Java 8嵌套Lambda函数实现：如何传递两个参数获取数据？

You're on the right track with the part_number_function! For sales_function and quotes_function, we need to create nested functions: first accept a Part, then return another function that takes a condition ID and returns the corresponding BigDecimal value. Here's how to implement this cleanly:

Using Nested Lambda Expressions (Most Readable) #

This approach directly maps the chain of operations: retrieve the PartData for the given condition ID, then extract the sales/quotes value from it.

void go() {
    Part part = ...;
    int condition_id = ...;

    part_number_function = Part::getPart_number;
    String part_number = part_number_function.apply(part);

    // Define sales_function: Part -> (Integer -> BigDecimal)
    sales_function = partObj -> conditionId -> partObj.getData(conditionId).getSales();
    // Define quotes_function using the same pattern
    quotes_function = partObj -> conditionId -> partObj.getData(conditionId).getQuotes();

    BigDecimal sales = sales_function.apply(part).apply(condition_id);
    BigDecimal quotes = quotes_function.apply(part).apply(condition_id);
}

Breakdown: #

• sales_function is a Function<Part, Function<Integer, BigDecimal>>:
  1. Calling sales_function.apply(part) returns a Function<Integer, BigDecimal> bound to your specific part instance.
  2. Calling apply(condition_id) on that inner function uses part.getData(condition_id) to fetch the PartData, then calls getSales() to get the final value.

Alternative: Using Method References with andThen #

If you prefer method references over nested lambdas, you can chain the getData call with the getter method using Function.andThen(). A cast is needed here to help the compiler infer the functional interface type:

void go() {
    Part part = ...;
    int condition_id = ...;

    part_number_function = Part::getPart_number;
    String part_number = part_number_function.apply(part);

    sales_function = partObj -> ((Function<Integer, PartData>) partObj::getData).andThen(PartData::getSales);
    quotes_function = partObj -> ((Function<Integer, PartData>) partObj::getData).andThen(PartData::getQuotes);

    BigDecimal sales = sales_function.apply(part).apply(condition_id);
    BigDecimal quotes = quotes_function.apply(part).apply(condition_id);
}

Optional: Handle Null Values #

If getData(condition_id) might return null, add a null check to avoid NullPointerException using Optional:

sales_function = partObj -> conditionId -> Optional.ofNullable(partObj.getData(conditionId))
                                                  .map(PartData::getSales)
                                                  .orElse(BigDecimal.ZERO);

内容的提问来源于stack exchange，提问作者ryvantage