So I've read about the pass-by-value nature of Java and I've tried to change my variable after passing it to a function by having the function return the variable again. I didn't succeed in that.
My code
public class Logic {
private int position;
public class Logic(){
position = 1;
}
public void appendPosition(){
position = calculatePosition(position);
}
}
This is the barebones code. I call this method from an instance of Logic which is instantiated in another class:
public class MainLogic {
ILogic L;
public MainLogic(ILogic L){
this.L = L;
}
public void start(){
L.appendPosition();
}
}
Through repeated debugging I find to my dismay that the position variable does not change at all. The position variable passed to calculatePosition changes fine, as expected. What am I missing? I've tried making the variable public and static.
calculatePosition
private int calculatePosition(int position){
position += 6;
if(snakeLocations[position]>0) {
position -= 6;
}
else if(ladderLocations[position]>0) {
position += 6;
}
return position;
}
private final int[] snakeLocations = new int[] {0,0,0,0,0,0,0,0,0,9,0,0,0,13,0,0,0,0,0,19,0,0,0,0,0};
private final int[] ladderLocations = new int[] {0,0,0,0,0,0,0,0,0,0,0,11,0,0,0,15,0,0,0,0,20,0,0,0,0};
public class Logic {
private int position;
public Logic(){
position = 1;
}
//to get position.....................
public int getPosition(){
return this.position;
}
public void appendPosition(){
position = calculatePosition(position);
}
private int calculatePosition(int position){
position += 6;
if(snakeLocations[position]>0) {
position -= 6;
}
else if(ladderLocations[position]>0) {
position += 6;
}
return position;
}
private final int[] snakeLocations =
new int[] {0,0,0,0,0,0,0,0,0,9,0,0,0,13,0,0,0,0,0,19,0,0,0,0,0};
private final int[] ladderLocations =
new int[] {0,0,0,0,0,0,0,0,0,0,0,11,0,0,0,15,0,0,0,0,20,0,0,0,0};
}
//next class
public class MainLogic {
Logic L;
public MainLogic(Logic L){
this.L = L;
}
public void start(){
L.appendPosition();
}
public static void main(String[] args) {
Logic L = new Logic();
MainLogic ml = new MainLogic(L);
System.out.println(ml.L.getPosition());
ml.start();
System.out.println(ml.L.getPosition());
}
}
Let's read your code.
// There is a logic class.
public class Logic {
// So Logic has a position. it starts with zero.
private int position;
// Logic also has an inner class, also called Logic.
public class Logic(){
position = 1;
// When a new Logic().Logic() is created, the instance
// variable of the parent instance gets set to one. WHAT?!?
}
// ... lots of code
}
So, It's a bit like that Yo Dawg! meme - I heard you like Logic, so we've put A logic instance into your Logic instance so you can Logic while your Logic.
You probably want a constructor.
// So this is Logic.
public class Logic {
private int position;
// When an Logic instance is created, position starts with 1.
public Logic(){
this.position = 1;
}
Ok. So we're not talking about Yo Dawg Memes.
So Let's talk pass by value.
Pass-by-value means classes are like very egotistic children: You can't play with their toys, unless they tell you so.
This is a good thing® since this means only the owning instance is allowed to change their private state. Trust me, it prevents quite a bit of havoc.
One way to allow the outside world to actually change the state is by using query and mutator methods. Back in the day, we used to call them getter and setter, but that sounds too simple, so software architects will usually use the fancier term.
But... all of this doesn't really apply since calculatePosition() is defined at Logic. Oops.
Let's try this:
Renaming some instance variables
Be a bit verbose to help the debugger. baby steps.
(Also, dropping a few jokes to fish for upvotes).
public class Logic {
private int position = 1;
public void appendPosition(){
// When debugging strange stuff,
// keep each step simple.
// Is calculatePosition working as it should?
int newPosition = calculatePosition(this.position);
this.position = newPosition;
}
// Always use parameters as final. It's good karma.
// You don't NEED to declare them as final,
// but let's try to be EXTRA clear.
private int calculatePosition(final int targetPosition){
// Yes, make as much as you can immutable
// You'll save a ton of mental bandwidth.
final int localCopy = targetPosition +6;
if(snakeLocations[localCopy]>0) {
return (localCopy -6);
// Don't force the maintenance programmer to
// read all your stuff. Return often, return early.
// This isn't Cc++, where you need to
// actually free your reference/pointers,
// so there's no point enforcing a single return.
}
if(ladderLocations[localCopy]>0) {
return (localCopy+6);
}
return localCopy;
}
}
So... Did this worked as it should?
