Thread: ArrayList<> String searches and loops

What happens when the code is compiled?
If there are no compiler errors, what happens when the code is execute?

My method finds them, but doesn't return them.

How do you know that?
Where is the code that tests this method?

I know it finds them

Ok, then there is no problem with the method. You have tested it and it works for you.

Why do you think there is a problem?
Can you compile and execute the code and print out the results and post those results so I can see what you see when the code is executed.

Also post the code that calls the methods and prints out the results for the tests you are doing.
Normally that would be in the main() method.

I think there's a problem because when I execute that method the dialog box in BlueJ doesn't show the names of the apps by the given author. Also, I haven't been able to return an empty list.

import java.util.ArrayList;
import java.util.Scanner;
import java.util.Collections;
 
/**
 * An app store containing apps
 */
 
public class AppStore
{
    private String appStoreName;
    private ArrayList<App> appList;
 
    /**
     * Create an app store with the given name
     * @param name the name of this app store
     */
    public AppStore(String name)
    {
        appStoreName = name;
        appList = new ArrayList<App>();
    }
 
    /**
     * Populate the store with a few apps.
     * Use this method to make testing easier. After creating an AppStore,
     * call this method to populate the apps, and then test your methods.
     */
    public void populateApps()
    {
        addApp("Pandora Music", "Pandora", 0);
        addApp(new App("Minecraft", "Mojang", 6.99, 3));
        addApp(new App("Coinbase", "Coinbase Global Inc.", 0, 0)); 
        addApp(new App("Telegram Messenger", "Telegram FZ LLC", .99, 0));
        addApp(new App("IPTV Extreme", "Paolo Turatti", 1.99, 0));
 
    }
 
    /**
     * Add the given app to the app store
     * @param anApp an app to add
     */
    public void addApp(App anApp)
    {
        appList.add(anApp);
    }
 
    /**
     * Create an app with the given name, author, and price and add it to the store.
     * The app starts out unrated.
     * @param name name of the app
     * @param author the app author
     * @param price the price of the app
     */
    public void addApp(String name, String author, double price)
    {
        appList.add(new App(name, author, price));
    }
 
    /**
     * @return the number of apps in the store
     */
    public int getNumberOfApps()
    {
        return appList.size();
    }
 
    /**
     * Removes all the apps from the store
     */
    public void clearAppStore()
    {
        appList.clear();
    }
 
    /**
     * Print all the apps in the store
     */
    public void printAppList()
    {
        System.out.println("============= " + appStoreName + " =============");
        if (appList.size() == 0) {
            System.out.println("No apps in the store");
        }
        else {
            for (App currentApp : appList) {
                currentApp.printAppInfo();
            }
        }
        System.out.println("===========================================");
    }
 
    /**
     * Find an app by name
     * @param the name of the app being looked for
     * @return the name of the app if found
     */
    public App findApp(String name)
    {
        for(App app : appList) {
            if(app.getName().equals(name)) {
                return app;
            }
        }
        return null;
    }
 
    /**
     * @remove an app from the App store
     * @param is name of app to remove
     */
    public App removeApp(String name)
    {
        App removeApp = null;
        for(App app : appList) {
            if(app.getName().equals(name)) {
                appList.remove(app);
                removeApp = app;
                break;
            }
        }
        return removeApp;
    }    
 
    /**
     * Find apps by same author
     * @param is name of given author
     * @return list of apps by given author
     * If no apps by author, return empty list, not null
     * Do not print anything
     */
    public ArrayList<App> getAppsByAuthor(String name)
    {
        ArrayList<App> appsByAuthor = new ArrayList<App>();
        for(App app : appList) {
            if (app.getAuthor() != (name)) {
 
            }
 
            if (app.getAuthor().equals(name)) {
                appsByAuthor.add(app);    
            }
        }
        return appsByAuthor;
 
    }
}
 
App Class
 
/**
 * An app for a mobile device
 * 
 
 */
public class App
{
    private String name;
    private String author;
    private double price;
    private int rating; // valid ratings are 1-4 or 0 meaning not rated
 
    /**
     * Create an app with the given name, author, price, and rating
     * @param appName the app name
     * @param appAuthor the app author
     * @param appPrice the price of the app (0 if the app is free)
     * @param appRating the app's rating
     */
    public App(String appName, String appAuthor, double appPrice, int appRating)
    {
        name = appName;
        author = appAuthor;
        price = appPrice;
        rating = appRating;
    }    
 
    /**
     * Create an app with the given name, author, and price that is not rated
     * @param appName the app name
     * @param appAuthor the app author
     * @param appPrice the price of the app (0 if the app is free)
     */
    public App(String appName, String appAuthor, double appPrice)
    {
        name = appName;
        author = appAuthor;
        price = appPrice;        
    }
 
