How to fill list java

Ways to fill a list in Java

If you’re not really «filling», but returning object state of some kind, just have the given method build the List and return it. A method like is appropriate in situations like the following: The method you’re writing doesn’t want to care about where the list came from.

Ways to fill a list in Java

Why not follow the Java API’s Collections class and make your fill methods static (if it makes sense and is independent of object state).

MyListFiller.fill( myList, args ); 

At any rate, creating a filler interface makes sense if the fill method plans to change. If you’re not really «filling», but returning object state of some kind, just have the given method build the List and return it.

It depends on the situation.

A method like getSnapList() is appropriate in situations like the following:

1. The method you’re writing doesn’t want to care about where the list came from.
2. The method shouldn’t know what kind of list it’s getting — for example, if you want to change to using a LinkedList , then you can do it in getSnapList() instead of all the methods that call fillSnapList() .
3. You will only ever want to fill new lists.

A method like fillSnapList() is appropriate in situations like the following:

1. You may want to fill the list more than one time.
2. You may want to vary the way the list is filled (i.e. what gets put into it).
3. You need to fill a list that someone else hands you.
4. You need to share the list among more than one class or object, and you might need to refill it at some point in its lifespan.

I like approach 1 better than approach 2, because the list is really the output of the method that you’re calling. Approach 1 makes that more clear than approach 2.

Also, approach 1 gives the method the opportunity to return an unmodifyable list. You might want this if the list should be filled once and shouldn’t be modified later.

Java is not a functional programming language, but the first approach is more in the functional programming style than the second approach (in functional programming, immutability and avoiding mutable state are important ideas — and one important advantage of those is that they make concurrent programming easier, which is also useful in a non-functional programming language).

Java — Fill a list with objects from existing list object with, Connect and share knowledge within a single location that is structured and easy to search. I have a list of objects which i want to iterate and for all objects that have particular value add them to a new list. Can i do that or i need a Map? example code: import java.util.ArrayList; import java.util.List; …

How to fill a List of Lists?

You’ve created an empty list with initial capacity of 2 (i.e. the internal representation of the list won’t be resized until you’ve added 2 elements to it and are adding the third).

Then you try to get the first element from the empty list. Naturally this won’t work. You need to first add() as many inner lists (presumably 2) as you want, and then fill those inner lists.

You have not initialized the inner list. That’s the reason you are getting the error.

Following code will initialize each of the inner list.

int initialCapacity=2; List tmp = new ArrayList(initialCapacity); for(int i = 0; i < initialCapacity; i++) tmp.add(new ArrayList()); 

You haven't added anything to the list yet. Declaring a List of any type with an initial capacity of 2 doesn't automatically populate that. You have to do that first.

How to fill out an ArrayList with for each loop? (Java), You are creating the ArrayList with 10 as constructor parameters, which define it initial capacity (which is already 10 by default btw), but does not set any value. In other words, you try to iterate on an empty list, hence never enter it. You can't achieve this with a for-each, you could achieve this with a for.. final …

Filling a JList with data

• create a ListModel which wrapps your java.util.List (e.g. by extending AbstractListModel)
• configure JList to use this model
• create and configure a renderer to format/ display the Objects in your list as needed

You create a JList with a ListModel . When you edit your ListModel , it is reflected on JList as well.

I think it is having a little bit time with Google. I find the following results with Google.

• How to Use Lists
• Customize Your JList Display
• Basic Swing components II
• JLists, Data Models, and Cell Renderers

Initializing a List in Java, Initializing a List in Java. The Java.util.List is a child interface of Collection. It is an ordered collection of objects in which duplicate values can be stored. Since List preserves the insertion order, it allows positional access and insertion of elements. List Interface is implemented by ArrayList, LinkedList, …

How to save two values into a single variable fetched from a list in java

getAppropriateIssues() will return a List . With Count you probably mean the number of Issue in the List . Where does the Project come from?

In any way, if you want to store two variables into one, you can either

• use a Map and store the two values there
• or (probably the better way) is to use a Tuple / Pair class. You can either create one yourself or use the Apache Commons Pair.

If you want to implement a Pair class on your own it could look roughly like this:

public class Pair  < private A left; private B right; public Pair(A left, B right) < // assign >// getters + setters > 

You can use HashMap for storing the first value 'Project' as key and second value 'count' as value. Split the value returned by your query and put to hashmap.

HashMap resultMap = new HashMap(); 

Java - Filling a JList with data, 4 Answers. create a ListModel which wrapps your java.util.List (e.g. by extending AbstractListModel) create and configure a renderer to format/ display the Objects in your list as needed. +1, for being the first to link to the Swing tutorial which has a working example that does exactly what the OP wants to do.

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