java中的泛型方法，用于总结给定列表中的所有值，无论是String，int，double

How can I write this method?

我该怎么写这个方法?

public static <T> void adds(List<T> k,int i)
{
    T y;
    List<T> g = new ArrayList<T>();
    for(i=0;i<5;i++) {
        y+= k.get(i));}
    }    
}

What should I use for the sum?

我应该用什么来计算总和?

I have tried declaring a type T as a variable to place the sum within it.

我已经尝试将类型T声明为变量以将总和放入其中。

1 个解决方案

#1

You can use a generic method that takes a BinaryOperator<T> of the type to be summed and calls it to add in a reduce operation:

您可以使用一个泛型方法,该方法将要对的类型的BinaryOperator 求和,并将其调用以在reduce操作中添加:

public static <T> T sum(List<T> list, BinaryOperator<T> adder) {
    return list.stream().reduce(adder).get();
}

And you can use it like this:

你可以像这样使用它:

List<String> s = Arrays.asList("1", "2", "3");
sum(s, (s1, s2) -> String.valueOf(Double.parseDouble(s1) + Double.parseDouble(s2))); //"6.0"
sum(Arrays.asList(1, 2, 3, 4), (a, b) -> a + b); //10

This allows the method to be free of type-specific "addition" logic (so String list can be concatenated, numbers added, etc.

这允许该方法没有特定于类型的“添加”逻辑(因此可以连接字符串列表,添加数字等。

#1