I found the answer. This is often my mistake in posting here. I try to strip down my code as much as possible to ease the work for you guys, but sometimes the problem lies outside of the scope of what I provide due to a lack of understanding, or oversight, on my part.
I was actually calling MainLogic from two levels above:
public mainFrame() {
initComponents();
logic = Factory.getMainLogic();
}
where
public static class Factory {
public MainLogic getMainLogic(){
PlayerLogic pL = new PlayerLogic();
ImageLogic iL = new ImageLogic();
DieLogic dL = new DieLogic();
MainLogic mainLogic = new MainLogic(pL,iL,dL);
return mainLogic;
}
}
I forgot I had accidentally put Factory as static. My sincerest apologies for wasting your time.
Related
I'm new to Java programming, sorry if this is a dumb question.
I find it hard to word this question properly, but I have an assignment to create a aircraft class that can make aircraft land, takeoff etc. And need to test it using Testclass. When the new object are entered it automatically assigns a unique ID to the aircraft in the constructor.
I can do this using a instance method fine as it has a return value which is returned to to Testclass. The question wants me to do this in the constructor itself, however, the constructor never returns anything. So the variable never gets sent to the Testclass. I clearly am not understanding OOP properly. Even when I try to just use a getter method to get the ID created in the constructor it gives me the initialized variable before the the constructor has worked on this. This is the code I have so far and its completely wrong I know but if someone could point me in the right direction or tell me how to word this question better it would be a massive help.
// I need to enter 3 aircraft into the system in the testclass
public class Aircraft {
private int aircraftID;
private static int lastID;
private String airportcode;
private int ID = 100;
private int count;
public Aircraft(int a, int b, int c){
// Constructor
// Assign ID
this.ID = a;
lastID = ID;
ID++;
this.ID =b;
lastID = ID;
ID++;
}
}
OK, you want to create an Aircraft that has an automatically-assigned unique identifier, and can take off and land. That implies you need a field for tracking the identifier, a field for tracking whether it's in the air (or not), and methods for the take off and land operations. You also need a static field for generating the unique identifiers. (Note that this implementation isn't thread safe.)
private class Aircraft {
private static int staticId = 0;
private int uniqueId = 0;
private boolean onGround = true; // Aircraft start on the ground in this implementation
public Aircraft(){
this.uniqueId = staticId; // putting this line first makes uniqueId zero-indexed in effect
staticId++;
}
public void land(){
onGround = true;
}
public void takeoff(){
onGround = false;
}
public boolean isFlying(){
return !onGround; // If it's not on the ground, it's flying
}
public int getUniqueId(){
return uniqueId;
}
}
Unit tests checks all of the methods and expected functionality of the class in question:
import org.junit.Test;
import static org.junit.Assert.*;
import Aircraft;
class Testclass {
private final Aircraft aircraft = new Aircraft();
#Test
public void hasId(){
aircraft.getUniqueId() >= 0;
}
#Test
public void canLand(){
assertTrue(aircraft.land());
}
#Test
public void canTakeOff(){
assertTrue(aircraft.takeOff());
}
#Test
public void checkFlightOperationsAreTrackedCorrectly(){
aircraft.land();
assertFalse(aircraft.isFlying());
aircraft.takeOff();
assertTrue(aircraft.isFlying());
}
}
As pointed out a constructor does not return anything (the simplified version is that with new it returns an object instance). I am kinda guessing at what you are trying to acomplish, but I'll have a go anyways. It seems to me that you are trying to cram the construction of 3 objects into one constructor - which is why your constructor has 3 parameters. Also you are playing havoc with the IDs.
I have removed all the variables that I didnt quite understand, leaving only ID that increments with each instantiated Aircraft. The #Override is mainly just for show.
public class Aircraft {
private int aircraftID;
private static int lastID = 0;
#Override
public String toString(){
return "Aircraft_" + this.aircraftID;
}
public Aircraft() {
lastID++;
this.aircraftID = lastID;
}
}
I took the liberty and wrote the TestClass just to see if we have the same thing in mind. Again the printAircraft() method is for show.
public class TestClass {
private List<Aircraft> aircrafts;
public TestClass(){
aircrafts = new ArrayList<>();
}
public void addAircraft(Aircraft a){
aircrafts.add(a);
}
public void printAircraft(){
Iterator<Aircraft> it = aircrafts.iterator();
while(it.hasNext()){
System.out.println(it.next().toString());
}
}
}
and to test it, we create and instance of TestClass add 3 Aircraft instances and print out the contents
public static void main(String[] args) {
TestClass tc = new TestClass();
tc.addAircraft(new Aircraft());
tc.addAircraft(new Aircraft());
tc.addAircraft(new Aircraft());
tc.printAircraft();
}
This would be the case if you are to write the TestClass. If that is given, it would help to know what it looks like - maybe that would help us understand better.
