@AuraEnabled
public static List<SelectOption> ObjectNames()
{
    system.debug('object is calling:::');
   List<SelectOption> ObjNames= new List<SelectOption>();
    ObjNames.add(new SelectOption('','--None--'));
    ObjNames.add(new selectoption('Pay_Element_Master__c','Pay Element'));
    ObjNames.add(new selectoption('CTC_Master__c','CTC Master'));
    ObjNames.add(new selectoption('Section_Master__c','Section Master'));
    return ObjNames;

public class SelectOption {
public SelectOption(String value, String label) {
    this.value = value;
    this.label = label;
    this.disabled = false;
    this.escapeItem = false;
}

public SelectOption(String value, String label, Boolean isDisabled) {
    this.value = value;
    this.label = label;
    this.disabled = isDisabled;
    this.escapeItem = false;
}

@AuraEnabled
public String label { get;set; }
@AuraEnabled
public String value { get;set; }
@AuraEnabled
public Boolean disabled { get;set; }
@AuraEnabled
public Boolean escapeItem { get;set; }

componentVal:function(component,event,helper){
    alert('iam component calling:::');
    var action=component.get("c.ObjectNames");
    action.setCallback(this,function(re){
        var state=re.getState();
        if(state==='SUCCESS'){
            alert(':::::::'+JSON.stringify(re.getReturnValue()));
        }
    });
    $A.enqueueAction(action);
}