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Added second MVC example. This time the view is registered as observer to the model and gets update notifications that way.
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‎model-view-controller/src/main/java/com/iluwatar/model/view/controller/with/observer/App.java‎

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package com.iluwatar.model.view.controller.with.observer;
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/**
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*
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* In this second example the model-view relationship is different. This time we use the Observer pattern to notify
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* the {@link GiantView} each time the {@link GiantModel} is changed. This way the {@link GiantController} responsibilities
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* are narrowed and it only needs to modify the {@link GiantModel} according to the user input.
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*
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*/
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public class App {
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/**
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* Program entry point
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* @param args command line args
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*/
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public static void main( String[] args ) {
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// create model, view and controller
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GiantModel giant = new GiantModel(Health.HEALTHY, Fatigue.ALERT, Nourishment.SATURATED);
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GiantView view = new GiantView();
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GiantController controller = new GiantController(giant, view);
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// initial display
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controller.updateView();
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// controller receives some interactions that affect the giant
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// model modifications trigger the view rendering automatically
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controller.setHealth(Health.WOUNDED);
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controller.setNourishment(Nourishment.HUNGRY);
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controller.setFatigue(Fatigue.TIRED);
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}
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}

‎model-view-controller/src/main/java/com/iluwatar/model/view/controller/with/observer/Fatigue.java‎

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package com.iluwatar.model.view.controller.with.observer;
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/**
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*
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* Fatigue enumeration
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*
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*/
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public enum Fatigue {
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ALERT("alert"), TIRED("tired"), SLEEPING("sleeping");
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private String title;
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Fatigue(String title) {
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this.title = title;
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}
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@Override
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public String toString() {
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return title;
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}
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}

‎model-view-controller/src/main/java/com/iluwatar/model/view/controller/with/observer/GiantController.java‎

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package com.iluwatar.model.view.controller.with.observer;
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/**
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*
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* GiantController updates the giant model.
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*
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*/
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public class GiantController {
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private GiantModel giant;
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private GiantView view;
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public GiantController(GiantModel giant, GiantView view) {
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this.giant = giant;
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this.view = view;
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this.giant.registerObserver(this.view);
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}
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public Health getHealth() {
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return giant.getHealth();
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}
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public void setHealth(Health health) {
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this.giant.setHealth(health);
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}
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public Fatigue getFatigue() {
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return giant.getFatigue();
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}
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public void setFatigue(Fatigue fatigue) {
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this.giant.setFatigue(fatigue);
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}
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public Nourishment getNourishment() {
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return giant.getNourishment();
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}
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public void setNourishment(Nourishment nourishment) {
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this.giant.setNourishment(nourishment);
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}
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public void updateView() {
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this.view.displayGiant(giant);
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}
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}

‎model-view-controller/src/main/java/com/iluwatar/model/view/controller/with/observer/GiantModel.java‎

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package com.iluwatar.model.view.controller.with.observer;
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import java.util.ArrayList;
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import java.util.List;
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/**
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*
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* GiantModel contains the giant data.
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*
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*/
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public class GiantModel {
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private Health health;
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private Fatigue fatigue;
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private Nourishment nourishment;
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private List<GiantModelObserver> observers = new ArrayList<>();
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GiantModel(Health health, Fatigue fatigue, Nourishment nourishment) {
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this.health = health;
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this.fatigue = fatigue;
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this.nourishment = nourishment;
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}
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public Health getHealth() {
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return health;
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}
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public void setHealth(Health health) {
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this.health = health;
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notifyObservers();
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}
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public Fatigue getFatigue() {
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return fatigue;
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}
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public void setFatigue(Fatigue fatigue) {
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this.fatigue = fatigue;
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notifyObservers();
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}
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public Nourishment getNourishment() {
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return nourishment;
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}
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public void setNourishment(Nourishment nourishment) {
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this.nourishment = nourishment;
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notifyObservers();
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}
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@Override
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public String toString() {
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return String.format("The giant looks %s, %s and %s.", health, fatigue, nourishment);
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}
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public void registerObserver(GiantModelObserver observer) {
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observers.add(observer);
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}
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private void notifyObservers() {
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observers.stream().forEach((GiantModelObserver o) -> o.modelChanged(this));
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}
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}

‎model-view-controller/src/main/java/com/iluwatar/model/view/controller/with/observer/GiantModelObserver.java‎

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package com.iluwatar.model.view.controller.with.observer;
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/**
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*
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* GiantModelObserver is the interface for delivering update notifications.
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*
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*/
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public interface GiantModelObserver {
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void modelChanged(GiantModel model);
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}

‎model-view-controller/src/main/java/com/iluwatar/model/view/controller/with/observer/GiantView.java‎

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package com.iluwatar.model.view.controller.with.observer;
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/**
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*
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* GiantView displays the giant
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*
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*/
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public class GiantView implements GiantModelObserver {
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public void displayGiant(GiantModel giant) {
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System.out.println(giant);
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}
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@Override
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public void modelChanged(GiantModel model) {
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displayGiant(model);
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}
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}

‎model-view-controller/src/main/java/com/iluwatar/model/view/controller/with/observer/Health.java‎

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package com.iluwatar.model.view.controller.with.observer;
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/**
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*
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* Health enumeration
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*
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*/
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public enum Health {
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HEALTHY("healthy"), WOUNDED("wounded"), DEAD("dead");
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private String title;
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Health(String title) {
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this.title = title;
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}
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@Override
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public String toString() {
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return title;
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}
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}

‎model-view-controller/src/main/java/com/iluwatar/model/view/controller/with/observer/Nourishment.java‎

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package com.iluwatar.model.view.controller.with.observer;
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/**
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*
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* Nourishment enumeration
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*
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*/
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public enum Nourishment {
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SATURATED("saturated"), HUNGRY("hungry"), STARVING("starving");
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private String title;
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Nourishment(String title) {
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this.title = title;
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}
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@Override
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public String toString() {
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return title;
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}
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}

‎model-view-controller/src/test/java/com/iluwatar/model/view/controller/with/observer/AppTest.java‎

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package com.iluwatar.model.view.controller.with.observer;
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import org.junit.Test;
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import com.iluwatar.model.view.controller.with.observer.App;
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/**
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*
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* Application test
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*
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*/
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public class AppTest {
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@Test
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public void test() {
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String[] args = {};
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App.main(args);
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}
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}

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