System.out.println("=== before transaction ===");
System.out.println(sourceAccount);
System.out.println(destinationAccount);
System.out.println("\n=== transfer 400 ===");
sourceAccount.transferTo(destinationAccount, 400);
System.out.println("\n=== after transaction ===");
System.out.println(sourceAccount);
System.out.println(destinationAccount);
}