere? What is your question??

[Knute Snortum]

Welcome to the Ranch!

Can you show us what you've tried so far?

[Liutauras Vilda]

Before you specify exact problems you are facing, there are some other issues needs to be fixed.

1. Fields are not private (items, keys). They really should be.
2. Methods names are poorly chosen and not self explaining.
3. Comments are added in addition to explain what methods suppose to do, unfortunately these are not descriptive too and there are too many of them.

Try to come up with self explaining method names, so you wouldn't need current comments.

[keiriso samaron]

Hello there,

Thank you for your quick response. I am trying to program a library application. I have three classes, a Manual class that hold item, a Library class that hold items and Menu class with a switch cases. What I am trying to achieve is to be able to have a switch case that will save the items. So, I need to have a method that will save items. Please see three classes under:

public class Manual 

{
	String refNo;
	String name;
	int price; // in pence

	//Default Constructor
		public Manual()
		{
			set("000000","No name",0);
			/*refNo = "000000";
			name = "No Name";
			price = 0;*/
			
		}
	//Constructor with parameters
		public Manual (String refNo,String name,int price)
		{
			set(refNo,name,price); //use of set method
			/*this.refNo = refNo;
			this.name = name;
			this.price = price;*/
		}
	//set method for all fields 
	public void set(String refNo, String name,int price)
	{
		this.refNo = refNo;
		this.name = name;
		this.price = price;
	}
	//set method for individual fields
	public void setRefNo(String refNo)
	{
		this.refNo = refNo;
	}
	public void setName(String name)
	{
		this.name = name;
	}
	public void setPrice(int price)
	{
		this.price = price;
	}
	//get method for individual fields
	public String getRefNo()
	{
		return refNo;
	}
	public String getName()
	{
		return name;
	}
	public int getPrice()
	{
		return price;
	}
	//ask method for user input
	public void ask(String prompt)
	{
		System.out.println(prompt);
		String refNo = Console.askString("refNo: ");
		setRefNo(refNo);
		setName(Console.askString("name: "));
		setPrice(Console.askInt("price: "));
		
	}
	//Print method
	public void print()
	{
		System.out.println("\nrefNo: "+ refNo );
		System.out.println("name: "+name);
		System.out.println("price: "+price);
	}
	//toString method
	   public String toString()
	   {
		   return refNo+" "+name+" "+price;
	   }
	
	//
	   public String askRefNo(String prompt) {
		String refNo = Console.askString("Enter refNo: ");
		return refNo;
	}
}

import java.util.ArrayList;
public class Library
{
	
	
	// Properties: ArrayList to store contents of Item class
	ArrayList<Manual> items;// Collection of items
	ArrayList<String> keys;

	// Constructor
	public Library()
	{
		// new container to hold items from Item class
		items = new ArrayList<Manual>(); 
		keys = new ArrayList<String>();
	}

	// method to return size of ArrayList
	public int getSize()
	{
		// return total number of items contained in ArrayList
		return items.size(); 
	}
	//add method 
	public void add(Manual anItem)
	{
		items.add(anItem); // add anItem to items
		keys.add(anItem.getRefNo());
	}

	// print each item from the Items container class
	public void print(String heading)
	{
		System.out.println(heading);
		for (int i=0; i < items.size(); i++) // for each item in ArrayList
			System.out.println( items.get(i) ); // get it and print it
	}

	//find method
	public Manual find(String refNo) 
	{
		int index = keys.indexOf(refNo);
		if(index==-1) //if item not found
			return null;
		else
			return items.get(index);
	}

public class LibraryMenu 
{
	
	public static void main(String[]args)

	{
		//Develop menu-driven application
		Library items = new Library();
		Manual item;

		boolean finished = false; // not finished
		char option;
		while(! finished) // not finished
		{
			option = Console.askOption("Select A)dd, F)ind,L)oad,P)rint,Q)uit,S)ave");
			switch (option)

			{
			case 'A':
				item = new Manual();
				item.ask("Enter item details: ");
				if (items.find(item.getRefNo()) != null)
				{
					System.out.println("Item already exists");
				}
				else
				{
					items.add(item);
				}
				break;
			case 'F':
				item = new Manual();
				String itemRefNo = item.askRefNo("\nEnter refNo for item: ");
				// check to see if item already in container
				if ( items.find( itemRefNo) != null )
					System.out.println("Item found is: " +items.find(itemRefNo));
				else
					System.out.println("Error: Item not found \n");

				break;
			case 'L':
				//Save.loadScript(itemRefNo);
				break;
			case 'P':
				items.print("Items are: ");
				break;
			case 'S':
			//Save.saveAndQuit();
				break;
			case 'Q':
				finished = true;  // finished
				System.out.println("End of application");
				break;
			default:
				System.out.println("Invalid option!");
			}

		}


	}
}

[Carey Brown]

I would change

Library items = new Library();

to

Library library = new Library();

Then your load would be

library = Library.load(); // a new static method

and save would be

library.save(); // a new method

Load and save would probably be best done using serialization. Give it a try.
Alternatively you could use a flat file with each line containing a Manual with it's fields separated by some delimiter.

[keiriso samaron]

Thanks for your response. I need some help with writing of the methods. I will appreciate if you could give a example.

[keiriso samaron]

I am trying to use this method but don't know to relate to my Library class.

public void loadScript(String refNo) {
		// TODO Auto-generated method stub
		FileInputStream fis = null;
		ObjectInputStream in = null;
		File file = new File(refNo + ".ser");
		if (file.exists()) {
			try {
				fis = new FileInputStream(file);
				in = new ObjectInputStream(fis);
				lib = (Library) in.readObject();
				fis.close();
				in.close();

			} catch (IOException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			} catch (ClassNotFoundException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}

		} else {
			System.out.println("\nThe file does not exist!");
		}
	}

[Carey Brown]

Why "loadScript" and not just "load"?

Why load a specific refNo? Why not load all of them as a Library.

Likewise, save the entire library as a whole.

What is a 'lib'?

Why cast to a Library when it appears that you're reading a Manual of a given refNo?

[Carey Brown]

Your Library class needs two new methods: load(), and save(). Both of which should not need any arguments.

[keiriso samaron]

Thanks Carey,
I don't understand what you mean with no argument. Do I need to create the methods as follow:

public void load()
{
	
}
public void save(){
	
}

[Carey Brown]

Methods inside Library

    public void save()
    {
    	
    }
    
    public static Library load()
    {
    	  
    }

[keiriso samaron]

I added the two methods in Library, and created the options but not getting the results when saving and loading.

[Carey Brown]

What did you put in the body of those two methods?
How are you calling them?

[keiriso samaron]

I put the following arguments:
Please bear in mind, I am in a first java programming course.

public static Library load()
{
		FileInputStream fis = null;
		ObjectInputStream in = null;
		File file = new File(name + ".ser");
		if (file.exists()) {
			try {
				fis = new FileInputStream(file);
				in = new ObjectInputStream(fis);
				Library= (Library) in.readObject();
				//fis.close();
				//in.close();

			} catch (IOException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			} catch (ClassNotFoundException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}

		} else {
			System.out.println("\nThe file does not exist!");
		}
	
	
	
}

	public static void save()
{
	String fileName = Console.askString("Enter a file name:");
	FileOutputStream fos = null;
	ObjectOutputStream out = null;
	try {
		fos = new FileOutputStream(fileName);
		out = new ObjectOutputStream(fos);
		out.writeObject(Library);
		//fos.close();
		//out.close();
	} catch (FileNotFoundException e) {
		// TODO Auto-generated catch block
		e.printStackTrace();
	} catch (IOException e) {
		// TODO Auto-generated catch block
		e.printStackTrace();
	}
	

[Carey Brown]

keiriso samaron wrote:I put the following arguments:
Please bear in mind, I am in a first java programming course.

public static Library load()
{
		FileInputStream fis = null;
		ObjectInputStream in = null;
		File file = new File(name + ".ser"); //### w
		if (file.exists()) {
			try {
				fis = new FileInputStream(file);
				in = new ObjectInputStream(fis);
				Library= (Library) in.readObject(); //### this is missing a variable name
				//fis.close(); //### you don't need this
				//in.close(); //### you need this
                                //### the variable is not being returned 
			} catch (IOException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			} catch (ClassNotFoundException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}

		} else {
			System.out.println("\nThe file does not exist!");
		}
	
	
	
}

	public static void save() //### NOT static
{
	String fileName = Console.askString("Enter a file name:");
	FileOutputStream fos = null;
	ObjectOutputStream out = null;
	try {
		fos = new FileOutputStream(fileName);
		out = new ObjectOutputStream(fos);
		out.writeObject(Library); //### change Library to 'this'
		//fos.close(); //### don't need this
		//out.close(); //### do need this
	} catch (FileNotFoundException e) {
		// TODO Auto-generated catch block
		e.printStackTrace();
	} catch (IOException e) {
		// TODO Auto-generated catch block
		e.printStackTrace();
	}
	

See comments I added in above code.
Both Library and Manual will need to 'implement' Serializable, as well as provide

private static final long serialVersionUID = 42L;

For now I'd just hard code a file name.