Java: iterate through two arrays and using correct values

Question

Given 2 int arrays, a and b, return a new array length 2 containing, as much as will fit, the elements from a followed by the elements from b. The arrays may be any length, including 0, but there will be 2 or more elements available between the 2 arrays.

I'm wondering how to use a !=, and null. This is the first question I've used it in and I'm having a few errors. So my logic was to iterate through list a, until a null point, then go onto list b.

public int[] make2(int[] a, int[] b) {
      int[] answer = new int[2];
      for(int x = 0; x <= 1; x++){
          if(a[x] != null)
              answer[x] = a[x];
          else if (b[x != null]){
              answer[x] = b[x];
          }
      }

}

Something like this. Any tips on how to check for emptiness?

Answer 1

else if (b[x != null]){

Is not a valid statement, this will cause an error because (x != null) = true so is the same as else if (b[true]){ which does not make much sense.

Also, an empty array position of int will never be null but zero 0 instead.

Use this instead:

else if (b[x] != 0){

---

One more thing: as title says, use List to instead of array to have a variable number of elements:

public int[] make2(int[] a, int[] b) {
      List<Integer> answers = new ArrayList<Integer>();
      for(int x = 0; x <= 1; x++){    
          if(a[x] != 0) {             
              answers.add(a[x]);
          } else if (b[x] != 0) {
              answers.add(b[x]);
          }
      }
}

NOTES:

• use answers instead of answer, is better name for a List with multiple elements.
• take as usual to use ALWAYS { even if the statements inside are just one line
• your function is not valid since does not include return answer

---

EDIT

Sorry about the title, my mistake. It is arrays

In this case, just remember arrays are not resizeable, so in the moment of creating the array check maximum size:

int maxSize = a.length > b.length ? a.length : b.length;
int[] answer = new int[maxSize];

NOTE: you can use this variable in your loop to check max number...

---

EDIT2

An empty array position is represented by a 0? What about the example make2({}, {1, 2}) → {1, 2}, will a[0] != 0 skip it? because index 0 doesn't exist?

1. you cannot use make2({}, {1, 2}), not a valid statement in this case. To simulate this do:

   public static void main(String[] args) {
        int a[] = new int[2];
        int b[] = new int[2];
        b[0] = 1;
        b[1] = 2;
        make2(a,b);
        // if you want to see the output:
        System.out.println(Arrays.toString(make2(a,b)));
   }
   

2. It won't skip it, it will throw an ArrayIndexOutOfBoundsException, in this case, you must make you function failsafe, for this, just check lenghts before accessing the element to assert it will exist:

   public static int[] make2(int[] a, int[] b) {
         int[] answer = new int[2];
         for(int x = 0; x <= 1; x++){
             if(a.length >= x && a[x] != 0) { 
                 answer[x] = a[x];
             } else if (b.length >= x && b[x] != 0){
                 answer[x] = b[x];
             }
             // optional
             else {
                 answer[x] = -1; // this tells you there's no valid element!
             }
         }
         return answer;
   }
   

---

SOLUTION:

http://www.codingbat.com/prob/p143461 Here is a url to the question :D

Ok, you were missing the examples, all would be much clearer... This code pass all tests.

public int[] make2(int[] a, int[] b) {
  int[] answer = new int[2];       // create the array to fill
  int y = 0;                       // create a variable to check SECOND array position
  for(int x = 0; x <= 1; x++){     // make 2 iterations
      if(a.length > x) {           // if ARRAY a has a possible value at POSITION x
          answer[x] = a[x];        // put this value into answer
      } else if (b.length > y){    // if ARRAY a does not have possible value at POSITION x, 
                                   // check if ARRAY b has some possible value at POSITION y 
                                   // (remember y is the variable that keeps position of ARRAY b)
          answer[x] = b[y++];      // put b value at answer
      }
  }
  return answer;                   // return answer
}

Answer 2

You can check array if it string but your array is int. so you can use the following example

int arr[] = null;
if (arr != null) {
  System.out.println("array is null");
}


arr = new int[0];
if (arr.length != 0) {
  System.out.println("array is empty");
}

Answer 3

I have a few questions, before I suggest you some alternatives. 1. why are you declaring int[] answer = new int[2]; when question says 2 or more elements.

You should use :

List<int> stockList = new ArrayList<int>();

if(a[x] != null)
    stockList.add(a[x]);
else if (b[x] != null){
    stockList.add(b[x]);
}

int[] stockArr = new int[stockList.size()];
stockArr = stockList.toArray(stockArr);