使用原始类型的成员变量，然后“按需”转换为适当的类型

Question

我在这里提出的问题与 Generic parameters declaration in static member

我发现自己使用原始类型在一个非泛型类中声明了几个成员变量（每个成员都有自己的不同类型），我想知道是否还有其他解决方案。

如果只有一个这样的变量，则可以使该类成为通用类，而无需使用原始类型。取而代之的是，鉴于此类类型的数量可能很多，使类成为泛型会很麻烦。

也可以通过使用通用方法提供此类变量来避免使用原始类型。但是，这将需要在每次调用时创建一个新实例。

以下是说明问题的代码：

import java.util.function.BiFunction;
import java.util.function.Consumer;

public class PreferencesForFruits {

interface Fruit{}
static class Banana implements Fruit {}
static class Apple implements Fruit {}

// a class describing the packaging of a fruit;
// it depends on the type of consumer of the fruit
static class FruitBox<F extends Fruit, C extends Consumer<F>> {
    // constructor (note that it doesn't accept wildcards, 
    // therefore its client must specify fixed types) 
    FruitBox(F f,C c) {}
}

// preferences for apples and bananas specified in two nested classes:
// 
public static class PrefsForApples<AC extends Consumer<Apple>> {
    // a functional object specifying 
    // how to pack a fruit for a customer
    BiFunction<Apple,AC,FruitBox<Apple,AC>> packingBiFunction = 
         (Apple a, AC ac) -> new FruitBox<Apple,AC>(a,ac);
}
//
public static class PrefsForBananas<BS extends Consumer<Banana>> {
    // ......
}

// convenience methods to obtained preferences;
// the argument is used here only to fix the generic type of the output
//
static <AC extends Consumer<Apple>> 
PrefsForApples<AC> newPrefsForApples(AC appleConsumer) {
    return new PrefsForApples<AC>();
}
//  
static <BC extends Consumer<Banana>> 
PrefsForBananas<BC> newPrefsForBananas(BC bananaSupplierDummy) {
    return new PrefsForBananas<BC>();
}

/*
 *  Now using fields of raw type to avoid creation of distinct instances  
 */

// Here are the raw type variables mentioned in the question:
private PrefsForApples prefsForApples;
private PrefsForBananas prefsForBananas;

// the convenience methods convert the raw type 
// to the required type 

<AC extends Consumer<Apple>> 
PrefsForApples<AC> prefsForApplesRaw(AC appleConsumer) {
    return (PrefsForApples<AC>) prefsForApples;
}

<BC extends Consumer<Banana>> 
PrefsForBananas<BC> prefsForBananasRaw(BC bananaSupplierDummy) {
    return (PrefsForBananas<BC>) prefsForBananas;
}