Simplify decision whether to use one object or another in Java

user_478406 0
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I have a Transaction class which looks like this:

public class Transaction {

  private Transaction parentTransaction;
  private long amount;
  private String orderNumber;
}

So it has a field which points to another Transaction.

There is also a method like this:

public void build(Transaction transaction) {
    final long amount = transaction.getParentTransaction() == null ? transaction.getAmount() : transaction.getParentTransaction().getAmount();
    final String orderNumber = transaction.getParentTransaction() == null ? transaction.getOrderNumber() : transaction.getParentTransaction().getOrderNumber();
    // same pattern follows for more fields...


    // do other stuff...
}

Depending on whether a parentTransaction exists, e.g. the amount field shall be used from the parentTransaction or the transaction. What I don't like about this approach is the repetitive usage of the transaction.getParentTransaction() == null ? ... term.

Is there some pattern or apporach how I could avoid this?

java
4 Answers

Optional is an option, but I think there is a much simpler solution:

public void build(Transaction transaction) {
    Transaction buildFrom = transaction.getParentTransaction() == null ? transaction : transaction.getParentTransaction();
    ...
    String orderNumber = buildFrom.getOrderNumber();

If you don't like that mix of abstractions, you can go one step further and put that ? : line into a small helper method.

user_15311240

try Optional as suggested by others:

public void build(Transaction transaction) {
        
        Transaction parentTransactionElseTransaction = Optional.of(transaction)
                .map(t -> t.getParentTransaction())
                .orElse(transaction);

        final long amount = parentTransactionElseTransaction.getAmount();
        final String orderNumber = parentTransactionElseTransaction.getOrderNumber();

        // same pattern follows for more fields...
        // do other stuff...
    }
user_12115470

Use some minor refactoring with Optional:

public void build(Transaction transaction) {
    Transaction t = Optional.of(transaction).map(Transaction::getParent).orElse(transaction);
    long amount = t.getAmount(); 
    String orderNumber = t.getOrderNumber();
    // etc
}
user_2561960 
public void build(Transaction transaction) {
        final long amount = Optional.ofNullable(transaction.getParentTransaction()).orElse(transaction).getAmount();
        final String orderNumber = Optional.ofNullable(transaction.getParentTransaction()).orElse(transaction).getOrderNumber();
        // same pattern follows for more fields...


        // do other stuff...
    }

Can use Optional.ofNullable().orElse() here

user_77671140
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