COLLECTIONS

Collections:

                 Difference between Arrays  and Collections.

     1.Array:

•  Array is a collection of homogenous (similar) elements.
• array can not grow and shrink dynamically.
• Array can be accessed faster and less memory

       2.Collections:

• its is a collection of homogeneous and heterogeneous elements.
• It can grow and shrink dynamically .
• Collections are slow compared to arrays. consume more memory.

                                1.List

                                2.Set

                                3.Map

1. LIST:

•      List is an interface
• A list is an ordered collection of elements that are distinguished by their indexes. 
• List elements can be of any datatype- primitive types, Collections,Sobjects, user-defined types and built-in apex types.
• Insertion order is preserved.
• Can grow dynamically at run time.
• Duplicate values are allowed.
• Null values are accepted.

Methods in List CLass:

1. add(object): add an element to the emd of the list.
2. add(Integer, Object): Insert an element into the at specified index position.
3. addAll(List): Adds all of there elements in the specified list to the list that calls the                                            method.Both lists must be of the sametype.
4. addAll(set); Add all of the elements in the specified set to the list that calls the method. the set and the list must be of the same type.
5. Clear(): removes all elements from a list, consequently setting the list's length to zero.
6. Clone():makes a duplicate copy of list.
7. deepClone)(Boolean, Boolean,Boolean); Makes a duplicate copy of a list of Sobject records,including the sobject records themselves.
8. equals(List); compares this list with the specified list and returns true if both lists are equal. otherwise returns false.
9. get(Integers): Returns the list elements stored at the specified index.
10. getSObjectType(): Returns the token of the Sobject type that takes a list of  sobjects.
11. hashcode():returns the hsdhcode corresponding to this list and its contents.
12. isEmpty(): Returns true if the list has zero elements.
13. iterator): Return an instace of an iterator for this list.
14. remove(Integer): Removes the list element stored at the specified index, returning the element that was removed.
15. set(Integer, Object): sets the specified value for the element at the index.
16. size(): Returns the number of elements in the list.
17. sort(): sorts the items in the list in ascending order. 

    

EX:

      List<string> str=new List<string>();

      string s1='sam';

      string       

      string s1='sam';

      string s2='Ram';

      string  s3='Ravi';

          str.adds(s1);

          str.add(s2);

           str.add(1,s3);

 LIst<string> finalist= new List<string>();

   finallist.addAll(str);

 string x=str.get(1); // Ravi

Ex: Write a programme to demonstrate the list

         public class ListExample{

         public List<string> result{set;get;}

          public ListExample()

              {

        result =new List<string>();

         result.add('sam');

           result.add('Ram');

           result.add('hari');

          result.add('1,'kumar'');

       }

 }

<apex:page controller="ListExample">
<apex;pageBlock>
<apex:pageBlockTable value=={result}" var="a">
<apex:column value="{!a}"/>
<apex:pageBlockTable>
<apex:pageBlockTable>
</apex:page>



List of Object Demo:-

  Public class ListExample{
Public List<account> result{set;get;}
Public ListExample()
{
Account a1=new Account(name='sam' Industry='Banking');
Account a2=new Account(name='ram; Industry='Eneregy';
result= new List<Account>();
result.add(a1);
result.add(a2);
}
}


<apex:page controller="ListExample">
<apex:pageBlock>
<apex:pageBlockTable value="{!result}" var="a">
<apex:column value="{!a.name}/>
<apex:pageBlockTbale>
<apex:pageBlock>
<apex:page>



Create  a List pf Apex class Objects:-

Student Apex:

global class Student
{
Public string name{get;set;}
Public Integer age(get;set;};
Public Student(String name, Integer age)
        {
      this.name=name;
       this,age=age;
               }
}



List Example Apex:

Public Class ListExample
{
Public List<Student>rsult{set;get;}
Public ListExample()
    {
result=new List<Student>();
Student s1=new Student('sam,20);
Student s2=new Student('Ram',40);
Student s3=new Student('apraveen',40);
result.add(s1);
result.add(s2);
result.add(s3);
        }
   }



ListExample VisualForce:

<apex:page controller="ListExample">
<apex:pageBlock>
<apex:pageBlockTable value="{!result}" var="a">
<apex:column value="{!a.name}/.>
<apex::column vallue="{!a.name}/>
<apex:column value="{!a.age}"/>
<apex:pageBlockTable>
<apex:pageBlock>
<apex:page>