你可以传递一个int数组到Java中的泛型方法吗？ [英] Can you pass an int array to a generic method in java?

问题描述

我正在玩一些代码katas，并试图同时更好地理解java泛型。我有这样一个打印数组的方法，就像我喜欢看到它们一样，并且我有几个帮助器方法，它们接受'东西'和索引的数组，并返回索引上方或下方'东西'的数组这是一个二进制搜索算法）。

两个问题，

＃1我可以避免在splitBottom和splitTop中投射到T吗？它感觉不对，或者我正在以这种错误的方式去做（不要告诉我使用python或其他东西......））

＃2我必须编写单独的方法来处理基本数组吗？还是有更好的解决方案？

  public class Util {
 
 public static< T> void print（T [] array）{
 System.out.print（{）; 
 for（int i = 0; i< array.length; i ++）{
 System.out.print（array [i]）; 
 if（i< array.length  -  1）{
 System.out.print（，）; 
} 
} 
 System.out.println（}）; 
} 
 
 public static< T> T [] splitTop（T [] array，int index）{
 Object [] result = new Object [array.length  -  index  -  1]; 
 System.arraycopy（array，index + 1，result，0，result.length）; 
 return（T []）结果; 
} 
 
 public static< T> T [] splitBottom（T [] array，int index）{
 Object [] result = new Object [index]; 
 System.arraycopy（array，0，result，0，index）; 
 return（T []）结果; 
 
 
 public static void main（String [] args）{
 
 Integer [] integerArray = {1，2，3，4，5，6， 7，8，9，10}; 
 print（integerArray）; 
 print（splitBottom（integerArray，3））; 
 print（splitTop（integerArray，3））; 
 
 String [] stringArray = {one，two，three，four，five，six，seven，eight，nine， 十}; 
 print（stringArray）; 
 print（splitBottom（stringArray，3））; 
 print（splitTop（stringArray，3））; 
 
 int [] intArray = {1，2，3，4，5，6，7，8，9，10}; 
 // ??? 
} 
} 
  

解决方案

泛型不要以一致的方式处理原语。这是因为泛型不像C ++中的模板，它只是编译时添加到一个类中。

$ b 当通用编译完成后，最终会以Object []在上面的例子中作为实现类型。作为int []和byte []等，不要扩展Object []，即使所涉及的代码是相同的（即泛型不是模板），也不能互换使用它们。

唯一的类int []和Object []共享是Object。你可以把上面的方法Object写成类型（参见System.arraycopy，Array.getLength，Array.get，Array.set）。

I'm playing around with some code katas and trying to get a better understanding of java generics at the same time. I've got this little method that prints arrays like I like to see them and I have a couple of helper methods which accept an array of 'things' and an index and returns the array of the 'things' above or below the index (it's a binary search algorithm).

Two questions,

#1 Can i avoid the cast to T in splitBottom and splitTop? It doesn't feel right, or I'm going about this the wrong way (don't tell me to use python or something .. ;) )

#2 Do I have to write seperate methods to deal with primitive arrays or is there a better solution?

public class Util {

    public static <T> void print(T[] array) {
        System.out.print("{");
        for (int i = 0; i < array.length; i++) {
            System.out.print(array[i]);
            if (i < array.length - 1) {
                System.out.print(", ");
            }
        }
        System.out.println("}");
    }

    public static <T> T[] splitTop(T[] array, int index) {
        Object[] result = new Object[array.length - index - 1];
        System.arraycopy(array, index + 1, result, 0, result.length);
        return (T[]) result;
    }

    public static <T> T[] splitBottom(T[] array, int index) {
        Object[] result = new Object[index];
        System.arraycopy(array, 0, result, 0, index);
        return (T[]) result;
    }

    public static void main(String[] args) {

        Integer[] integerArray = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
        print(integerArray);
        print(splitBottom(integerArray, 3));
        print(splitTop(integerArray, 3));

        String[] stringArray = {"one", "two", "three", "four", "five", "six", "seven", "eight", "nine", "ten"};
        print(stringArray);
        print(splitBottom(stringArray, 3));
        print(splitTop(stringArray, 3));

        int[] intArray = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
        // ???
    }
}

解决方案

Generics don't handle primitives in a consistent fashion. This is because Generics are not like templates in C++, it is just a compile time addition to a single class.

When generic are compiled, you end up with Object[] in the above example as the implementing type. As int[] and byte[] etc, do not extend Object[] you cannot use them inter-changeably even if the code involved would be identical (again generics are not templates)

The only class int[] and Object[] share is Object. You can write the above methods Object as the type (see System.arraycopy, Array.getLength, Array.get, Array.set)

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