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question:Currently, in my project, I have two files. A MainActivity.java(package com.example.AdTester; import androidx.annotation.NonNull; import androidx.appcompat.app.AppCompatActivity; import android.content.SharedPreferences; import android.os.Bundle; import android.util.Log; import android.view.View; import android.widget.Button; import android.widget.TextView; import android.widget.Toast; import com.google.android.gms.ads.AdError; import com.google.android.gms.ads.AdRequest; import com.google.android.gms.ads.AdView; import com.google.android.gms.ads.FullScreenContentCallback; import com.google.android.gms.ads.LoadAdError; import com.google.android.gms.ads.MobileAds; import com.google.android.gms.ads.OnUserEarnedRewardListener; import com.google.android.gms.ads.initialization.InitializationStatus; import com.google.android.gms.ads.initialization.OnInitializationCompleteListener; import com.google.android.gms.ads.interstitial.InterstitialAd; import com.google.android.gms.ads.interstitial.InterstitialAdLoadCallback; import com.google.android.gms.ads.rewarded.RewardItem; import com.google.android.gms.ads.rewarded.RewardedAd; import com.google.android.gms.ads.rewarded.RewardedAdLoadCallback; public class MainActivity extends AppCompatActivity { private InterstitialAd mInterstitialAd; public static final String REWARD_AD_UNIT_ID="ca-app-pub-3940256099942544/5224354917"; public int amount = 0; private RewardedAd mRewardedAd; private TextView mTextView; String text; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); loadAmount(); mTextView=findViewById(R.id.Coins); Button mButton = findViewById(R.id.RewardedbtnAds); text = getResources().getString(R.string.coins_message, amount); mTextView.setText(text); MobileAds.initialize(this, new OnInitializationCompleteListener() { @Override public void onInitializationComplete(@NonNull InitializationStatus initializationStatus) { } }); loadRewardedAds(); mButton.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View view) { showRewardAds(); loadRewardedAds(); } }); } private void showRewardAds() { if (mRewardedAd!=null) { mRewardedAd.show(MainActivity.this, new OnUserEarnedRewardListener() { @Override public void onUserEarnedReward(@NonNull RewardItem rewardItem) { amount += rewardItem.getAmount(); text = getResources().getString(R.string.coins_message, amount); mTextView.setText(text); saveAmount(); } }); } else { Toast.makeText(MainActivity.this,"Reward ads is not ready yet", Toast.LENGTH_SHORT).show(); } } private void loadRewardedAds() { AdRequest RewardedAdRequest1=new AdRequest.Builder().build(); RewardedAd.load(this, REWARD_AD_UNIT_ID, RewardedAdRequest1, new RewardedAdLoadCallback() { @Override public void onAdFailedToLoad(@NonNull LoadAdError loadAdError) { super.onAdFailedToLoad(loadAdError); mRewardedAd=null; } @Override public void onAdLoaded(@NonNull RewardedAd rewardedAd) { super.onAdLoaded(rewardedAd); mRewardedAd=rewardedAd; rewardedAd.setFullScreenContentCallback(new FullScreenContentCallback() { @Override public void onAdClicked() { super.onAdClicked(); } @Override public void onAdDismissedFullScreenContent() { super.onAdDismissedFullScreenContent(); } @Override public void onAdFailedToShowFullScreenContent(@NonNull AdError adError) { super.onAdFailedToShowFullScreenContent(adError); } @Override public void onAdImpression() { super.onAdImpression(); } @Override public void onAdShowedFullScreenContent() { super.onAdShowedFullScreenContent(); } }); } }); final boolean[] volt = {false}; AdView mAdView = findViewById(R.id.adView); AdRequest BannerAdRequest = new AdRequest.Builder().build(); Button bannerbutton = findViewById(R.id.BannerbtnAds); bannerbutton.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View view) { if (!volt[0]) { mAdView.loadAd(BannerAdRequest); mAdView.setVisibility(View.VISIBLE); volt[0] = true; } else { mAdView.setVisibility(View.GONE); volt[0] = false; } } }); loadInterstitialAd(); // Call this method to load the ad Button button = findViewById(R.id.IntbtnAds); button.setOnClickListener(view -> { if (mInterstitialAd != null) { mInterstitialAd.show(MainActivity.this); } else { Log.d("TAG", "The interstitial ad wasn’t ready yet."); loadInterstitialAd(); // Try to load again if it wasn’t ready when the button was clicked } }); Button resetButton = findViewById(R.id.resetButton); resetButton.setOnClickListener(view -> { amount = 0; saveAmount(); text = getResources().getString(R.string.coins_message, amount); mTextView.setText(text); }); } private void loadInterstitialAd() { AdRequest adRequest = new AdRequest.Builder().build(); InterstitialAd.load(this,"ca-app-pub-3940256099942544/1033173712", adRequest, new InterstitialAdLoadCallback() { @Override public void onAdLoaded(@NonNull InterstitialAd interstitialAd) { mInterstitialAd = interstitialAd; setInterstitialAdCallbacks(); } @Override public void onAdFailedToLoad(@NonNull LoadAdError loadAdError) { mInterstitialAd = null; } }); } private void