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Thread: What is wrong with my ArrayList?

  1. #1
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    Question What is wrong with my ArrayList?

    Pleas help me!

    I have a problem with my ArrayList, I don't understand how the user input should be stored in the ArrayList and how I can print the ArrayList

    my code:

    import java.util.Scanner;
    import java.util.ArrayList;
     
    class Bank{
      double balance;
      //Account account;
      ArrayList<Account>account;
      CommandReader commandReader;
      boolean name;
     
      Bank(){
        commandReader = new CommandReader();
      }
     
      void run(){
        commandReader.run();
      }
     
      void enroll(String name){
        if(account.contains(name)){
          System.out.println("already enrolled");
        } else {
          account.add(new Account());
          account = new ArrayList<Account>();
        }
      }
     
      void deposit(String name, int amount){
        if (account.contains(name)){
          balance = balance + amount;
        } else {
          System.out.println("no such name "+name);
        }
      }
     
      void withdraw(String name, int amount){
        if(account.contains(name)){
          balance = balance - amount;
        } else {
          System.out.println("no such name "+name);
        }
      }
     
      void print(String name){
        System.out.println("Account of "+name);
        System.out.println("  balance: "+balance);
      }
     
      void printAll(){
        System.out.println(account);
      }
     
      void printRed(){
        if (balance < 0){
          System.out.println(account);
        } else {
          System.out.print("no negative balances");
        }
      }
     
      void interest (double rate){
     
      }
     
      public static void main(String[] args){
          new Bank().run();
      }
    }
     
    class CommandReader{
        Bank bank;
        Account account;
     
        /*
        CommandReader(Bank bank) {
            this.bank = bank;                      Why should this be here?
        }*/
     
        //CommandReader() {
        //    bank = new Bank();
        //}
     
        // @pre: input complies to specified format
        void run(){
            Scanner scanner;
            String command;
            String name;
            int amount;
            scanner = new Scanner(System.in);
            bank = new Bank();
            do{
                command = scanner.next().toLowerCase();
                if (command.equals("enroll")) {
                    name = scanner.next();
                    bank.enroll(name);
                } else if (command.equals("deposit")) {
                    name = scanner.next();
                    amount = scanner.nextInt();
                    bank.deposit(name, amount);
                } else if (command.equals("withdraw")) {
                    name = scanner.next();
                    amount = scanner.nextInt();
                    bank.withdraw(name, amount);
                } else if (command.equals("print")) {
                    name = scanner.next();
                    bank.print(name);
                } else if (command.equals("printall")) {
                    bank.printAll();
                } else if (command.equals("printred")) {
                    bank.printRed();
                } else if (command.equals("interest")) {
                    double rate = scanner.nextDouble();
                    bank.interest(rate);
                } else if (command.equals("stop")) { 
                    // do nothing
                } else {
                    System.out.println("unknown command");
                    // skip rest of line
                    scanner.nextLine();
                }
            } while (! command.equals("stop"));
        }
    }
     
    class Account{
      double balance;
      String name;
     
      Account(){
        balance = 0;
        this.name = name;
      }
     
      String getName(){
        return this.name;
      }
     
      void setName(String name){
       this.name = name; 
      }
    }


  2. #2
    Crazy Cat Lady KevinWorkman's Avatar
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    Default Re: What is wrong with my ArrayList?

    I would recommend creating a test program: can you write a simple main method that initializes an ArrayList, adds 10 Objects to it, then prints the ArrayList out? Which part of that simple program gives you trouble? Post it here in the form of an SSCCE, and we'll go from there.
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  3. #3
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    Default Re: What is wrong with my ArrayList?

    My program looks now like this:

     
    import java.util.Scanner;
    import java.util.ArrayList;
     
    class Bank{
      double balance;
      //Account account;
      ArrayList<Account>account = new ArrayList<Account>();
      CommandReader commandReader;
      boolean name;
     
      Bank(){
        commandReader = new CommandReader();
      }
     
      void run(){
        commandReader.run();
      }
     
      void enroll(String name){
        if(account.contains(name)){
          System.out.println("already enrolled");
        } else {
          account.add(new Account());
        }
      }
     
      void deposit(String name, int amount){
        if(account.contains(name)){
          balance = balance + amount;
        } else {
          System.out.println("no such name "+name);
        }
      }
     
      void withdraw(String name, int amount){
        if(account.contains(name)){
          balance = balance - amount;
        } else {
          System.out.println("no such name "+name);
        }
      }
     
      void print(String name){
        System.out.println("Account of "+name);
        System.out.println("  balance: "+balance);
      }
     
      void printAll(){
        System.out.println(account);
      }
     
      void printRed(){
        if (balance < 0){
          System.out.println(account);
        } else {
          System.out.print("no negative balances");
        }
      }
     
      void interest (double rate){
     
      }
     
      public static void main(String[] args){
          new Bank().run();
      }
    }
     
    class CommandReader{
        Bank bank;
        Account account;
     
