How to create a list of objects in Java

Question

What is the equivalent way to create a list of objects in Java like the C# way of doing it below (example from the web)? I have to write something in Java, but its new to me. I can't seem to find what I'm looking for when searching the web either.

List<Author> AuthorList = new List<Author>();

/*The following code snippet creates the Author objects and adds them to the List. */

AuthorList.Add(new Author("Mahesh Chand", 35, "A Prorammer's Guide to     ADO.NET", true, new DateTime(2003,7,10)));

AuthorList.Add(new Author("Neel Beniwal", 18, "Graphics Development with  C#", false, new DateTime(2010, 2, 22)));

AuthorList.Add(new Author("Praveen Kumar", 28, "Mastering WCF", true, new DateTime(2012, 01, 01)));

AuthorList.Add(new Author("Mahesh Chand", 35, "Graphics Programming with GDI+", true, new DateTime(2008, 01, 20)));

AuthorList.Add(new Author("Raj Kumar", 30, "Building Creative Systems", false, new DateTime(2011, 6, 3)));

You're close, but remember in java, method names start with lowercase instead of uppercase (and your variables should be too!). Try .add(.. instead of .Add( — lucasvw
– lucasvw, Commented Jun 30, 2016 at 15:32
In java List is an interface so you can't instatiate it. Try List<Author> AuthorList = new ArrayList<Author>(); — DCruz22
– DCruz22, Commented Jun 30, 2016 at 15:33

Dave Doknjas · Accepted Answer · 2016-06-30 16:36:56Z

2

In Java, you would just use a generic ArrayList.

import java.util.*;    
...    
ArrayList<Author> AuthorList = new ArrayList<Author>();
AuthorList.add(new Author("Mahesh Chand", 35, "A Prorammer's Guide to     ADO.NET", true, java.time.LocalDateTime.of(2003,7,10)));
...

Note that you could type the variable as 'List':

List<Author> AuthorList = new ArrayList<Author>();

But the original doesn't type to an interface, so the exact Java equivalent perhaps shouldn't either.

edited Jun 30, 2016 at 16:36

answered Jun 30, 2016 at 15:34

Dave Doknjas

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5 Comments

Andrew Over a year ago

That was probably a great idea including the import statement, I can see how that would have probably been missed too.

Dave Doknjas Over a year ago

@Bobby: I'm not sure what you mean by 'getting an option'.

Bobby Over a year ago

When I try your suggestion I'm getting an error that my constructor cannot be applied to given types. "required: no arguments". There must be an issue with my class in how its setup? I have private variables with public getters and setters.

Bobby Over a year ago

I was obviously getting myself confused with the basics in Java! It was my constructor that I needed to fix. Thanks for the help.

Bobby Over a year ago

@DaveDoknjas: Just as in what options are accepted or showing up in the intellisense after I type the ".add( " to my instantiated object.

Grayson · Accepted Answer · 2016-06-30 15:33:34Z

2

List is an interface. use ArrayList as follows:

List<Author> AuthorList = new ArrayList<Author>();

answered Jun 30, 2016 at 15:33

Grayson

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Comments

Andrew · Accepted Answer · 2016-06-30 15:33:53Z

1

List is an interface in java, so you cannot new a List. You can use an ArrayList, like this:
List<Author> AuthorList = new ArrayList<Author>();

answered Jun 30, 2016 at 15:33

Andrew

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Comments

Arnaud Denoyelle · Accepted Answer · 2016-06-30 15:44:53Z

In Java, List is an interface. Hence, you cannot instantiate it. You have to find the implementation that fits your need. Generally, ArrayList is a good starting point. LinkedList is quite useful too.

So you can create your list like this :

List<Author> list = new ArrayList<>();

(Note that the variable name begins with a lowercase letter : it is a Java convention).

Then, you can add some elements. In Java, every methods names shall start with a lowercase letter too. On a list, you can use the method add().

list.add(new Author(...));

Note : when you want to create a list of predefined values, you can use this shortcut method :

List<Author> authors = Arrays.asList(
    new Author(...),
    new Author(...)
);

But the resulting list is immutable. Trying to add an element will raise an exception at runtime.

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