setInterstitialAdCallbacks() { mInterstitialAd.setFullScreenContentCallback(new FullScreenContentCallback(){ @Override public void onAdDismissedFullScreenContent() { mInterstitialAd = null; loadInterstitialAd(); // Load a new ad when the current one is closed } @Override public void onAdFailedToShowFullScreenContent(@NonNull AdError adError) { mInterstitialAd = null; } // Implement other callbacks if needed }); } private void saveAmount() { SharedPreferences sharedPreferences = getSharedPreferences("UserPreferences", MODE_PRIVATE); SharedPreferences.Editor editor = sharedPreferences.edit(); editor.putInt("coinsAmount", amount); editor.apply(); } private void loadAmount() { SharedPreferences sharedPreferences = getSharedPreferences("UserPreferences", MODE_PRIVATE); amount = sharedPreferences.getInt("coinsAmount", 0); } private void resetCoins() { Button button = findViewById(R.id.IntbtnAds); button.setOnClickListener(view -> { if (mInterstitialAd != null) { mInterstitialAd.show(MainActivity.this); } else { Log.d("TAG", "The interstitial ad wasn’t ready yet."); loadInterstitialAd(); // Try to load again if it wasn’t ready when the button was clicked } }); } }) and a MyApplication.java(package com.example.AdTester; import android.app.Activity; import android.app.Application; import android.content.Context; import android.util.Log; import android.os.Bundle; import androidx.annotation.NonNull; import androidx.lifecycle.Lifecycle; import androidx.lifecycle.LifecycleObserver; import androidx.lifecycle.OnLifecycleEvent; import androidx.lifecycle.ProcessLifecycleOwner; import com.google.android.gms.ads.AdError; import com.google.android.gms.ads.AdRequest; import com.google.android.gms.ads.FullScreenContentCallback; import com.google.android.gms.ads.LoadAdError; import com.google.android.gms.ads.MobileAds; import com.google.android.gms.ads.appopen.AppOpenAd; import com.google.android.gms.ads.initialization.InitializationStatus; import com.google.android.gms.ads.initialization.OnInitializationCompleteListener; import java.util.Date; public class MyApplication extends Application implements Application.ActivityLifecycleCallbacks, LifecycleObserver { private AppOpenAdManager appOpenAdManager; private Activity currentActivity; public long loadTime = 0; @Override public void onCreate() { super.onCreate(); MobileAds.initialize( this, new OnInitializationCompleteListener() { @Override public void onInitializationComplete(InitializationStatus initializationStatus) {} }); ProcessLifecycleOwner.get().getLifecycle().addObserver(this); appOpenAdManager = new AppOpenAdManager(this); registerActivityLifecycleCallbacks(this); } @OnLifecycleEvent(Lifecycle.Event.ON_START) protected void onMoveToForeground() { // Show the ad (if available) when the app moves to foreground. appOpenAdManager.showAdIfAvailable(currentActivity); } public class AppOpenAdManager { private boolean isFirstLaunch = true; private Context applicationContext; // Store the Application context public AppOpenAdManager(Context context) { this.applicationContext = context.getApplicationContext(); // Store the application context to avoid NPE loadAd(applicationContext); } private static final String LOG_TAG = "AppOpenAdManager"; private static final String AD_UNIT_ID = "ca-app-pub-3940256099942544/9257395921"; private AppOpenAd appOpenAd = null; private boolean isLoadingAd = false; private boolean isShowingAd = false; /** Constructor. */ public AppOpenAdManager(MyApplication myApplication) {} /** Request an ad. */ private void loadAd(Context context) { // We will implement this below. if (isLoadingAd || isAdAvailable()) { return; } isLoadingAd = true; AdRequest request = new AdRequest.Builder().build(); AppOpenAd.load( context, AD_UNIT_ID, request, AppOpenAd.APP_OPEN_AD_ORIENTATION_PORTRAIT, new AppOpenAd.AppOpenAdLoadCallback() { @Override public void onAdLoaded(AppOpenAd ad) { // Called when an app open ad has loaded. Log.d(LOG_TAG, "Ad was loaded."); appOpenAd = ad; isLoadingAd = false; loadTime = (new Date()).getTime(); if(isFirstLaunch) { showAdIfAvailable(currentActivity); isFirstLaunch = false; } } @Override public void onAdFailedToLoad(LoadAdError loadAdError) { // Called when an app open ad has failed to load. Log.d(LOG_TAG, loadAdError.getMessage()); isLoadingAd = false; } }); } public void showAdIfAvailable( @NonNull final Activity activity){ // If the app open ad is already showing, do not show the ad again. if (isShowingAd) { Log.d(LOG_TAG, "The app open ad is already showing."); return; } // If the app open ad is not available yet, invoke the callback then load the ad. if (!isAdAvailable()) { Log.d(LOG_TAG, "The app open ad is not ready yet."); loadAd(MyApplication.this); return; } appOpenAd.setFullScreenContentCallback( new FullScreenContentCallback (){ @Override public void onAdDismissedFullScreenContent() { // Called when fullscreen content is dismissed. // Set the reference to null so isAdAvailable() returns false. Log.d(LOG_TAG, "Ad dismissed fullscreen content."); appOpenAd = null; isShowingAd = false; loadAd(activity); } @Override public void onAdFailedToShowFullScreenContent(AdError adError) { // Called when fullscreen content failed to show. // Set the reference to null so isAdAvailable() returns false. Log.d(LOG_TAG, adError.getMessage()); appOpenAd = null; isShowingAd = false; loadAd(activity); } @Override public void onAdShowedFullScreenContent() { // Called when fullscreen content is shown. Log.d(LOG_TAG, "Ad showed fullscreen content."); } }); isShowingAd = true; appOpenAd.show(activity); } /** Check if ad exists and can be shown. */ private boolean isAdAvailable() { return appOpenAd != null && wasLoadTimeLessThanNHoursAgo(4); } } private boolean wasLoadTimeLessThanNHoursAgo(long numHours) { long dateDifference = (new Date()).getTime() - this.loadTime; long numMilliSecondsPerHour = 3600000; return (dateDifference < (numMilliSecondsPerHour * numHours)); } @Override public void onActivityCreated(Activity activity, Bundle savedInstanceState) {} @Override public void onActivityStarted(Activity activity) { // Updating the currentActivity only when an ad is not showing. if (!appOpenAdManager.isShowingAd) { currentActivity = activity; } } @Override public void onActivityResumed(Activity activity) {} @Override public void onActivityStopped(Activity activity) {} @Override public void onActivityPaused(Activity activity) {} @Override public void onActivitySaveInstanceState(Activity activity, Bundle bundle) {} @Override public void onActivityDestroyed(Activity activity) {} }) I'm new to Android app developement. Can you please explain me, how does these two files link together? So when does each start to run? And can you please explain the basic concept of classes? I've only programmed in C before, so this is new to me. Please explain the classes (if those two different Java files are called classes) in a way that a that a small kid would understand, so please be clear.
answer:Welcome to the world of Android development! Coming from C, the concept of classes in Java (or any object-oriented programming language) is indeed somewhat different, but I'll try to make it as simple and clear as possible. In Java, a class is like a blueprint for creating objects. Think of a class as a recipe that defines how to make a specific type of object. It can include ingredients (variables) and steps (methods/functions) to create the final product, which is an instance of that class, also known as an object. Let's break down the two Java files (classes) you mentioned: # `MainActivity.java` This file defines a class named `MainActivity` which extends `AppCompatActivity`. This means `MainActivity` is a type of `AppCompatActivity` (like a special kind of recipe that inherits another recipe's steps) and it is tailored to be an Android activity. An "activity" in Android represents a single screen with a user interface. For example, when you open an app and see the home screen, that's one activity. `MainActivity` is where your user interface elements like buttons (`Button`) and text views (`TextView`) are set up and where you define what happens when users interact with those elements (like clicking a button). When your app starts and you see the first screen, `MainActivity` is running behind that screen, making it work. # `MyApplication.java` This file defines a class named `MyApplication` which extends `Application`. The `Application` class in Android represents your entire app. It gets created when your app starts, even before your activities (screens) like `MainActivity`. You can think of `MyApplication` as the overarching container for your app, managing its global state and lifecycle. The `MyApplication` class is especially useful when you need to maintain global application state, or setup things like advertising (like in your AdMob ads use case), analytics, and other services that need to be initialized once and retained throughout the entire app's life. # How They Link Together When you run your application, Android first starts your `MyApplication` class. It performs initial setup like initializing Mobile Ads, observing lifecycle events, etc., which you defined in `onCreate()` method. The `MyApplication` class is active as long as your app is running, regardless of what activity is currently being displayed. After `MyApplication` has started, Android then creates an instance of `MainActivity` for your first screen where you see your text views, buttons, and other UI elements. When you interact with those UI elements (`Views`), they respond using the code you wrote in event listeners (`onClick()`, etc.) inside `MainActivity`. In summary, `MyApplication` is the "container" that stays running during the whole life of your app, and `MainActivity` is the "room" that users start in when they enter your app. As users navigate through your app, they may enter and exit different "rooms" (`Activities`), but the "container" (`MyApplication`) remains constant. I hope this explanation helped! Let me know if you have any other questions about classes or Android development in general.
