How to compare and sort objects by property (using customized comparator)

Example: sort a bank account by its balance

public class BankAccount implements Comparable<BankAccount> {
	int accountNo;
	double balance;
	public BankAccount(int an, double b)
		this.accountNo = an;
		this.balance = b;
	public void setBalance(double b)
		this.balance = b;
	public double getBalance()
		return this.balance;
	public int compareTo(BankAccount arg0) {
		// TODO Auto-generated method stub
		return (int) (this.getBalance() - arg0.getBalance());
		//return + if this is greater, other wise -, 0 if this = arg0


//main program
import java.util.ArrayList;
import java.util.Collections;

public class BankAccountTester {
	public static void main (String[] args)
		final int NO_OF_ACCOUNTS = 10;
		ArrayList<BankAccount> bankAccountList = new ArrayList<BankAccount>();
		//generate some bank account with random balance and add to the arraylist of bankaccount
		for (int i = 0; i < NO_OF_ACCOUNTS; i++)
			bankAccountList.add(new BankAccount(i, Math.random()*1000));
		//using the natual compareTo method in bankAccountList to sort
		/*Can also use external comparator method, which is more flexiable, meaning you can compare any two objects without modifying the source code even if they are not comparable */
		Collections.sort(bankAccountList, new Comparator<BankAccount>() {
		    public int compare(BankAccount one, BankAccount other) {
		        return (int)(one.getBalance()- other.getBalance());
		for (BankAccount b : bankAccountList)
		//read as for every bankAccount b in the bankAccountList
			System.out.println("Accout No." + b.getAccountNo() + " Balance :" + b.getBalance()); 


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s