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May 2nd, 2009

Binary search arraylist

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Java Syntax (Toggle Plain Text)
	public void deleteDvd(String title)
	{
		String DvdCompare;
		Dvd dvdObj;
		 Collections.sort(dvds);
		for(int i = 0;i< dvds.size();i++)
		{
			DvdCompare = dvds.get(i).getdvdTitle();
			dvdObj = dvds.get(i);
			if(title.equals(DvdCompare))
			{
			System.out.println("Dvd is in system");
			int index =Collections.binarySearch(dvds,DvdCompare);
 
			dvds.remove(index);
			//delete method in arrayList
			}
			else if (!title.equals(DvdCompare))
			{
				System.out.println("Not found Dvd Object");
			}
 
		}
 
 
 
	}
	public void deleteDvd(String title)
	{
		String DvdCompare;
		Dvd dvdObj;
		 Collections.sort(dvds);
		for(int i = 0;i< dvds.size();i++)
		{
			DvdCompare = dvds.get(i).getdvdTitle();
			dvdObj = dvds.get(i);
			if(title.equals(DvdCompare))
			{
			System.out.println("Dvd is in system");
			int index =Collections.binarySearch(dvds,DvdCompare);

			dvds.remove(index);
			//delete method in arrayList
			}
			else if (!title.equals(DvdCompare))
			{
				System.out.println("Not found Dvd Object");
			}

		}
		


	}

I'm tryin to search through my dvds arraylist, find title of dvd and delete it from the arraylist completely.

I have imported
import java.util.Collections;
import java.util.ArrayList;

E:\Java\dvd>javac Inventory.java
Inventory.java:172: cannot find symbol
symbol : method sort(java.util.ArrayList<Dvd>)
location: class java.util.Collections
Collections.sort(dvds);
^
Inventory.java:180: cannot find symbol
symbol : method binarySearch(java.util.ArrayList<Dvd>,java.lang.String)
location: class java.util.Collections
int index = Collections.binarySearch(dvds,DvdC
ompare);

I get this error above and can't seem to figure it out. any ideas please?
^

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Seamus McCarthy

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since Apr 2008

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May 2nd, 2009

Re: Binary search arraylist

For first: why do You call Collections.binarySearch(...), when You already iterate through Your dvd store? If You encounter dvd, that's title equals to searched title, You already have its index ( -> i ), so binarySearch is not needed here.

For second: You'll get "Not found Dvd Object" message every iteration, when current dvd doesn't equals searched dvd.

Regarding to errors:

- "symbol : method sort(java.util.ArrayList<Dvd>)"

I think the problem is, that Your Dvd class doesn't implements Comparable interface, so that method sort, doesn't know which dvd is 'greater' and which is 'lesser'.

- Ad. binarySearch, don't know exactly how does searching by key look like, but propably again - method doesn't know what is the String key You give as argument. ( what if Dvd class has got 2 fields of String type? Which one is the given key? )

Last edited by Zibo; May 2nd, 2009 at 10:16 am.

Zibo

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May 2nd, 2009

Re: Binary search arraylist

Thanks for the help i figured it out, just used dvds.remove(dvdObj); after all and didn't go ahead with the binarySearch method! how would i solve getting not found dvd object every iteration?

Seamus McCarthy

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since Apr 2008

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May 2nd, 2009

Re: Binary search arraylist

You need to check if dvd has been found AFTER You check Your whole dvd store, not during. So it can be for example something like that:

Java Syntax (Toggle Plain Text)
public void deleteDvd(String title)
{
	String DvdCompare;
	Dvd dvdObj;
	Collections.sort(dvds);
 
	boolean found = false;
	for( int i=0 ;i < dvds.size(); i++)
	{
		DvdCompare = dvds.get(i).getdvdTitle();
		dvdObj = dvds.get(i);
		if(title.equals(DvdCompare))
		{
			System.out.println("Dvd is in system");
			dvds.remove(i);
 
			found = true;
 
			break;
		}
	}
 
	if( !found )
		System.out.println("Dvd not found in system");
}
public void deleteDvd(String title)
{
	String DvdCompare;
	Dvd dvdObj;
	Collections.sort(dvds);
	
	boolean found = false;
	for( int i=0 ;i < dvds.size(); i++)
	{
		DvdCompare = dvds.get(i).getdvdTitle();
		dvdObj = dvds.get(i);
		if(title.equals(DvdCompare))
		{
			System.out.println("Dvd is in system");
			dvds.remove(i);
			
			found = true;
					
			break;
		}
	}
	
	if( !found )
		System.out.println("Dvd not found in system");
}

Zibo

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since May 2009

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May 2nd, 2009

Re: Binary search arraylist

Oh rite, ya i get it now, thanks for all your help.

Seamus McCarthy

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