<aura:component controller="DisplayCaseController" implements="force:appHostable">
    <aura:attribute name="record" type="Case[]"/>
    <ui:inputNumber label="Case ID" aura:id="CaseID"/><br/><br/>
    <ui:button label="Get Case" press="{ !c.getCaseFromId }"/><br/><br/>
    <aura:iteration var="c" items="{!v.record}">
         <p>{!c.Subject} : {!c.Description} : {!c.Status}</p>
    </aura:iteration>
</aura:component>

client-side controller:-

({
    getCaseFromId : function(component) {
        var caseID = component.find("CaseID").get("v.value");
        var action = component.get("c.getCaseFromId");
        action.setCallback(this, function(response){
            var state = response.getState();
            if (state === "SUCCESS") {
                component.set("v.record", response.getReturnValue());
            }
        });
        $A.enqueueAction(action);
    }
})

public class DisplayCaseController {
@AuraEnabled
public static Case getCaseFromId(Id caseID) {
if(caseID == null) {
return [SELECT ID, Subject, Description, STATUS from Case LIMIT 1];
}
List<Case> cases = [ SELECT Id, Subject, Description, Status from CASE where ID = :caseID ];
if(cases.size() == 0) {
return [SELECT ID, Subject, Description, STATUS from Case LIMIT 1];
} else {
return cases[0];
}
}
}

Challenge not yet complete... here's what's wrong: 
The client side controller does not refer to the 'getCaseFromId' method of the Apex controller class

Thnaks In Advance

Prashant