How to create an Array ArrayList Stack and Queue in Java

Question

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  http   www theparticle com javadata2 html

User · Answer

I am guessing you re confused with the parameterization of the types      This works  because there is one class type definition in the parameterized  lt  gt  field ArrayList lt String gt  myArrayList   new ArrayList lt String gt           This doesn t work  as you cannot use primitive types here ArrayList lt char gt  myArrayList   new ArrayList lt char gt

User · Answer

Just a small correction to the first answer in this thread.

Even for Stack, you need to create new object with generics if you are using Stack from java util packages.

Right usage:
    Stack<Integer> s = new Stack<Integer>();
    Stack<String> s1 = new Stack<String>();

    s.push(7);
    s.push(50);

    s1.push("string");
    s1.push("stack");

if used otherwise, as mentioned in above post, which is:

    /*
    Stack myStack = new Stack();
    // add any type of elements (String, int, etc..)
    myStack.push("Hello");
    myStack.push(1);
    */

Although this code works fine, has unsafe or unchecked operations which results in error.

User · Answer

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     quot this quot    quot is quot    quot my quot    quot array quot    int   intArray    1 2 3 4    Create an ArrayList  ArrayList lt String gt  myList   new ArrayList lt String gt     myList add  quot Hello quot    myList add  quot World quot     ArrayList lt Integer gt  myNum   new ArrayList lt Integer gt     myNum add 1   myNum add 2    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    myStack push  quot Hello quot    myStack push 1    Create an Queue   using LinkedList  Queue lt String gt  myQueue   new LinkedList lt String gt     Queue lt Integer gt  myNumbers   new LinkedList lt Integer gt     myQueue add  quot Hello quot    myQueue add  quot World quot    myNumbers add 1   myNumbers add 2    Same thing as an ArrayList  this declaration means create an Queue of String and Integer objects   Update  In response to your comment from the other given answer   i am pretty confused now  why are using string  and what does  lt String gt  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 lt int gt  numbers   new ArrayList lt int gt                   should be an object  int is not an object  but Integer is  ArrayList lt Integer gt  numbers   new ArrayList lt Integer gt                   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        this name   name     this loc   location     this age   age      public void printDetails        System out println name    quot  is from  quot    location                                         quot  and is  quot    age    quot  old  quot           Here we have a Monster object  but now in our Main java 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 lt Monster gt  myMonsters   new ArrayList lt Monster gt      public Main         Monster yetti   new Monster  quot Yetti quot    quot The Mountains quot   77       Monster lochness   new Monster  quot Lochness Monster quot    quot Scotland quot   20        myMonsters add yetti       lt -- added Yetti to our list     myMonsters add lochness       lt --added Lochness to our list        for  Monster m   myMonsters            m printDetails                 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

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

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