classcastexception

Studying for my OCA Java SE 7 Programmer I exam, so newbie question. I have an example question I do not understand. The following code compiles, but gives a ClassCastException at runtime: interface Roamable { } class Phone { } public class Tablet extends Phone implements Roamable { public static void main(String... args) { Roamable var = (Roamable) new Phone(); } } When I change Roamable var = (Roamable) new Phone(); into Roamable var = (Roamable) new String(); I get a compilation error right away. Two questions: Why does the code above compile at all? Phone seems unrelated to Roamable to me?

I know this question has been asked before but they haven't been in the same situation I'm in. My problem I need to have my PostPhotosActivity class retainInstance. The way I'm doing that is turning it into a fragment. Unfortunately I'm always getting this error. 12-13 14:38:55.669: E/AndroidRuntime(30234): FATAL EXCEPTION: main 12-13 14:38:55.669: E/AndroidRuntime(30234): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{trade.ly.tradely/trade.ly.tradely.PostPhotosActivity}: java.lang.ClassCastException: trade.ly.tradely.PostPhotosActivity cannot be cast to android.app

Here is my stripped down class and enum. class A { @Enumerated (value = EnumType.STRING) AType type; } enum AType { X,Y } if I run query = FROM A a WHERE a.type = :type query.setParameter("type", AType.X); All is fine and dandy. However if I do the following: AType[] types = new AType[1]; types[0] = AType.X; query = FROM A a WHERE a.type IN (:types) query.setParameter("types", types); I get: Lcom.src.AType; cannot be cast to java.lang.Enum If I do: Enum[] types = new Enum[1]; types[0] = AType.X; query = FROM A a WHERE a.type IN (:types) query.setParameter("types", types); I get: Ljava.lang

I got an Actionbar and some Fragments. The Problem is my Homescreen. There is an overview Fragment on the left side and a detail Fragment on the right side. My TabListener is Dynamic so i want to set the weight of my Layout programatically. Whenever i try to get the Layoutparams of my LinearLayout i get a ClassCastException: 12-22 16:00:37.620: W/System.err(7235): java.lang.ClassCastException: android.widget.FrameLayout$LayoutParams cannot be cast to android.widget.LinearLayout$LayoutParams 12-22 16:00:37.625: W/System.err(7235): at com.coover.eu.lostandfound.ListSearchFragment.onViewCreated

ArrayList marks = new ArrayList(); Double sum = 0.0; sum = ((Double)marks.get(i)); Everytime I try to run my program, I get a ClassCastException that states: java.lang.Integer cannot be cast to java.lang.Double We can cast an int to a double but we can't do the same with the wrapper classes Integer and Double : int a = 1; Integer b = 1; // inboxing, requires Java 1.5+ double c = (double) a; // OK Double d = (Double) b; // No way. This shows the compile time error that corresponds to your runtime exception. Well the code you've shown doesn't actually include adding any Integers to the ArrayList