Question

public class Bank {
    private ArrayList<Account> accounts;
    private int numberOfAccounts;

    public Bank() {
        numberOfAccounts = 0;
        accounts = new ArrayList<Account>();
    }

    public int getNumOfAccounts() {
        return numberOfAccounts;
    }

    public void addAccount(Account a) {
        numberOfAccounts++;
        accounts.add(a);
    }

    public Account findAccount(int id) {
        int index = id - 1;
        if (accounts.size() >= id){
            return accounts.get(index);
        }
        else return null;
    }

    public void addMonthlyInterest() {
        for (Account x : accounts) {
            x.addMonthlyInterest();
        }
    }

    public void removeAccount(Account a) {
        numberOfAccounts--;
        accounts.remove(a);
    }
}

因此，当我将帐户添加到ArrayList，然后检查大小时，它会一直告诉我其中没有任何内容。我使用.add()添加的方式有什么问题吗？

这是我的BankTest的一部分。我不确定要为testAddAccount（JUnit明智）使用什么，但我知道它们没有被添加，因为当我尝试查找帐户时，它们都不存在。

import static org.junit.Assert.*;
import static org.junit.Assert.assertEquals;

import java.util.ArrayList;

import org.junit.Test;

public class BankTest {
    private final ArrayList<Account> accounts = new ArrayList<Account>();
    private Bank bank = new Bank();
    private java.util.Random rand;
    // private static final double[] RATES;
    // private static final int[] TYPES;

    SavingsAccount sa = new SavingsAccount(0.034);
    CheckingAccount ca = new CheckingAccount(0.034, 100);
    CreditCardAccount cca = new CreditCardAccount(0.034, 100);

    @Test
    public void testAddAccount() {
        // Tests Bank.addAccount() by adding many random accounts to the bank.
        // SavingsAccount sa = new SavingsAccount(0.034);
        SavingsAccount sa = new SavingsAccount(0.034);
        CheckingAccount ca = new CheckingAccount(0.034, 100);
        CreditCardAccount cca = new CreditCardAccount(0.034, 100);
        bank.addAccount(sa);
        bank.addAccount(ca);
        bank.addAccount(cca);
        if (accounts.size() == 3){
            System.out.println("true");
        }else System.out.println("false");

    }

    @Test
    public void testFindAccount() {
        // Tests Bank.findAccount() by finding all existing accounts and
        // attempting to find some non-existing accounts.
        bank.addAccount(sa);
        bank.addAccount(ca);
        bank.addAccount(cca);

        int size = accounts.size();
        System.out.println(size);
        accounts.get(0);
        assertEquals(sa, bank.findAccount(1));
        assertEquals(ca, bank.findAccount(2));
        assertEquals(cca, bank.findAccount(3));

        assertNull(bank.findAccount(50));
        assertNull(bank.findAccount(80));
        assertNull(bank.findAccount(230));

    }

}

Answer 1

我需要看看你如何实例化和使用Bank对象，但我猜你的问题就在那里。每当您创建新银行时，帐户列表都会初始化 - 您是否在尝试访问帐户列表时创建新银行？

Answer 2

我会不手动跟踪＃/帐户。出于几个不同的原因，这是“糟糕的”。这是另一种选择：

public class Bank {
private ArrayList<Account> accounts;
// private int numberOfAccounts; // No!

public Bank() {
    // numberOfAccounts = 0; // No!
    accounts = new ArrayList<Account>();
}

public int getNumOfAccounts() {
    return accounts.size();
}

public void addAccount(Account a) {
    // numberOfAccounts++; // No!
    accounts.add(a);
}

Answer 3

你没有检查正确的ArrayList！你的代码：

// what is accounts variable for?? Get rid of it.
private final ArrayList<Account> accounts = new ArrayList<Account>(); 

private Bank bank = new Bank();
private java.util.Random rand;
// private static final double[] RATES;
// private static final int[] TYPES;

SavingsAccount sa = new SavingsAccount(0.034);
CheckingAccount ca = new CheckingAccount(0.034, 100);
CreditCardAccount cca = new CreditCardAccount(0.034, 100);

@Test
public void testAddAccount() {
    // Tests Bank.addAccount() by adding many random accounts to the bank.
    // SavingsAccount sa = new SavingsAccount(0.034);
    SavingsAccount sa = new SavingsAccount(0.034);
    CheckingAccount ca = new CheckingAccount(0.034, 100);
    CreditCardAccount cca = new CreditCardAccount(0.034, 100);
    bank.addAccount(sa);
    bank.addAccount(ca);
    bank.addAccount(cca);
    if (accounts.size() == 3){  // **** accounts.size()???
        System.out.println("true");
    }else System.out.println("false");

您正在检查accounts.size()，并且帐户是一个本地变量，并且不知道银行持有的帐户，即银行对象。 account.size（）应该是0，这完全合理。相反，为什么不检查bank变量所持有的大小呢？这就是为什么Bank有这种方法的原因：

    if (banks.getNumOfAccounts() == 3){
        System.out.println("true");
    }else System.out.println("false");

将Account对象添加到ArrayList

3 个答案: