I'm trying two write a method that each element in the new array corresponds to the difference of two adjacent numbers in the argument list. And the method should return a new array. I have written the method below but I have got this error Index 0 out of bounds for length 0.

int [] diff(int [] arr){
    int element;
    int [] newArr = new int[0];

    for(int i = 0; i < arr.length; i  ){
        element = arr[i] - arr[i 1];
        newArr [i] = element;

    }

    return newArr;
}

CodePudding user response：

the for loop i should be like less than arr.length-1 as you are accessing arr[i 1] so on last iteration i 1 becomes out of bounds.

CodePudding user response：

By subtracting the elements of an array with n elements from each other, an array with n-1 elements is obtained.

class Test {
    public static void main(String[] args) {
        // The original array contains n elements.
        int[] original = new int[] {4, 2, 6, 1, 9, 5};
        // The resulting array contains n-1 elements.
        int[] result = new int[original.length - 1];

        result = diff(original);
        print(result);
    }
    
    public static void print(int[] array ) {
        for(int i = 0 ; i < array.length ;   i) {
            System.out.println("Array["   i   "]: "   array[i]);
        }
    }

    public static int [] diff(int [] array){
        // The resulting array contains n-1 elements.
        int[] newArray = new int[array.length - 1];
        
        for(int i = 0; i < array.length - 1; i  ){
            newArray[i] = array[i] - array[i 1];
        }
        
        return newArray;
    }
}

The result:

Array[0]: 2
Array[1]: -4
Array[2]: 5
Array[3]: -8
Array[4]: 4

CodePudding user response：

In your code newArr initialise to 0 length. That's why it returns index out of bound when adding element to it. Try below code,

int[] diff(int []arr){

    int element;
    int [] newArr = new int[arr.length-1];

    for(int i = 1; i < arr.length; i  ){
        element = arr[i-1] - arr[i];
        newArr [i-1] = element;

    }
    return newArr;
}

CodePudding user response：

If you look with more precision your code you'll see an obvious error. Don't worry with time you won't do that error again ;)

int [] diff(int [] arr){
int element;
int [] newArr = new int[0];

for(int i = 0; i < arr.length; i  ){
    element = arr[i] - arr[i 1];
    newArr [i] = element;

}    
return newArr;

}

Just look your loop if I translate that in english it will mean "For Each i from 0 to the length of the array"

element = arr[i] - arr[i 1];

The final i-th term will be arr.length-1. So why you check the arr[arr.length] ? In an array of length n the indice is 0,1,...,n-1. Not n

CodePudding user response：

For any array of size N, there will be N-1 differences. Here is a Streams solution that provides the required result.

int[] s = {10,8,2,9,3,4};
int[] result = diff(s);
System.out.println(Arrays.toString(result));

prints

[2, 6, -7, 6, -1]

• Iterates over the array and places the adjacent value differences on the stream. Then collects them in an array.
• A valid array of length >= 2 is required, otherwise an exception is thrown.

public static int [] diff(int [] arr) {
      if (arr == null || arr.length < 2) {
          throw new IllegalArgumentException("Invalid array for method.");
      }
      return IntStream.range(0, arr.length-1)
                .map(i->arr[i] - arr[i 1])
                .toArray();
    }       
}

CodePudding user response：

Your code contains three errors.

1. int [] newArr = new int[0];
2. i < arr.length
3. arr[i] - arr[i 1];

Below is an updated version of your code to address those three problems.

import java.util.*;

public class Main{
   static int [] diff(int [] arr){
      int element;
      int [] newArr = new int[arr.length-1];

      for(int i = 0; i < arr.length-1; i  ){
          element = Math.abs(arr[i] - arr[i 1]);
          newArr [i] = element;

      }
      return newArr;
   }

    public static void main(String[] args) {
        int[] a = {1,5,8,15};
        System.out.println(Arrays.toString(diff(a)));
    }
}

Output:

[4, 3, 7]