I'm quite new to programming and java in general. I am currently a student and I'm trying to do a project outside of the classroom to make myself more proficient in java.
Currently, I am working on a text-based RPG where I am trying to create the main character, assign the basic skill points to the character and use that info throughout the game.
So far, I've made a jframe class where the user has 6 different skills with a base value of 1. The user can add or deduct a value from the certain skill with plus and minus buttons.
And here is where I got stuck. I don't know how to save these values to an object which can be used by other classes.
I would really appreciate any help I could get.
Thank you.
public class CharacterStatsGUI extends javax.swing.JFrame {
static int skill1 = 1;
static int skill2 = 1;
static int skill3 = 1;
static int skill4 = 1;
static int skill5 = 1;
static int skill6 = 1;
static int skillPoints = 10;
private void txthealthActionPerformed(java.awt.event.ActionEvent evt) {
// TODO add your handling code here:
txthealth.setText(String.valueOf(skill1));
}
private void btnhpActionPerformed(java.awt.event.ActionEvent evt) {
// TODO add your handling code here:
if(skillPoints >= 1){
skill1++;
skillPoints--;
txthealth.setText(String.valueOf(skill1));
txtpoints.setText(String.valueOf(skillPoints));
}
else{
JOptionPane.showMessageDialog(null, "You dont have enough skills points");
}
}
private void btnhmActionPerformed(java.awt.event.ActionEvent evt) {
// TODO add your handling code here:
if(skillPoints >= 0 && skill1 > 1){
skill1--;
skillPoints++;
txthealth.setText(String.valueOf(skill1));
txtpoints.setText(String.valueOf(skillPoints));
}
else{
JOptionPane.showMessageDialog(null, "Minimum skill value is 1.");
}
}
There are more than one solution for this problem.
Not all of them are efficient, not all are beautiful, but if it is "to make yourself more proficient in java, it is good to know the various ways! Here's some options:
You can change static int skill1 = 1; with public static int skill1 = 1;, and thake that data by calling myCharacterStatsGUI.skill1.
Better than the firs option, you can make this int private and create some public methods like public int getSkill1, or public int getSkill(int numSkill) that returns the int value of the correct skill.
A lot of programmer suggest that the GUI shouldn't related with the data and so, you can create a class MainCharacter, that contains all the character values, skills included. This class must implements the option 2 methods.
Better than the third point, you can separate the MainCharacter class from its values, and store all the skills in a inner class Skills. When you want to pick up these values by calling a specific method. In the following code I want to show you this option:
public Class MainChar{
private Skills skills;
public MainChar(){
this.skills=new Skills();
}
/* Call it from your CharacterStatsGUI class,
in the method txthealthActionPerformed */
public void augmentSkill(){
skills.augment()
}
public int getHealt(){
return skills.getHealt();
}
private class Skills{
/*This example use only a skill, but
you can extend it with others values*/
private int health;
public Skills(){
health=1;
}
public void augment(){
health++;
}
public int getHealt(){
return health;
}
}
}
I am trying to convert this data type to call out the method later on in another class to switch around layouts being made in other methods such as recipe1Layout(); by the index number of a class that has a field of a Class<?> Array.
Here is the getItem() method
public int getItem(){
int index = 0;
for(int i = 0; i < 100; i++) {
try{
index = recipe.getClass().getField("Classes").get(i);
} catch(Exception e){
}
}
return index;
}
Here is the Recipe Class
public class Recipes {
public Class<?>[] Classes = {
ChileConLecheActivity.class,
ArrozActivity.class,
EnchiladasActivity.class,
SopaActivity.class
};
}
The type of Class needs to be here because I have other uses for the recipe class.
For example, making a new instance of all classes to later on be called out to make adjustments to all the classes with one method.
The only thing I can think of is converting the type Class to an int so I can call out the method returning the index number I can do something like recipe.
index = Integer.parseInt(Classes[I].getName().toString());
But this is where I am asking for help I have no idea how to get rid of the error in the logcat.