    /**
     * @return the app name
     */
    public String getName()
    {
        return name;
    }
 
    /**
     * @return the app author
     */
    public String getAuthor()
    {
        return author;
    }
 
    /**
     * @return the app price
     */
    public double getPrice()
    {
        return price;
    }
 
    /**
     * Set the price of this app to the value given
     * @param newPrice new price for this app
     */
    public void setPrice(double newPrice)
    {
        if (newPrice >= 0) {
            price = newPrice;
        }
        else {
            System.out.println("Error: Price must be greater than or equal to 0");
        }
    }
 
    /**
     * @return true if this app is free, false otherwise
     */
    public boolean isFree()
    {   
        if(price == 0) {
            return true;
        }
        else {
            return false;
        }
    }
 
    /**
     * @return the app rating
     */
    public int getRating()
    {
        return rating;
    }
 
    /**
     * Set the rating of this app to the value given
     * @param newRating new rating for this app
     * Valid rating is 1-4
     */
    public void setRating(int newRating)
    {
        if((newRating >= 1) && (newRating <= 4)) {
            rating = newRating;
        }
        else if((newRating == 0) || (newRating > 4)) {
            System.out.println("Error: Valid rating range is 1-4.");
        }
    }
 
    /**
     * Reset the rating of this app to not rated
     */
    public void resetRating()
    {
        rating = 0;
    }
 
    /**
     * Increase the rating of this app by 1
     */
    public void increaseRating()
    {
        if(rating >= 0 && rating <= 3) {
            rating = rating + 1;
        }
        else if(rating == 0 || rating >= 4) {
            rating = rating;
        }
    }
 
    /**
     * Decrease the rating of this app by 1
     */
    public void decreaseRating()
    {
        if(rating == 1) {
            rating = 1;
        }
        else if(rating >= 2 && rating <= 4){
            rating = rating - 1;
        }
        else if(rating == 0){
             rating = rating;
        }
    }
 
    /**
     * Print information on this app
     */
    public void printAppInfo()
    {
        System.out.println("---------------------------------");
        System.out.println("App: " + name);
        System.out.println("Author: " + author);
        if(price == 0) {
            System.out.println("Price: FREE");
        }
        else{
        System.out.println("Price: $" + price);
        }
        if(rating == 0) {
            System.out.println("Rating: (not rated)");
        }
        else{
        System.out.println("Rating: " + rating);
        }
        System.out.println("---------------------------------");
    }
}

Where is the main method for starting the program's execution and calling methods to test them?

How do you execute the code for testing?

Sorry, I do not know how BlueJ works and can not help you with your problems in using it.

The main method is the first source code that I just posted

Are you sure there is a method named: main? I do not see it. Can you copy only the contents of the main method and paste it here?

I understand. I look for help online a lot but no one uses BlueJ so it doesn't translate the same. So, there is no main method. You are right. When you execute this code, does it run?

When you execute this code, does it run?

It will not execute without a main method.

Also the code in post#32 will not compile without errors.
The comment started on line 4 is not closed with the ending */

That sucks. I feel better about it now than I did an hour ago, so I'm happy for that. I fixed line 4. Not sure where the other errors are. I copied and pasted. Is there any way to upload screenshots? Also, can you help me with return emptyList? As I'm reading through the text, I just came across main method for the first time. Chapter 6.

help me with return emptyList

Why do you think the code does not return an empty list?
When you test the code with an unknown author, what does the method return?

tell me if this code is right for comparing strings

Yes, It uses the equals method which is the correct way to determine if two Strings are equal or not.
Do not use == or != when testing the contents of objects like Strings.

There is no need to have a separate test for not equal. Two Strings are either equal or not equal.
With an if statement:

  if(some test that returns true or false) {
      // execute here if true
  }else {
     // execute here if false
  }

compare get.appRating() with the parameter rating. Suggestions?

Post the code and the error messages.

it just hasn't been doing what I'm wanting it to do

What is the method supposed to do?
Please make a list of the steps the code needs to take to do what you want
and post them here. Each item in the list should be a simple step.

Note: The posted code does not have the comments that all the other posted code has.
The comments before the methods describe what the method is supposed to do, what arguments it will receive and what value it will return.

write a method called getNumAppsWithRating that takes an int parameter representing a rating, and returns the number of apps in the app store

Ok, what steps does the method need to take to do that?
Make a list of the steps and post it.

Where is the list of steps the method is supposed to do? Don't write any code yet.
You need to decide what the method is supposed to do BEFORE writing the code to do it.

Where are the comments before the method that describe what it is supposed to do?
For example:

    /**
     * Find an app by name
     * @param the name of the app being looked for
     * @return the name of the app if found
     */