Incompatible key type Set<String> for Map<String,String> at line 23 column 6

Question

I am practicing salesforce and stuck with an error. Can someone help me out?

Error:

Incompatible key type Set for Map at line 23 column 6

Apex Class:

public class mapapex {
    public map<string,string> mst;
    public list<string> lst {get;set;}
    public set<string> str  {get;set;}
    public set<string> mod {get;set;}
    public list<string> s{get;set;};
    public mapapex(){
       mst= new map<string,string>();
       mst.put('India','rupee');
       mst.put('USA','Doller');
       mst.put('Japan','yen');  
    }
    public pagereference showkey(){
       str=mst.keyset();
       return null;
    }
    public pagereference showvalue(){
        lst=mst.values();
       return null;
    }
    public pagereference showmod(){
        s = mst.get(mod);
        return null;
    }        
}

VF Page:

<apex:page controller="mapapex" >
    <apex:form >
        <apex:pageBlock >
            <apex:commandButton value="showkeys" action="{!showkey}" rerender="one"/>
            <apex:dataList id="one" value="{!str}" var="a"> {!a} </apex:dataList>
            <apex:commandButton value="showvalue" action="{!showvalue}" rerender="two"/>
            <apex:dataList id="two" value="{!lst}" var="b"> {!b} </apex:dataList>
            <apex:outputlabel> Enter the value for key- India </apex:outputlable>
            <apex:inputText value="{!mod}"/>
            <apex:outputlabel> Value for key India is {!s}</apex:outputlable>
        </apex:pageBlock>
    </apex:form>
</apex:page>

Answer 1

You have defined mod in your controller to be a Set. And it looks like in your page you are trying to pass in a String.

Change:

public set<string> mod {get;set;}

To:

public String mod {get;set;}

Answer 2

You have to do few changes

1. Modify the declaration of

public set<string> mod {get;set;}
public list<string> s{get;set;}

to

public string mod {get;set;}
public string s{get;set;}

because those are actually string variables and not collection as your intention is to get the mod from user input as key and get the corresponding value from the map.

2. In your VF page, there is no code to invoke the showmod() method. So modify

<apex:outputlabel> Value for key India is {!s}</apex:outputlabel>

to

<apex:outputlabel id="three"> Value for key India is {!s}</apex:outputlabel>

and add

<apex:commandButton value="showmod" action="{!showmod}" rerender="three"/>

Hope this helps.

Answer 3

@Yusuf, There is also need to change in the following line:

Change:

s = mst.get(mod);

To:

s.add(mst.get(mod));