Java中通用模板中的问题

Question

有人可以解释我的功能有什么问题，提前谢谢： 我有这些课程：

主

 public class Main {
        public static void main(String[] args) {
            String[] inArr = {"Hi", "Great", "Man", "Yeap", "Why"};
            int[] outArr = new int[5];

            Summer summing = new Summer();
            outArr = summing.sum(inArr, 2, new sumStringToInt(), outArr); //here problem

            for(int i = 0; i < outArr.length; i++){
                System.out.println(outArr[i] + " ");
            }

        }
    }

夏季

public class Summer{
    public <X,Y> Y[] sum(X[] inArr, Y first, SumFunction<Y,X> f, Y[] outArr){
        for(int i = 0; i < inArr.length; i++){
            outArr[i] = f.op(first, inArr[i]);
            first = outArr[i];
        }
        return outArr;
    }
}

和函数

public abstract class SumFunction<Y,X> {
public abstract Y op (Y y, X x);
}

sumStrinToInt

public class sumStringToInt  extends SumFunction<Integer, String>{
    public Integer op(Integer num, String s){
        return s.length() + num;
    }
}

我有一个错误：

The method sum(X[], Y, SumFunction<Y,X>, Y[]) in the type Summer is not applicable for the arguments (String[], int, sumStringToInt, int[])

Answer 1

原始人和仿制药不混合。

创建包装类型Integer的数组，它将编译：

Integer[] outArr = new Integer[5];

但请注意，您必须初始化数组元素，否则它们将为null。

Answer 2

您没有传递泛型参数，这导致它们是Object的类型。

summing.<String,Integer>sum(inArr, 2, new sumStringToInt(), outArr); 

Answer 3

在summing之前忘了<String,Integer>。请参阅下面的代码：

public class Main {
  public static void main(String[] args) {
    String[] inArr = {"Hi", "Great", "Man", "Yeap", "Why"};
    Integer [] outArr = new Integer [5];


Summer summing = new Summer();
outArr = summing.<String,Integer>sum(inArr, 2, new sumStringToInt(), outArr); //here problem

for(int i = 0; i < outArr.length; i++){
System.out.println(outArr[i] + " "); 
}   


}
}