The error shows up as
IndexOutOfArrayException
First off, stop using reflection. Use a public static array.
public class Recipes {
public static final Class<?>[] CLASSES = {
ChileConLecheActivity.class,
ArrozActivity.class,
EnchiladasActivity.class,
SopaActivity.class
};
}
Then, assuming your recipe instance has a field of what Class<Activity> it is assigned to, then, you would want something like this
public int getItem(){
int index = -1;
for(int i = 0 ; i < Recipe.CLASSES.length; i++) {
if (recipe.getActivityClass().equals(Recipe.CLASSES[i]) {
index = i;
break;
}
}
return index;
}
However, under certain situations, coupling one Activity class to any single Recipe instance, probably isn't a good idea.
I am trying to convert this data type to call out the method later on in another class to switch around layouts being made in other methods
if I understand what you are trying to do, you want a some mapping structure to some classes which have some pre-defined layouts.
Generally, this can be done with enums and OOP patterns
Have some base classes like this
public interface Layoutable {
int getLayout();
}
public enum Recipe {
ChileConLeche(R.layout.chile_con_leche),
Arroz(R.layout.arroz),
Enchiladas(R.layout.enchiladas),
Sopa(R.layout.sopa)
int layout;
Recipe(int layout) { this.layout = layout };
}
Ideally, you would want to use Fragments, but here is an example of an Activity structure
public abstract class RecipeActvity extends AppCompatActivity implements Layoutable {
protected Recipe recipe;
protected int getLayout() { return recipe.layout; }
}
public class ChileConLecheActivity extends RecipeActvity {
public ChileConLecheActivity() {
this.recipe = Recipe.ChileConLeche;
}
#Override
public void onCreate(...) {
setContentView(getLayout());
}
}
You can also combine this with a Map<Recipe, Class<RecipeActivity>>, from which you would use map.get(Recipe.ChileConCarne) to get the respective class element, for which you can startActivity() with
I'm having problems with two void methods. In encouragedVenturesScoring I've followed this answer mocking an arraylist that will be looped in a for loop and haven't mocked the list, but passed a real list and added mocked objects.
Mockito gives me an InvalidUseOfMatchersException on this line
verify(effectList.get(Mockito.anyInt())).execute(playerHandler);
There are lots of questions on SO on this exception , and I think it's because of anyInt(). Anyway I changed it to
verify(effectList.get(0)).execute(playerHandler);
And now it's saying Wanted but not invoked effect.execute(playerHandler)
Actually there were zero interactions with this mock
Is it because I put doNothing ?
doNothing().when(effect).execute(playerHandler);
In my second method militaryStrengthScoring() method is there a way to skip the first chunk of code and just test the if..else condition? What would be the best approach to test this method?
Thank you for your time.
This is the class to be tested
public class EndGameScoringBaseController implements EndGameScoringHandler {
private static final int[] TERRITORIES_REWARD = {0,0,1,4,10,20};
private static final int[] CHARACTERS_REWARD = {1,3,6,10,15,21};
private static final int RESOURCES_RATE = 5;
private static final int FIRST_MILITARY_REWARD = 5;
private static final int SECOND_MILITARY_REWARD = 2;
private PlayerHandler player;
public EndGameScoringBaseController(PlayerHandler player) {
super();
this.player = player;
}
#Override
public void encouragedVenturesScoring() {
for (DevelopmentCard card : player.getPlayer().getPersonalBoard().getVentures()) {
for (Effect e : card.getPermanentEffects())
e.execute(player);
}
}
#Override
public void militaryStrengthScoring(GameController game) {
Set<Integer> points = new HashSet<>();
int myPoints = this.player.getPointsHandler().getMilitaryPoints();
for (PlayerHandler p: game.getPlayers()) {
points.add(p.getPointsHandler().getMilitaryPoints());
}
int[] rank = new int[points.size()];
int j = 0;
for (Integer i : points) {
rank[j] = i;
j++;
}
Arrays.sort(rank);
if (rank[rank.length-1] == myPoints) {
player.getPointsHandler().winMilitaryPoints(FIRST_MILITARY_REWARD);
}
else if (rank[rank.length-2] == myPoints) {
player.getPointsHandler().winVictoryPoints(SECOND_MILITARY_REWARD);
}
}
Tested method for encouragedVenturesScoring
#Test
public void encouragedVenturesScoringTest() {
//given
List<DevelopmentCard> ventureList;
ventureList = Arrays.asList(developmentCard, developmentCard);
when(playerHandler.getPlayer().getPersonalBoard().getVentures()).thenReturn(ventureList);
List<Effect> effectList;
effectList = Arrays.asList(effect, effect);
when(developmentCard.getPermanentEffects()).thenReturn(effectList);
doNothing().when(effect).execute(playerHandler);
//when
endgameController.encouragedVenturesScoring();
//then
verify(effectList.get(Mockito.anyInt())).execute(playerHandler);
}
Incomplete tested method for militaryStrengthScoring
#Test
public void militaryStrengthScoringTest() {
//given
when(playerHandler.getPointsHandler().getMilitaryPoints()).thenReturn(4);
doNothing().when(playerHandler.getPointsHandler()).winMilitaryPoints(FIRST_MILITARY_REWARD);
//when
endgameController.militaryStrengthScoring(gameController);
//then
/../
}
You're right that this is the problem:
verify(effectList.get(Mockito.anyInt())).execute(playerHandler);
Mockito only allows for calls like any() and anyInt() to stand in for parameters to the mock themselves, due to the internal implementation of matchers.
