EzDevInfo.com

When to use LinkedList over ArrayList?

I've always been one to simply use:

List<String> names = new ArrayList<String>();

I use the interface as the type name for portability, so that when I ask questions such as these I can rework my code.

When should LinkedList be used over ArrayList and vice-versa?

Initialization of an ArrayList in one line

I want to create a list of options for testing purposes. At first, I did this:

ArrayList<String> places = new ArrayList<String>();
places.add("Buenos Aires");
places.add("Córdoba");
places.add("La Plata");

Then I refactored the code as follows:

ArrayList<String> places = new ArrayList<String>(
    Arrays.asList("Buenos Aires", "Córdoba", "La Plata"));

Is there a better way to do this?

What are the differences between ArrayList and Vector?

What are the differences between these two data structures and where should you use each of them?

What is the difference between ArrayList.clear() and ArrayList.removeAll()?

Assuming that arraylist is defined as ArrayList<String> arraylist, is arraylist.removeAll(arraylist) equivalent to arraylist.clear()?

If so, can I assume that the clear() method is more efficient for emptying the array list?

Are there any caveats in using arraylist.removeAll(arraylist) instead of arraylist.clear()?

java arraylist copy

I have a ArrayList l1 of size 10. I assign l1 to new list reference type l2. Will l1 and l2 point to same arraylist object? Or a copy of arraylist object is assigned to l2. Because Using l2 reference, if I update the list object, it reflects the changes in l1 reference type also.

eg.

List<Integer> l1 = new ArrayList<Integer>();
for(int i=1;i<=10;i++)
   l1.add(i);
List l2 = l1;
l2.clear();

Is there no other way to assign a copy of list object to new reference variable, apart from creating 2 list objects, and doing copy on collections from old to new?

Thanks in advance

Get specific ArrayList item

public static ArrayList mainList = someList;

How can I get a specific item from this ArrayList? mainList[3]?

Java: how can I split an ArrayList in multiple small ArrayLists?

How can I split an ArrayList (size=1000) in multiple ArrayLists of the same size (=10) ?

ArrayList<Integer> results;

How to count the number of occurrences of an element in a List

I have an ArrayList, a Collection class of Java, as follows:

ArrayList<String> animals = new ArrayList<String>();
animals.add("bat");
animals.add("owl");
animals.add("bat");
animals.add("bat");

As you can see, the animals ArrayList consists of 3 bat elements and one owl element. I was wondering if there is any API in the Collection framework that returns the number of bat occurrences or if there is another way to determine the number of occurrences.

I found that Google's Collection Multiset does have an API that returns the total number of occurrences of an element. But that is compatible only with JDK 1.5. Our product is currently in JDK 1.6, so I cannot use it.

How to avoid "ConcurrentModificationException" while removing elements from `ArrayList` while iterating it? [duplicate]

I'm trying to remove some elements from ArrayList while iterating it like this:

for (String str : myArrayList) {
        if (someCondition) {
            myArrayList.remove(str);
        }
}

Of course, I get ConcurrentModificationException when trying to remove item from the list at the same time when iterating myArrayList. Is there some simple solution to do that right?

How to sort an ArrayList in Java [duplicate]

i have a class named Fruit i creating a list of this class and add each fruit in each objects i want to sort this list based on the order of name

public class Fruit{

    private String fruitName;
    private String fruitDesc;
    private int quantity;

    public String getFruitName() {
        return fruitName;
    }
    public void setFruitName(String fruitName) {
        this.fruitName = fruitName;
    }
    public String getFruitDesc() {
        return fruitDesc;
    }
    public void setFruitDesc(String fruitDesc) {
        this.fruitDesc = fruitDesc;
    }
    public int getQuantity() {
        return quantity;
    }
    public void setQuantity(int quantity) {
        this.quantity = quantity;
    }
}

and i create its list using for loop

List<Fruit>  fruits= new ArrayList<Fruit>();

Fruit fruit;
for(int i=0;i<100;i++)
{
   fruit = new fruit();
   fruit.setname(...);
   fruits.add(fruit);
}

and i need to sort this arraylist using the fruit name in each objet in the list

how??

Convert Iterator to ArrayList

Given Iterator<Element>, how can we convert that iterator to ArrayList<Element> (or List<Element>) in the best and fastest way possible, so that we can use ArrayList's operations on it such as get(index), add(element), etc.

make arrayList.toArray() return more specific types

So, normally ArrayList.toArray() would return a type of Object[]....but supposed it's an Arraylist of object Custom, how do I make toArray() to return a type of Custom[] rather than Object[]?

How to remove all null elements from a ArrayList or String Array?

I try with a loop like that

// ArrayList tourists

for (Tourist t : tourists) {
    if (t != null) {     
        t.setId(idForm); 
    }   
}

But it isn't nice. Can anyone suggest me a better solution?

Some useful benchmarks to make better decision:

While loop, For loop and Iterator Performance Test

ArrayIndexOutOfBoundsException when iterating through an ArrayList

Right now, I have a program containing a piece of code that looks like this:

while (arrayList.iterator().hasNext()) {
     //value is equal to a String value
     if( arrayList.iterator().next().equals(value)) {
          // do something 
     }
}

Am I doing that right, as far as iterating through the ArrayList goes?

The error I am getting is:

java.lang.ArrayIndexOutOfBoundsException: -1
    at java.util.ArrayList.get(Unknown Source)
    at main1.endElement(main1.java:244)
    at com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.endElement(Unknown Source)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanEndElement(Unknown Source)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl$FragmentContentDriver.next(Unknown Source)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl.next(Unknown Source)
    at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanDocument(Unknown Source)
    at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(Unknown Source)
    at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(Unknown Source)
    at com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(Unknown Source)
    at com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.parse(Unknown Source)
    at com.sun.org.apache.xerces.internal.jaxp.SAXParserImpl$JAXPSAXParser.parse(Unknown Source)
    at javax.xml.parsers.SAXParser.parse(Unknown Source)
    at javax.xml.parsers.SAXParser.parse(Unknown Source)
    at main1.traverse(main1.java:73)
    at main1.traverse(main1.java:102)
    at main1.traverse(main1.java:102)
    at main1.main(main1.java:404)

I would show the rest of the code, but it's pretty extensive, and if I am not doing the iteration correctly, I would assume the only possibility is that I am not initializing the ArrayList properly.

How to randomize ArrayList?

I have two arraylist filelist and imgList which related to each other, e.g. "H1.txt" related to "e1.jpg". How to automatically randomized the list of imgList according to the randomization of fileList? Like in excel, if we sort certain column, the other column will automatically follow?

String [] file = {"H1.txt","H2.txt","H3.txt","M4.txt","M5.txt","M6.txt"};
ArrayList<String> fileList = new ArrayList<String>(Arrays.asList(file));

String [] img = {"e1.jpg","e2.jpg","e3.jpg","e4.jpg","e5.jpg","e6.jpg"};
ArrayList<String> imgList = new ArrayList<String>(Arrays.asList(img));

//randomized files
Collections.shuffle(fileList);

output after randomization e.g.:

fileList = {"M4.txt","M6.txt","H3.txt","M5.txt","H2.txt","H1.txt"};

intended output:

 imgList = {"e4.jpg","e6.jpg","e3.jpg","e5.jpg","e2.jpg","e1.jpg"};