Java 如何在函数接口/lambda调用中传递对象

所以，我有一段代码

public static void printStuff(Object[] stuffs, Function<?, String> func) {
    for(Object stuff : stuffs) {
        String stringStuff = func.apply(stuff);
        System.out.println(stringStuff);
        // or whatever, what is done with that String is not relevant
    }
    // ...

所以我肯定需要我的东西是Object[]，因为它是方法调用中不同类型的第一个常见超类

在编译方面，我得到：

MyClass.java:6: error: incompatible types: Object cannot be converted to CAP#1
        String stringStuff = func.apply(stuff);
                                        ^
  where CAP#1 is a fresh type-variable:
    CAP#1 extends Object from capture of ?

---

我的猜测是javac为我给函数的参数提供了一个解决方案，即使用：

public static <T> void printStuff(T[] stuffs, Function<T, String> func) {
    for(T stuff : stuffs) {
        // ....

---

一种解决办法是使用：

public static <T> void printStuff(T[] stuffs, Function<T, String> func) {
    for(T stuff : stuffs) {
        // ....

关于第一个代码：

public static void printStuff(Object[] stuffs, Function<?, String> func) {
    for(Object stuff : stuffs) {
        String stringStuff = func.apply(stuff);
        System.out.println(stringStuff);
        // or whatever, what is done with that String is not relevant
    }
}

或以一般方式：

public static <U> void printStuff(U[] stuffs, Function<? super U, String> func) {
    for(U stuff : stuffs) {
        String stringStuff = func.apply(stuff);
        System.out.println(stringStuff);
        // or whatever, what is done with that String is not relevant
    }
}

数组的类型必须等于函数的第一个类型参数或其子类。

对于第一个代码：

public static void printStuff(Object[] stuffs, Function<?, String> func) {
    for(Object stuff : stuffs) {
        String stringStuff = func.apply(stuff);
        System.out.println(stringStuff);
        // or whatever, what is done with that String is not relevant
    }
}

或以一般方式：

public static <U> void printStuff(U[] stuffs, Function<? super U, String> func) {
    for(U stuff : stuffs) {
        String stringStuff = func.apply(stuff);
        System.out.println(stringStuff);
        // or whatever, what is done with that String is not relevant
    }
}

---

数组的类型必须等于函数的第一个类型参数或其子类。

您不能公开静态void printtufft[]stuffs，Function func吗{和.nope，唉。看我的编辑你没有按照RC的建议更改你的签名。@Maaatt oops，读得太快了。确实有效-只要我不忘记更改内部for循环的类型。Daaang，我很确定类型变量数组是不可能的，尽管你不能公开静态void printtuff t[]stuff，Function func{和.nope，唉。看我的编辑你没有按照RC的建议更改你的签名。@Maaatt oops，读得太快了。确实有效-只要我不忘记更改内部for循环的类型。Daaang，我很确定类型变量数组是不可能的，尽管你已经搞定了。谢谢！你搞定了。谢谢！

public static void printStuff(Object[] stuffs, Function<Object, String> func)

public static <U> void printStuff(U[] stuffs, Function<? super U, String> func) {
    for(U stuff : stuffs) {
        String stringStuff = func.apply(stuff);
        System.out.println(stringStuff);
        // or whatever, what is done with that String is not relevant
    }
}