Iterate through an array in backwards direction, decreasing counter without using an if statement. Inverse of a modulus

Question

I have an array and two buttons ( Next and Previous ). When you click on the next button the mCurrent index updates(++) and the Cursor points to the next item in the list, and the opposite for the previous button.

String[] fruits = {"Pineaple", "Orange", "Banana", "Apple"};
int mCurrentIndex = 0;

This is the event handlers for the buttons:

 nextButton.setOnClickListener(new View.OnClickListener() {

     @Override
     public void onClick(View view) {
         mCurrentIndex = (mCurrentIndex + 1) % fruits.length;
         updateFruit();
     }
 });



prevButton.setOnClickListener(new View.OnClickListener() {


 @Override
    public void onClick(View view) {
        mCurrentIndex = (mCurrentIndex - 1);
        if(mCurrentIndex < 0){
            mCurrentIndex = fruits.length - 1;
        }
        updateFruit();
    }

 });

The code is working normal. But I want to find out whether there could be a way to refactor the previousButton code to be like the nextButton code(Making it shorter), by eliminating the if statement and replacing with something like inverse of a modulus (that is if it exists) and it will still work the same.

In each case the mCurrentIndex is reset when it reaches the end of the array.

Answer 1

The code is working normal. But I want to find out whether there could be a way to refactor the previousButton code to be like the nextButton code(Making it shorter), by eliminating the if statement and replacing with something like inverse of a modulus (that is if it exists) and it will still work the same.

mCurrentIndex = (mCurrentIndex + fruits.length - 1) % fruits.length;

should do that

Answer 2

I think you can use

public void onClick(View view) {
    mCurrentIndex = (fruits.length + (mCurrentIndex - 1)) % fruits.length;
    updateFruit();
}

Answer 3

Use one method,

  updateFuit(int refIndex) {
       mCurrentIndex = (mCurrentIndex + refIndex) % fruits.length;
       // Do rest of the updates..
  }

For buttons,

 nextButton.setOnClickListener(new View.OnClickListener() {
   @Override
   public void onClick(View view) {
        updateFruit(1);
   }
 });

 prevButton.setOnClickListener(new View.OnClickListener() {
  @Override
  public void onClick(View view) {
        updateFruit(fruits.length - 1);
  });