How can I search for ArrayList elements in a Queue?

Question

I have an Arraylist containing accounts:

static List<Account> accounts = new ArrayList<>();

where an Account has these attributes:

private int accountId; 
private String name;
private String email;
private double balance;
private String date;

and a Queue of transactions

static Queue<Transaction> transactions = new LinkedList<Transaction>();

where a Transaction has the following attributes

private int transactionId;
private String type;
private double amount;
private String dateTime;

I want to use the accountId to search for all the transactions made with the specified accountId in my transactions' Queue .

How can I achieve this ?

Answer 1

Given an Account class as follows:

package test;

public class Account {
    private static int currentAccountId = 0;
    private int accountId;

    public Account() {
        this.accountId = ++currentAccountId;
    }

    @Override
    public String toString() {
        return String.valueOf(this.accountId);
    }
}

You should add a field of type Account to your Transaction class:

package test;

import java.util.Date;

public class Transaction {
    private static int currentTransactionId = 0;
    private final int transactionId;
    private final Account account;
    private final String type;
    private final double amount;
    private final Date dateTime;

    public Transaction(final Account account, final String type, final double amount) {
        this.account = account;
        this.type = type;
        this.amount = amount;
        this.dateTime = new Date();
        this.transactionId = ++currentTransactionId;
    }

    public int getTransactionId() {
        return this.transactionId;
    }

    public Account getAccount() {
        return this.account;
    }

    public String getType() {
        return this.type;
    }

    public double getAmount() {
        return this.amount;
    }

    public Date getDateTime() {
        return this.dateTime;
    }

    @Override
    public String toString() {
        return "Transaction: "
           + this.transactionId
           + "/ Account:"
           + this.account.toString()
           + " / Type:"
           + this.type
           + " / Amount:"
           + this.amount
           + " / Date:"
           + this.dateTime.toGMTString()
           + System.lineSeparator();
    }
}

Then you can search for an Account in your Queue by reference. Example with 3 accounts, 5 transactions, if you search for transactions related to account1:

package test;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.LinkedList;
import java.util.List;
import java.util.Queue;

public class Runner {

    public static void main(final String[] args) {
        List<Account> accounts = new ArrayList<Account>();
        Account account1 = new Account();
        Account account2 = new Account();
        Account account3 = new Account();
        accounts.add(account1);
        accounts.add(account2);
        accounts.add(account3);
        Queue<Transaction> transactions = new LinkedList<Transaction>();
        transactions.add(new Transaction(account1, "CREDIT", 10d));
        transactions.add(new Transaction(account1, "CREDIT", 20d));
        transactions.add(new Transaction(account2, "CREDIT", 5d));
        transactions.add(new Transaction(account3, "CREDIT", 8d));
        transactions.add(new Transaction(account1, "DEBIT", 3d));

        List<Transaction> account1Transactions = new ArrayList<Transaction>();
        for (Transaction transaction : transactions) {
            if (transaction.getAccount().equals(account1)) {
                account1Transactions.add(transaction);
            }
        }
        System.out.println(Arrays.toString(account1Transactions.toArray()));
    }

}

Running the program prints out the following output:

[Transaction: 1/ Account:1 / Type:CREDIT / Amount:10.0 / Date:15 Dec 2015 15:56:54 GMT
, Transaction: 2/ Account:1 / Type:CREDIT / Amount:20.0 / Date:15 Dec 2015  15:56:54 GMT
, Transaction: 5/ Account:1 / Type:DEBIT / Amount:3.0 / Date:15 Dec 2015 15:56:54 GMT
]

Which matches the 3 transactions related to account1.