Flow EXample

public class PluginExample  implements Process.plugin{

    public Process.PluginResult invoke(Process.PluginRequest request){

        String name=(string)request.inputParameters.get('empName');

        name='My Name '+name;

        Map<String,Object> objMap=new Map<String,Object>();

        objMap.put('finalName',name);

        Process.PluginResult result=new Process.PluginResult(objMap);

        return result;

    }

    public Process.PluginDescribeResult describe(){

        Process.PluginDescribeResult result=new Process.PluginDescribeResult();

        result.inputParameters=new List<Process.PluginDescribeResult.inputParameter>{

            new Process.PluginDescribeResult.inputParameter('empName',Process.PluginDescribeResult.parameterType.String,true)

        };

        result.outputParameters=new List<Process.PluginDescribeResult.outputParameter>{

            new Process.PluginDescribeResult.outputParameter('finalName',Process.PluginDescribeResult.parameterType.String)

        };

        return result;

    }

}

VF page :

<apex:page >

    <flow:interview name="flow2" finishLocation="/apex/page1"> </flow:interview>

</apex:page>

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StandardSetController:

public class ListButton {

    public List<Account> accs {set;get;}

    public ListButton(ApexPages.StandardSetController controller){

        List<String> fields=new List<String>{'Name','Industry','phone'};

        controller.addFields(fields);

        accs=(List<Account>)controller.getSelected();

    }

    public void getData(){

        delete accs;

    }

}

<apex:page  standardController="Account" extensions="ListButton" action="{!getData}" recordSetVar="items">

    <apex:pageBlock title="Accounts">

                <apex:pageBlockTable value="{!accs}" var="a">

            <apex:column value="{!a.name}" />

            <apex:column value="{!a.industry}" />

        </apex:pageBlockTable>

    </apex:pageBlock>

</apex:page>