Question

抱歉，如果代码看起来很乱。

新手在这里。我试图让用户根据他们的输入删除App类型的对象，而ArrayList只接受类型＆＃39; App＆＃39;的对象。但是，我无法删除它，因为我在if语句中创建了一个App类型的对象，但我不知道如何访问它。有没有什么方法可以删除和编辑由其他if语句创建的对象if？

public static void main(String[] args) throws IOException {
    // TODO code application logic here



Scanner myScan = new Scanner(System.in);



System.out.println("Enter your option from the list below");
System.out.println("1.App Store");
System.out.println("2.Customer stuff");
int input = myScan.nextInt();

if (input == 1){
    wholeSystem();
}


}





public static void wholeSystem()

{
    boolean choice = true;
    int input2 = 0;
    Shop appStore = new Shop(new ArrayList<App>());  
    while (choice == true)

            {



    Scanner myScan2 = new Scanner(System.in);
    System.out.println("Enter another option from the list below");
    System.out.println("1. Add new App details");
    System.out.println("2. Delete App details");
    System.out.println("3. Edit App details");
    System.out.println("4. List App details");
    System.out.println("5. Search App details");
    System.out.println("6. Quit");
    input2 = myScan2.nextInt(); 

    if (input2 == 6)
    {
        System.out.println("You have exited.");
         break;
    }

    else if (input2 == 1)
    {
        System.out.println("You have selected feature "+input2+".");
        Scanner myScan3 = new Scanner(System.in);
        App myObj = new App();
        System.out.println("Please enter the app name:");
        myObj.setAppName(myScan3.nextLine());
        System.out.println("Please enter the developer name:");
        myObj.setDeveloperName(myScan3.nextLine());
        System.out.println("Please enter the app's function:");
        myObj.setAppFunction(myScan3.nextLine());
        System.out.println("Please enter the app's type");
        myObj.setType(myScan3.nextLine());
        System.out.println("Please enter the app's cost:");
        myObj.setCost(myScan3.nextInt());
        System.out.println("Please enter the app's popularity:");
        myObj.setPopularity(myScan3.nextInt());
        System.out.println(myObj.getAppName()+myObj.getDeveloperName());
        appStore.addApp(myObj);




File AppStore = new File("AppStore");        
try{

BufferedWriter out;

out = new BufferedWriter ( new FileWriter(AppStore,true));


out.write(myObj.getAppName());
out.newLine();
out.write(myObj.getDeveloperName());
out.newLine();
out.write(myObj.getAppFunction());
out.newLine();
out.write(myObj.getType());
out.newLine();
out.write (String.valueOf(myObj.getCost()) );
out.newLine();
out.write(String.valueOf(myObj.getPopularity()) );
out.newLine();
out.write("========================================================");
out.newLine();
//Close the output stream
out.close();
}
catch (Exception e){//Catch exception if any
  System.err.println("Error: " + e.getMessage());
        }    
    }

    else if (input2 == 2)
    {
        int choiceInput = 0;
        System.out.println("You have selected feature "+input2+". Which app do you want deleted?");
        // here's where I tried to remove an object 
        appStore.printApps();
        choiceInput = myScan2.nextInt();
        appStore.deleteApp(choiceInput); with user input

这是我创建ArrayList的商店类。公共类商店{

private ArrayList<App> apps = new ArrayList<App>();



public Shop(ArrayList apps)
{
    this.apps = apps;
}

public ArrayList<App> getApps(){return apps;}

public void setApps(ArrayList<App>apps){this.apps = apps;}

public void addApp(App app){apps.add(app);}

public void deleteApp(App app){apps.remove(app);}

Answer 1

如果我理解正确，您只需要在Shop类中添加另一种方法：

public void deleteApp(int index){apps.remove(index);}

现在你只支持通过对象引用删除，但底层的ArrayList也可以通过索引删除。如果您公开该接口，您的主代码将起作用...

编辑：我之前有Integer而不是int。这是一个Object，所以它会尝试删除匹配的对象。要通过索引删除，我需要使用int声明它，如果传入一个Integer，则使用Java box / unbox。

Answer 2

更改

public static void wholeSystem（）

签名：

public static List<App> wholeSystem()

然后：

List<App> appList = new ArrayList<App>();   
if (input == 1){
   appList = wholeSystem();
}

然后你可以在if（input == 1）block〜

之后删除anyApp

如果您尝试使用列表中的索引位置删除应用程序，请执行以下操作：

public void deleteApp(int index){
    App removedApp = apps.remove(index);
}

请注意，上面的remove方法也会返回Object，这样你就可以用它做任何你想做的事了〜

有没有办法从另一个if语句中删除由ArrayList中的if语句创建的对象？

2 个答案: