我應該在哪里放置構造函數的通用代碼？

Question

我遇到的情況是，在一個類中我有2個構造函數，並且它們具有非常相似的代碼。 唯一的區別是對超類的構造函數的調用。 我應該把這個通用代碼放在哪里？ 我嘗試使用實例塊，但是使用實例塊時，我無法傳遞所需的參數。

同樣，這些字段是最終的。 因此將無法初始化構造函數以外的其他函數。

我的代碼如下：

private final SourceCache sourceCache;
private final ServiceCache serviceCache;
private final MethodCache methodCache;
private final ModelCache modelCache;
private final QueryFactory queryFactory;

public MetaDataPersistenceHandler(
    final Transaction transaction)
{
    super(transaction);
    this.transaction = transaction;
    this.sourceCache = new SourceCache(transaction);
    this.serviceCache = new ServiceCache(transaction);
    this.methodCache = new MethodCache(transaction);
    this.modelCache = new ModelCache(transaction);
    this.queryFactory = new QueryFactory();
    this.transaction.addQueryFactory(this.queryFactory);
}

public MetaDataPersistenceHandler(
    final Transaction transaction,
    final long fileSize)
{
    super(transaction, fileSize);
    this.transaction = transaction;
    this.sourceCache = new SourceCache(transaction);
    this.serviceCache = new ServiceCache(transaction);
    this.methodCache = new MethodCache(transaction);
    this.modelCache = new ModelCache(transaction);
    this.queryFactory = new QueryFactory();
    this.transaction.addQueryFactory(this.queryFactory);
}

Answer 1

如果您的實例字段是最終的，那么我將擁有不帶filesize的構造函數，只需調用第二個並傳遞0 / null值即可。

另外，為什么要在子類中分配事務？ 你不把它傳給父母嗎？

private final SourceCache sourceCache;
private final ServiceCache serviceCache;
private final MethodCache methodCache;
private final ModelCache modelCache;
private final QueryFactory queryFactory;

public MetaDataPersistenceHandler(
    final Transaction transaction)
{
    this(transaction, 0L); // Call the whole constructor below?
}

public MetaDataPersistenceHandler(
    final Transaction transaction,
    final long fileSize)
{
    super(transaction, fileSize);
    this.transaction = transaction; // Why are we setting this again?
    this.sourceCache = new SourceCache(transaction);
    this.serviceCache = new ServiceCache(transaction);
    this.methodCache = new MethodCache(transaction);
    this.modelCache = new ModelCache(transaction);
    this.queryFactory = new QueryFactory();
    this.transaction.addQueryFactory(this.queryFactory);
}

Answer 2

將其移至私有構造函數。

編輯：這是一個例子

public MetaDataPersistenceHandler(
        final Transaction transaction) {
    super(transaction);
    this.transaction = transaction;
    MetaDataPersistenceHandler();
}

public MetaDataPersistenceHandler(
        final Transaction transaction,
        final long fileSize) {
    super(transaction, fileSize);
    this.transaction = transaction;
    MetaDataPersistenceHandler();
}

private void MetaDataPersistenceHandler(){

    this.sourceCache = new SourceCache(transaction);
    this.serviceCache = new ServiceCache(transaction);
    this.methodCache = new MethodCache(transaction);
    this.modelCache = new ModelCache(transaction);
    this.queryFactory = new QueryFactory();
    this.transaction.addQueryFactory(this.queryFactory);        
}

Answer 3

更好的方法是使用Optional而不是0或null。

private final SourceCache sourceCache;
private final ServiceCache serviceCache;
private final MethodCache methodCache;
private final ModelCache modelCache;
private final QueryFactory queryFactory;

public MetaDataPersistenceHandler(
    final Transaction transaction)
{
    this(transaction, Optional.<Long>absent()); // Call the whole constructor below?
}

public MetaDataPersistenceHandler(
    final Transaction transaction,
    final Optional<Long> fileSize)
{
    super(transaction, (fileSize.isPresent() ? fileSize.get() : 0));
    this.transaction = transaction; // Why are we setting this again?
    this.sourceCache = new SourceCache(transaction);
    this.serviceCache = new ServiceCache(transaction);
    this.methodCache = new MethodCache(transaction);
    this.modelCache = new ModelCache(transaction);
    this.queryFactory = new QueryFactory();
    this.transaction.addQueryFactory(this.queryFactory);
}