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How to use a switch case in test cases without passing values to switch() method [duplicate]

I've looked at various Q&As on SO similar to this question but haven't found a solution.
What I have is an enum which represents different ways to view a TV Guide...
In the NDroid Application class
static enum guideView {
GUIDE_VIEW_SEVEN_DAY,
GUIDE_VIEW_NOW_SHOWING,
GUIDE_VIEW_ALL_TIMESLOTS
}
...when the user changes the view an event handler receives an int from 0-2 and I'd like to do something like this...
In an Android Activity onClick(DialogInterface dialog, int which) event handler
// 'which' is an int from 0-2
switch (which) {
case NDroid.guideView.GUIDE_VIEW_SEVEN_DAY:
...
break;
}
I'm used to C# enums and select/case statements which would allow something like the above and I know Java does things differently but I just can't make sense of what I need to do.
Am I going to have to resort to if statements? There will likely only ever be 3 choices so I could do it but I wondered how it could be done with switch-case in Java.
EDIT Sorry I didn't completely expand on the issue as I was looking at it as being a generic Java issue. I've added to the question to explain a bit further.
There isn't anything that's Android specific which is why I didn't tag it as Android but the enum is defined in the Application class and the code where I wan't the switch is in an Activity. The enum is static as I need to access it from multiple Activities.

The part you're missing is converting from the integer to the type-safe enum. Java will not do it automatically. There's a couple of ways you can go about this:
Use a list of static final ints rather than a type-safe enum and switch on the int value you receive (this is the pre-Java 5 approach)
Switch on either a specified id value (as described by heneryville) or the ordinal value of the enum values; i.e. guideView.GUIDE_VIEW_SEVEN_DAY.ordinal()
Determine the enum value represented by the int value and then switch on the enum value.
enum GuideView {
SEVEN_DAY,
NOW_SHOWING,
ALL_TIMESLOTS
}
// Working on the assumption that your int value is
// the ordinal value of the items in your enum
public void onClick(DialogInterface dialog, int which) {
// do your own bounds checking
GuideView whichView = GuideView.values()[which];
switch (whichView) {
case SEVEN_DAY:
...
break;
case NOW_SHOWING:
...
break;
}
}
You may find it more helpful / less error prone to write a custom valueOf implementation that takes your integer values as an argument to resolve the appropriate enum value and lets you centralize your bounds checking.

If whichView is an object of the GuideView Enum, following works well. Please note that there is no qualifier for the constant after case.
switch (whichView) {
case SEVEN_DAY:
...
break;
case NOW_SHOWING:
...
break;
}

The enums should not be qualified within the case label like what you have NDroid.guideView.GUIDE_VIEW_SEVEN_DAY, instead you should remove the qualification and use GUIDE_VIEW_SEVEN_DAY

I like a few usages of Java enum:
.name() allows you to fetch the enum name in String.
.ordinal() allow you to get the integer value, 0-based.
You can attach other value parameters with each enum.
and, of course, switch enabled.
enum with value parameters:
enum StateEnum {
UNDEFINED_POLL ( 1 * 1000L, 4 * 1000L),
SUPPORT_POLL ( 1 * 1000L, 5 * 1000L),
FAST_POLL ( 2 * 1000L, 4 * 60 * 1000L),
NO_POLL ( 1 * 1000L, 6 * 1000L);
...
}
switch example:
private void queuePoll(StateEnum se) {
// debug print se.name() if needed
switch (se) {
case UNDEFINED_POLL:
...
break;
case SUPPORT_POLL:
...
break;

This should work in the way that you describe. What error are you getting? If you could pastebin your code that would help.
http://download.oracle.com/javase/tutorial/java/javaOO/enum.html
EDIT: Are you sure you want to define a static enum? That doesn't sound right to me. An enum is much like any other object. If your code compiles and runs but gives incorrect results, this would probably be why.

Short associative function example:
public String getIcon(TipoNotificacao tipo)
{
switch (tipo){
case Comentou : return "fa fa-comments";
case ConviteEnviou : return "icon-envelope";
case ConviteAceitou : return "fa fa-bolt";
default: return "";
}
}
Like #Dhanushka said, omit the qualifier inside "switch" is the key.

enumerations accessing is very simple in switch case
private TYPE currentView;
//declaration of enum
public enum TYPE {
FIRST, SECOND, THIRD
};
//handling in switch case
switch (getCurrentView())
{
case FIRST:
break;
case SECOND:
break;
case THIRD:
break;
}
//getter and setter of the enum
public void setCurrentView(TYPE currentView) {
this.currentView = currentView;
}
public TYPE getCurrentView() {
return currentView;
}
//usage of setting the enum
setCurrentView(TYPE.FIRST);
avoid the accessing of TYPE.FIRST.ordinal() it is not recommended always

