bankaccount.java

public class BankAccount {
    public double balance;

    public BankAccount(){
        this.balance = 0;
    }

    public void deposit(double deposit){
        this.balance = this.balance + deposit;
    }

    public void withdraw(double withdraw){
        this.balance = this.balance - withdraw;
    }

    public double getBalance(){
        return this.balance;
    }
}

banktester.java

public class BankAccountTester {
    public static void main(String[] args){
        BankAccount account = new BankAccount();
        account.deposit(1000);
        account.withdraw(500);
        account.withdraw(400);

        System.out.println(account.getBalance());
    }
}