如何在我的程序中修复arrayindexoutofboundsexception错误 [英] How do I fix arrayindexoutofboundsexception ERROR in my program

问题描述

Functional  programming  languages  have  a  concept called map that  takes  a  function  and  an  array  as  parameters,  and  it  returns  the  array  produced  by  applying  the  function  to  every  element  of  the  original  array.    Given  that  our  recent  introduction  to  the edu.psu.cmpsc221.Function interface used static members, our map function will also be static and will have the following signature: 

public static <R, D> R[] map(Function<R, D> function, D[] array)

The syntax for this generic function is slightly different from the syntax of the other Java generics that we have seen in class (there is an additional pair of type variables that follows the static keyword).  This is the syntax Java uses for a static generic method. 

To help clarify whatmapis doing, a few example uses are provided:
// Example 1
Function<Integer, Integer> function = new CalculateSuccessor();
Integer[] integerArray = {1, 3, 4, 2, 5};
PrintArray(map(function, integerArray)); // map returns {2, 4, 5, 3, 6}

// Example 2
Function<Integer, String> anotherFunction = new CalculateLength();
String[] stringArray = { "Java", "C++", "Smalltalk" };
PrintArray(map(anotherFunction, stringArray)); // map returns {4, 3, 9}

// Example 3
Function<Double, Double> tripleFunction = new CalculateTriple();
Double[] doubleArray = { 2.0, 4.0, 5.0, 1.0 };
PrintArray(map(tripleFunction, doubleArray)); // map returns {6.0, 12.0, 15.0, 3.0}

Please note that while the solution is actually quite short, this is a challenging problem because Java willlikely get in your way and prevent you from implementing "obvious" solutions (recall that Java generics areknown to not play nicely with arrays). 

我尝试过：

What I have tried:

public static void main(String[] args)
{
    Function<Integer, Integer> function0 = new CalculateSuccessor();
    Integer[] integerArray = {1,3,4,2,5};      //creating a Integer array
    PrintArray(map(function0, integerArray)); 

    Function<Integer, String> function1 = new CalculateLength(); 
    String[] stringArray = {"Java", "C++", "Smalltalk"};
    PrintArray(map(function1, stringArray));                       
        
    Function<Double, Double> function2 = new CalculateTriple(); 
    // Double[] doubleArray = {2.0,4.0,5.0,1.0};                      
    Double[] doubleArray = { };  // ERROR HERE THIS NEED TO BE FIX
    PrintArray(map(function2, doubleArray)); 
}

@SuppressWarnings("unchecked")
public static <R, D> R[] map(Function<R, D> function, D[] array )
{
    R[] returnArray = (R[])Array.newInstance(function.apply(array[0]).getClass(), array.length);  // ERROR HERE THIS NEED TO BE FIX
    for(int i = 0;i < array.length; i++)               
    {
       returnArray[i] = function.apply(array[i]);
    }
       return returnArray; 
}

推荐答案

查看你的数组：

Look at your array:

Double[] doubleArray = { };

它不包含任何元素。

所以当你尝试使用其中任何一个时：

It contains no elements.
So when you try to use any of them:

function.apply(array[0])

您将始终获得索引超出范围的问题。你需要做两件事：

1）检查数组的大小，并确保它在你尝试处理之前包含数据。

2）设置你的数组实际包含一些数据......

You will always get an index out of bounds problem. YOu need to do two things:
1) Check the size of the array, and make sure it contains data before you try to process it.
2) Set up your array to actually contain some data...

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