I am doing it like
public enum State
{
// Retrieving, // the MediaRetriever is retrieving music //
Stopped, // media player is stopped and not prepared to play
Preparing, // media player is preparing...
Playing, // playback active (media player ready!). (but the media player
// may actually be
// paused in this state if we don't have audio focus. But we
// stay in this state
// so that we know we have to resume playback once we get
// focus back)
Paused; // playback paused (media player ready!)
//public final static State[] vals = State.values();//copy the values(), calling values() clones the array
};
public State getState()
{
return mState;
}
And use in Switch Statement
switch (mService.getState())
{
case Stopped:
case Paused:
playPause.setBackgroundResource(R.drawable.selplay);
break;
case Preparing:
case Playing:
playPause.setBackgroundResource(R.drawable.selpause);
break;
}

using an array for a switch case statement in java

I'm making a game, and i want the controls to be editable. well, i've got that part down, but they are being read and changed in a .txt file. that is the way i wanted it to work for now. the values are stored as the key value (ie. KeyEvent.VK_W is equal to 83, so the value for the line is 83). I also have it reading the values and saving them to a String array variable in my core class. In my key event class, the one that handles the pushing of the keys, i have it refering to the array to check if a command key was pushed. i'm continuously getting this error: case expressions must be constant expressions when i try it. here is the WRONG code:
switch(key){
case Integer.parseInt(commands[1]):
...
break;
}
and i get that error. the value of commands[1] is 83. it is the value for "W". here is my declaration of the variable:
for (int i = 0; i < commands.length; i++) {
commands[i] = io.readSpecificLine(FILES.controlsFileFinalDir,
i + 1);
}
and if i have it print out every value, it does work. i've tried making the array final but that didnt work. i've run across the solution before, about 2 years ago, but i cant find it again. does anyone have any ideas on how to fix this? thanks in advance!

As the compiler says, the case expressions must be constant expressions. You can't use an array element as a case expression. You can simply use an if/else if/else clause instead.

You can't use non-constant expressions in case statements. An alternative approach is to build a map from values to the actions. So instead of this (which doesn't actually make any sense to me):
switch (key) {
case Integer.parseInt(commands[1]):
// action 1
break;
// other cases...
default:
// default action
}
You can do something like this:
static Map<Integer, Runnable> keyMap = new HashMap<Integer, Runnable>();
static {
keyMap.put(83, new Runnable() {
#Override
public void run() {
// actions for code 83
}
});
. . .
}
(If it makes more sense, this could also be done on a per-instance basis instead of as a static map.) Then later:
Runnable action = keyMap.get(Integer.parseInt(commands[1]));
if (action != null) {
action.run();
} else {
// default action
}
If you need to pass variables to your actions, you can define your own interface instead of using Runnable for the actions.

Weird compilation error when using switch on enumeration

I just noticed one curious case and wanted to see if someone will be able to explain it. Here is my case:
private enum Classifiers {
NEURAL_NETWORK, NEAREST_NEIGHBOURS, IDENTITY;
}
private ClassifierInterface getClassifierInstance(Classifiers classifier) {
switch (classifier) {
case NEURAL_NETWORK:
return new DoubleLayeredNeuralNetwork();
case NEAREST_NEIGHBOURS:
return new NearestNeighbours();
case IDENTITY:
return new IdentityClassifier();
}
return null; // If I comment out this line I get compilation error
}
See the comment. I would expect that Unreachable code error will be reported for this line. Instead I get Method must return value error if I comment out this line. However, there is no way the program flow will pass through there.
I even assumed it would be a guard case for the case of null value passed-in, but as expected this triggers NullPointerException for the switch condition.
I do not use switch very often, probably I am missing something here. Can somebody please try to help understand this behaviour?

That is correct behaviour as you do not have a default case statement. The problem is that you could add an value to the enum later and not re-compile the code which uses it. By forcing you to always handle when it is not one of the values, this is covered.
BTW: classifier could be null which is another option switch doesn't handle unfortunately.

That question is interesting...
We have something like this and the compiler is happy!
public enum Coin {
PENNY,
NICKEL,
DIME,
QUARTER;
}
private enum CoinColor { COPPER, NICKEL, SILVER }
private static CoinColor color(Coin c) {
switch(c) {
case PENNY:
return CoinColor.COPPER;
case NICKEL:
return CoinColor.NICKEL;
case DIME: case QUARTER:
return CoinColor.SILVER;
default:
throw new AssertionError("Unknown coin: " + c);
}
}
The Java Languaje Specification says:
A Java compiler is encouraged (but not required) to provide a warning
if a switch on an enum-valued expression lacks a default label and
lacks case labels for one or more of the enum type's constants. (Such
a statement will silently do nothing if the expression evaluates to
one of the missing constants.)

