How to sort keys in MAP while grouping

Question

I am trying to insert list of wrapper class records in a MAP taking group name as KEY and related Wrapper class records as value pair .

the wrapper classes were

public class SCQLWrapperClass
{
   public date stDate{get;set;}
   public date endDate{get;set;}

   public String stDate1{get;set;}
   public String endDate1{get;set;}

    public double months{get;set;}
    public double quantty{get;set;}
    public double ppMonth{get;set;}
    public double discount{get;set;}
    public double netPrice{get;set;}        
    public double billTotal{get;set;}
    public String itmDesc{get;set;}        

}

public class groupingWrapClass
{
    public String yearname{get;set;}
    public Double billingtotal{get;set;}
    public Double pricepermonth{get;set;}
    public Double netpricepermonth{get;set;}        
    public List<SCQLWrapperClass> grpClsLst{get;set;}

    public groupingWrapClass(String yearname,Double pricepermonth,Double netpricepermonth,List<SCQLWrapperClass> grpClsLst)
    {
       this.yearname = yearname;
       this.pricepermonth = pricepermonth;
       this.netpricepermonth = netpricepermonth;
       this.grpClsLst = grpClsLst; 
    }

}

The Map was

Map map_lineitems_Group=new Map();

i was inserting values into the map taking keys from a sorted list as per user case.

the list contains group names { XYZ, ABC}

What ever the way i insert

map_lineitems_Group.put('XYZ', keyvalues);
map_lineitems_Group.put('ABC', keyvalues);

or in reverse way

map_lineitems_Group.put('ABC', keyvalues);
map_lineitems_Group.put('XYZ', keyvalues);

while iterating in VF page and debug logs too it is giving ABC as 1st group and XYZ as 2nd group. But i want it to be same order as in list. This list is a dynamic list, so i cannot predict the order too..

I have tried to loop over the map with a duplicate map , but results the same ...

Is there any way to get the resulting map as desired...

Answer 1

Java has multiple map classes such as LinkedHashMap that preserve insertion order but Apex only has one map type which does not. So in Apex a work-around is to keep a separate list of the keys as lists preserve insertion order and get the keys to iterate through from the list:

private Map<string, groupingWrapClass> map_lineitems_Group
        = new Map<string, groupingWrapClass>();
private List<String> ordered_keys = new List<String>();

private void addToMap(String key, groupingWrapClass grouping) {
    map_lineitems_Group.put(key, grouping);
    ordered_keys.add(key);
}

private void xyz() {
    ...
    addToMap('XYZ', keyvalues);
    addToMap('ABC', keyvalues);
    ...
    // Run through the map keys in insertion order
    for (String key : ordered_keys) {
        groupingWrapClass grouping = map_lineitems_Group.get(key);
        ...
    }
}

PS

On exposing this to Visualforce, make both ordered_keys and map_lineitems_Group visible (add getters or make properties) and then e.g.:

<apex:pageBlockTable value="{!ordered_keys}" var="ordered_key">
<apex:column headerValue="Year Name" value="{!map_lineitems_Group[ordered_key].yearname}"/>
...
</apex:pageBlockTable>

as expressions in Visualforce use [] for map access.

You could also add an apex:variable to factor out the common map_lineitems_Group[ordered_key] expression.