question:Thanks, that was very useful!
answer:You're welcome! I'm glad you found the explanation helpful. If you have any more questions about Android development, class structures, or anything else, feel free to ask. Happy coding!
question:Why is an error in android development is called Toast? I associate from toast to something totally different, especially a food
answer:In Android development, a "Toast" is not an error, but rather a short message that appears on the screen to provide feedback to the user. The name "Toast" might be considered a playful term in this context and does not relate directly to food. It is called a "Toast" because, like toast popping up from a toaster, the message pops up on the screen and then disappears after a short time without interrupting the user's interaction with the application. Toasts are typically used to inform users about an action that has taken place, such as: - Confirming that an item has been saved - Indicating that an input was invalid - Letting the user know that an action cannot be performed Here's an example of how to show a Toast in Android: ```java Toast.makeText(context, "This is a Toast message!", Toast.LENGTH_SHORT).show(); ``` The `makeText` method takes three parameters: 1. `context`: This is the context in which the Toast should be displayed. It's usually the current activity (`this` or `getApplicationContext()` for longer-lived Toasts). 2. `text`: The message you want to display to the user. 3. `duration`: How long the Toast should be visible. `Toast.LENGTH_SHORT` or `Toast.LENGTH_LONG` are the usual options. After calling `makeText`, `show()` is invoked to actually display the Toast on the screen. While Toasts are useful for simple feedback, they should not be used for critical messages, as they are only temporary and could be missed by the user. For more important feedback, developers may use other UI components, such as dialogs, snackbars, or directly display error messages on the screen.
question:Implement the following method that, given two stacks and an integer, moves entries between the two stacks so that the length of the first stack is equal to the given integer. Note that, as the ensures clause states, rev(leftStack) * rightStack must not be changed by the method. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 /** * Shifts entries between {@code leftStack} and {@code rightStack}, keeping * reverse of the former concatenated with the latter fixed, and resulting * in length of the former equal to {@code newLeftLength}. * * @param <T> * type of {@code Stack} entries * @param leftStack * the left {@code Stack} * @param rightStack * the right {@code Stack} * @param newLeftLength * desired new length of {@code leftStack} * @updates leftStack, rightStack * @requires <pre> * 0 <= newLeftLength and * newLeftLength <= |leftStack| + |rightStack| * </pre> * @ensures <pre> * rev(leftStack) * rightStack = rev(#leftStack) * #rightStack and * |leftStack| = newLeftLength} * </pre> */ private static <T> void setLengthOfLeftStack(Stack<T> leftStack, Stack<T> rightStack, int newLeftLength) {...} Note that setLengthOfLeftStack is a static, generic method: it is parameterized by the type T of the entries in the stacks. You can use the type T wherever you need to declare a variable that refers to an object of type T.
answer:Here's one possible implementation of the setLengthOfLeftStack method: private static <T> void setLengthOfLeftStack(Stack<T> leftStack, Stack<T> rightStack, int newLeftLength) { // Check if the desired new length is already equal to the current length if (newLeftLength == leftStack.size()) { return; // No need to make any changes } // Determine the number of elements to move from leftStack to rightStack int elementsToMove = leftStack.size() - newLeftLength; // Create a temporary stack to hold the elements to be moved Stack<T> tempStack = new Stack<T>(); // Move elements from leftStack to tempStack for (int i = 0; i < elementsToMove; i++) { tempStack.push(leftStack.pop()); } // Move elements from tempStack back to leftStack while (!tempStack.isEmpty()) { leftStack.push(tempStack.pop()); } }