Using reserved words in an enum / switch statement, best workaround?

I am writing a flat file parser that reads token/value pairs using a Scanner. The files being read contain the token "class". The token is later used in a switch statement, and uses the (pre Java 7) valueOf(token) Java idiom to produce an enum value. (I am using Java6 for compatibility with GWT.) As a workaround, I am using uppercase values in the enum, and valueOf(token.toUpperCase()).
public enum ParseTags {
CODE, CLASS, INSTRUCTOR, HOURS;
}
// . . .
token = scanner.next();
value = scanner.next();
switch (ParseTags.valueOf(token.toUpperCase())) {
case CODE:
entry.setCode(value);
break;
case CLASS:
entry.setClass(value);
break;
Because this is being compiled into javascript, I want to avoid the extra "toUpperCase()" operation on each iteration; not sure what performance will be on target platform. Is there a more graceful way to represent reserved words in an enumeration? This would be handled well by Java7's switch on String, but again, I am confined to Java6sdk.

What you're doing right now is the preferred way to do it. I would be extraordinarily shocked if the toUpperCase were a bottleneck.
That said, I might consider something like
enum ParseTags {
CODE {
public void set(Entry entry, String value) {
entry.setCode(value);
}
},
...;
public abstract void set(Entry entry, String value);
}
so you can do
ParseTags.valueOf(token.toUpperCase()).set(entry, value);

How to convert my state machine to java?

Here is the normal way I would do things in C++:
class object
{
public:
enum
{
STATE_ACTIVE = 0,
STATE_INACTIVE,
OBJ_NUM_STATES,
}
int m_State;
virtual void UpdateState ()
{
switch(this->m_state)
{
case STATE_ACTIVE: /* do stuff*/ break;
case STATE_INACTIVE: /* do stuff*/ break;
}
}
}
class SpecialGameObject : public Object
{
public:
enum
{
STATE_SPECIAL_A = OBJ_NUM_STATES + 1,
STATE_SPECIAL_B,
SPECIAL_NUM_STATES,
}
virtual void UpdateState ()
{
Object::UpdateState();
switch(this->m_State)
{
case STATE_ACTIVE: /* do extra stuff */ break;
case STATE_SPECIAL_A: /* do special stuff*/ break;
case STATE_SPECIAL_B: /* do special stuff*/ break;
}
}
}
I am trying to figure out to get all of this functionality to work in java. Specifically I need working:
1) Ability for derived classes to have state values that automatically line up after the derived state values. That way I can add new state values to the base class without worrying about them overlapping the rage of state values used in any of the derived classes.
2) Ability to use the state values as cases in switch statements.
I looked into using static final ints to implement my state values. But those can't be used as case statements. Then I looked into extending enums, but that isn't allowed.
Does anyone have any suggestions for me?
Thank you

You need to implement the state pattern in Java. This might help you. Wikipedia also has a simple and easy to understand example in Java.

Is this enough to get you going?
final class GameObject {
enum State { ACTIVE, INACTIVE };
State state;
void updateState()
{
switch(state) {
case ACTIVE :
// update state
break;
case INACTIVE:
// update STATE
break;
default:
assert false : "never get here";
}
}
}
Note that in Java, enums are final so you can't extend an enum directly. (Reference this SO question.) If you really need to extend the notion of state into specialized subclasses, things are probably complicated enough that you should consider using polymorphism rather than switch statements (see also here) to get what you want. Alternatively, you could bundle the "super" state with specialized substates in a wrapper super- and sub-classes, perhaps with defined interfaces.
And, if you want to get seriously warped, you could do something like this. It's very cool that Java enums can implement interfaces, but I think this counts as a particularly ugly way of using that feature for your question...
final class GameObject {
ActiveStateful state;
interface ActiveStateful {
State activeState();
}
enum State implements ActiveStateful {
ACTIVE, INACTIVE;
public State activeState() {
return this;
}
};
enum SubState implements ActiveStateful {
SPECIAL_A(State.ACTIVE), SPECIAL_B(State.ACTIVE);
SubState(final State activeState) {
this.activeState = activeState;
}
final State activeState;
public State activeState() {
return activeState;
}
}
}

But those can't be used as case statements.
If I told you this was incorrect, that would solve your problems, yes? This is incorrect: you can switch on static final int constants.

I'd recommend using an enum and its ordinal values for switch statements. That's what enum was born for.

Please consider getting rid of switch altogether. It is a horrible abomination that should have ceased decades ago but didn’t. Read the excellent “Abandoning switch In Three (And A Bit) Steps” article for more information.