/* OK */ when(yourMock.yourMethod(anyInt())).thenReturn(42);
/* BAD */ when(yourList.get(anyInt()).yourMethod(0)).thenReturn(42);
/* OK */ verify(yourMock).yourMethod(anyInt());
/* BAD */ verify(yourList.get(anyInt())).yourMethod(0);
The failure with get(0) is likely an actual failure, and may be related to the fact that your encouragedVenturesScoringTest is actually not calling encouragedVenturesScoring, it's calling influencedCharactersScoring. If this continues to give you trouble after fixing that error, in ways related to Mockito, please edit your question.
You can only verify mock objects created by Mockito.
But effectList is a "real" list. Therefore Mockito knows nothing about that object. Thus any attempt to verify that list must fail.
If you want to verify that object - then you have to mock it!
Of course, this means that you have specify all calls that will go to the mocked list.
I'm still a relative newbie when it comes to Java, coming mainly from a C# background.
I was discussing the lack of 'out' parameters in Java methods with a colleague and how to work around this. He suggested creating a structure/class to hold the various parameters and passing it back.
Sometimes this feels 'wrong' to me - especially if I have a special method that I want to use to return a subset of parameters from a larger class.
So I wondered about using anonymous inline classes instead to achieve this. Code sample below.
Is this a sensible approach? Just wondering what the perceived wisdom is on this.
public class MyClass {
Patient myPatient = null;
// An interface to enable us to return these variables in a single call
public interface VitalStatsResponse { public void returnStats(int bloodPressure, int heartRate); }
public class Patient {
int bloodPressure = 100;
int heartRate = 280;
// Lots of other variables here
public void calculateVitalStats(VitalStatsResponse response)
{
response.returnStats((bloodPressure * 2), (heartRate / 10) ;
}
}
public void doWork()
{
// We want the patient's blood pressure and heart rate returned by a single method call, so use an anonymous inline class
myPatient.calculateVitalStats(new VitalStatsResponse() {
#Override
public void returnStats(int bloodPressure, int heartRate) {
// Handle returned variables here
}
});
}
}
I would go for the simple solution of creating a VitalStats object. If you need the VitalStatus of a patient, then VitalStats is a concept in your application that can be represented as an Object.
public class VitalStatus {
final int bloodPressure;
final int heartRate;
public VitalStats(int bloodPressure, int heartRate) {
this.bloodPressure = bloodPressure;
this.heartRate = heartRate;
}
}
public class Patient {
int bloodPressure = 100;
int heartRate = 280;
// Other variables
public VitalStatus getVitalStatus() {
return new VitalStats(bloodPressured * 2, heartRate / 2);
}
}
Out params is a procedural solution for return times. Java primarily fits the Object Oriented paradigm of programming and as such don't be afraid to make objects. This fits with the S in SOLID if your class is doing a lot of complex things see if you can break it down into smaller more manageable pieces.
I would also use "class to hold the parameters" over "inline anonymous inner class"
public class MyClass implements VitalStatsResponse{
Patient myPatient = null;
private ArrayList<VitalStatsResponse> response;
void MyClass(ArrayList<VitalStatsResponse> response) {
this.response = response;
}
public class Patient {
int bloodPressure = 100;
int heartRate = 280;
// Lots of other variables here
public void calculateVitalStats()
{
for(int i = 0; i < response.length; i++) {
// call returnStats method of every registered callback
response.get(i).returnStats((bloodPressure * 2), (heartRate / 10) ;
}
}
}
// any client can register/unregister callback via these methods
void registerResponse(VitalStatsResponse response) {
this.response.add(response);
}
void unRegisterResponse(VitalStatsResponse response) {
this.response.remove(response);
}
public void doWork()
{
// We want the patient's blood pressure and heart rate returned by a single method call, so use an anonymous inline class
myPatient.calculateVitalStats();
}
public void returnStats(int bloodPressure, int heartRate) {
// implement the body according to this class requirement
}
}