        /*
        CommandReader(Bank bank) {
            this.bank = bank;
        }*/
     
        //CommandReader() {
        //    bank = new Bank();
        //}
     
        // @pre: input complies to specified format
        void run(){
            Scanner scanner;
            String command;
            String name;
            int amount;
            scanner = new Scanner(System.in);
            bank = new Bank();
            do{
                command = scanner.next().toLowerCase();
                if (command.equals("enroll")) {
                    name = scanner.next();
                    bank.enroll(name);
                } else if (command.equals("deposit")) {
                    name = scanner.next();
                    amount = scanner.nextInt();
                    bank.deposit(name, amount);
                } else if (command.equals("withdraw")) {
                    name = scanner.next();
                    amount = scanner.nextInt();
                    bank.withdraw(name, amount);
                } else if (command.equals("print")) {
                    name = scanner.next();
                    bank.print(name);
                } else if (command.equals("printall")) {
                    bank.printAll();
                } else if (command.equals("printred")) {
                    bank.printRed();
                } else if (command.equals("interest")) {
                    double rate = scanner.nextDouble();
                    bank.interest(rate);
                } else if (command.equals("stop")) { 
                    // do nothing
                } else {
                    System.out.println("unknown command");
                    // skip rest of line
                    scanner.nextLine();
                }
            } while (! command.equals("stop"));
        }
    }
     
    class Account{
      double balance;
      String name;
     
      Account(){
        balance = 0;
        this.name = name;
      }
     
      String getName(){
        return this.name;
      }
     
      void setName(String name){
       this.name = name; 
      }
    }

    But still it gives not the right outcome.

  4. #4
    Crazy Cat Lady KevinWorkman's Avatar
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    Default Re: What is wrong with my ArrayList?

    I would recommend creating a test program: can you write a simple main method that initializes an ArrayList, adds 10 Objects to it, then prints the ArrayList out? Which part of that simple program gives you trouble? Post it here in the form of an SSCCE, and we'll go from there.

    --- Update ---

    Your ArrayList holds accounts. Why are you passing a String into the contains() method?
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  5. #5
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    Default Re: What is wrong with my ArrayList?

    [/COLOR]Your ArrayList holds accounts. Why are you passing a String into the contains() method?[/QUOTE]

    I've put name in it, because when the user types a command like enroll "name" it should only make a new account when there is no account with the same name in the ArrayList?

    --- Update ---

    Quote Originally Posted by KevinWorkman View Post
    I would recommend creating a test program: can you write a simple main method that initializes an ArrayList, adds 10 Objects to it, then prints the ArrayList out? Which part of that simple program gives you trouble? Post it here in the form of an SSCCE, and we'll go from there.

    --- Update ---

    Your ArrayList holds accounts. Why are you passing a String into the contains() method?
    I've put name in it, because when the user types a command like enroll "name" it should only make a new account when there is no account with the same name in the ArrayList?

    import java.util.Scanner;
    import java.util.ArrayList;
     
    class BankTest{
      ArrayList<Account>account = new ArrayList<Account>();
      Scanner sc = new Scanner(System.in);
      String command, name;
     
      void run(){
        command=sc.next().toLowerCase();
        if (command.equals("enroll")){
            name=sc.next();
            enroll(name);         
        }
      }
     
      void enroll(String name){
        if(account.contains(name)){
          System.out.println("already enrolled");
        } else {
          account.add(new Account());
        }
      }
     
      void printAll(){
        /*if(account.contains()){
          System.out.println(account);
        }*/
        System.out.println(account);
      }
     
      public static void main(String[] args){
          new Bank().run();
      }
    }
     
    class Account{
      double balance;
      String name;
     
      Account(){
        balance = 0;
        this.name = name;
      }
     
      String getName(){
        return this.name;
      }
     
      void setName(String name){
       this.name = name; 
      }
    }

  6. #6
    Crazy Cat Lady KevinWorkman's Avatar
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    Default Re: What is wrong with my ArrayList?

    You're only ever adding in Accounts to your ArrayList. It will never contain a String.
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  7. #7
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    Default Re: What is wrong with my ArrayList?

    Quote Originally Posted by KevinWorkman View Post
    You're only ever adding in Accounts to your ArrayList. It will never contain a String.
    I don't know what you mean. Could you explain it with an example? I'm not so familiair with english terms, because I'm from Holland.

  8. #8
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    Default Re: What is wrong with my ArrayList?

    Your ArrayList only holds Accounts:

    ArrayList<Account>account = new ArrayList<Account>();

    You never add any Strings to that ArrayList. In fact, that would cause a compiler error. Yet you check whether the ArrayList holds a particular String, which it never will:

    void enroll(String name){
        if(account.contains(name)){
          System.out.println("already enrolled");
        } else {
          account.add(new Account());
        }
      }

    So that if statement will never evaluate to true. You need to rethink what you're doing here.
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  9. #9
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    Default Re: What is wrong with my ArrayList?

    Quote Originally Posted by KevinWorkman View Post
    Your ArrayList only holds Accounts:

    ArrayList<Account>account = new ArrayList<Account>();

    You never add any Strings to that ArrayList. In fact, that would cause a compiler error. Yet you check whether the ArrayList holds a particular String, which it never will:

    void enroll(String name){
        if(account.contains(name)){
          System.out.println("already enrolled");
        } else {
          account.add(new Account());
        }
      }

    So that if statement will never evaluate to true. You need to rethink what you're doing here.

    I understand what you say, but I just don't know how it works, could you give me a hint?

    what I have right now:

    void enroll(String name){
        if(account.equals(account)){
          System.out.println("already enrolled");
        } else {
          account.add(new Account());
        }
      }

  10. #10
    Crazy Cat Lady KevinWorkman's Avatar
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    Default Re: What is wrong with my ArrayList?

    You need to think about what exactly you're trying to do.

    Write a test program that programatically adds a few Accounts with hardcoded names to an ArrayList of Accounts. Then write a function that tests whether an Account with a certain name is in the ArrayList.
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