java - 如何在 BiConsumer lambda 函数中获取 "Object cannot be converted"？

Question

我有一个类(Filter)，它有几个变量:

class Filter {
    Integer intVal;
    Double doubleVal;
    String strVal;

    public Integer getIntVal() {
        return intVal;
    }

    public void setIntVal(Integer intVal) {
        this.intVal = intVal;
    }

    public Double getDoubleVal() {
        return doubleVal;
    }

    public void setDoubleVal(Double doubleVal) {
        this.doubleVal = doubleVal;
    }

    public String getStrVal() {
        return strVal;
    }

    public void setStrVal(String strVal) {
        this.strVal = strVal;
    }
}

还有一个类 (Handler)，需要包含 lambda Function 和 BiConsumer 来获取和设置值:

class Handler {
    Function<Filter, Object> getter;
    BiConsumer<Filter, Object> setter;
    public Handler(Function<Filter, Object> getter, BiConsumer<Filter, Object> setter) {
        this.getter = getter;
        this.setter = setter;
    }
}

(我使用了 BiConsumer 因为这个答案: https://stackoverflow.com/a/27759997/963076 )。

实现如下:

Filter filter = new Filter();

Handler handler1 = new Handler(Filter::getIntVal, Filter::setIntVal);
Object o = handler1.getter.apply(filter);
handler1.setter.accept(filter, o);
Handler handler2 = new Handler(Filter::getDoubleVal, Filter::setDoubleVal);
Handler handler3 = new Handler(Filter::getStrVal, Filter::setStrVal);

但是 setter 不起作用。编译器抛出错误:

error: incompatible types: invalid method reference
Handler handler1 = new Handler(Filter::getIntVal, Filter::setIntVal);
incompatible types: Object cannot be converted to Integer

error: incompatible types: invalid method reference
Handler handler2 = new Handler(Filter::getDoubleVal, Filter::setDoubleVal);
incompatible types: Object cannot be converted to Double

error: incompatible types: invalid method reference
Handler handler3 = new Handler(Filter::getStrVal, Filter::setStrVal);
incompatible types: Object cannot be converted to String

因此，BiConsumer 无法将 Object 强制转换为 String 等。那么我该如何解决这个问题呢？我该如何编写此代码以便可以使用 lambda 函数设置 Filter 的值？

很确定答案与泛型有关，有时我很难理解它。

Answer 1

生成你的处理程序

class Handler<E> {
    Function<Filter, E> getter;
    BiConsumer<Filter, E> setter;
    public Handler(Function<Filter, E> getter, BiConsumer<Filter, E> setter) {
        this.getter = getter;
        this.setter = setter;
    }
}

这是示例用法

    Handler<Integer> handler1 = new Handler<>(Filter::getIntVal, Filter::setIntVal);
    Integer i1 = handler1.getter.apply(filter);
    handler1.setter.accept(filter, i1);