Kevin Kevin - 1 year ago 113
Java Question

How to create an Array, ArrayList, Stack and Queue in Java?

I was reading a Java article, but found no differences in the declaration and was confused over. Can anyone list me out this?

Added the Article

Answer Source

Without more details as to what the question is exactly asking, I am going to answer the title of the question,

Create an Array:

String[] myArray = new String[2];
int[] intArray = new int[2];

// or can be declared as follows
String[] myArray = {"this", "is", "my", "array"};
int[] intArray = {1,2,3,4};

Create an ArrayList:

ArrayList<String> myList = new ArrayList<String>();

ArrayList<Integer> myNum = new ArrayList<Integer>();

This means, create an ArrayList of String and Integer objects. You cannot use int because thats a primitive data types, see the link for a list of primitive data types.

Create a Stack:

Stack myStack = new Stack();
// add any type of elements (String, int, etc..)

Create an Queue: (using LinkedList)

Queue<String> myQueue = new LinkedList<String>();
Queue<Integer> myNumbers = new LinkedList<Integer>();

Same thing as an ArrayList, this declaration means create an Queue of String and Integer objects.


In response to your comment from the other given answer,

i am pretty confused now, why are using string. and what does <String> means

We are using String only as a pure example, but you can add any other object, but the main point is that you use an object not a primitive type. Each primitive data type has their own primitive wrapper class, see link for list of primitive data type's wrapper class.

I have posted some links to explain the difference between the two, but here are a list of primitive types

  • byte
  • short
  • char
  • int
  • long
  • boolean
  • double
  • float

Which means, you are not allowed to make an ArrayList of integer's like so:

ArrayList<int> numbers = new ArrayList<int>(); 
           ^ should be an object, int is not an object, but Integer is!
ArrayList<Integer> numbers = new ArrayList<Integer>();
            ^ perfectly valid

Also, you can use your own objects, here is my Monster object I created,

public class Monster {
   String name = null;
   String location = null;
   int age = 0;

public Monster(String name, String loc, int age) { = name;
   this.loc = location;
   this.age = age;

public void printDetails() {
   System.out.println(name + " is from " + location +
                                     " and is " + age + " old.");

Here we have a Monster object, but now in our class we want to keep a record of all our Monster's that we create, so let's add them to an ArrayList

public class Main {
    ArrayList<Monster> myMonsters = new ArrayList<Monster>();

public Main() {
    Monster yetti = new Monster("Yetti", "The Mountains", 77);
    Monster lochness = new Monster("Lochness Monster", "Scotland", 20);

    myMonsters.add(yetti); // <-- added Yetti to our list
    myMonsters.add(lochness); // <--added Lochness to our list

    for (Monster m : myMonsters) {

public static void main(String[] args) {
    new Main();

(I helped my girlfriend's brother with a Java game, and he had to do something along those lines as well, but I hope the example was well demonstrated)

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