Array out of bound Java

Question

I am working on a small program for school where i need to input an array. Every element in the array must be checked if the neighbours are smaller than the Element. If the neighbours are smaller --> This elements get an extra *

But i got problems with the boundaries, for example the first one and the last one. The first one has only one neighbour.

public class Tops {
    Scanner sc = new Scanner(System.in);

    public void calculate(){
        String number;
        ArrayList<String> numbers; //def’s, decl’s ArrayList 
        ArrayList<String> after;
        numbers = new ArrayList<>(); //creates numbers
        after = new ArrayList<>();
        number = sc.next();

        while (!"0".equals(number)) {  
            numbers.add(number); //initializes each ArrayList element
            number = sc.next();        
        }

       for (int i = 0; i < numbers.size(); i++) {             
                    if (Integer.parseInt(numbers.get(i)) > Integer.parseInt(numbers.get(i+1)) && Integer.parseInt(numbers.get(i)) > Integer.parseInt(numbers.get(i-1)) ){
                        String replace = numbers.get(i)+"*";
                        after.add(replace);
                    } else {
                        after.add(numbers.get(i));
                    } 
        }

        for(int i=0;i<after.size();i++){
            System.out.print(after.get(i)+ " ");
        } 
    }

    public static void main(String[] args) {
        new Tops().calculate();
    }

}

i hope you can help me

if your Loop runs with `i=numbers.size()-1` `i+1` is out of bounds. Change to `i < numbers.size()-1; ` — Jens, May 10 '17 at 10:46
Now sure why people don't give a try on Google before posting here :( — Mehraj Malik, May 10 '17 at 10:48
In addtion to @Jens, Exceptions gives you the line number of error. So you can see the source of the error. — Yusuf K., May 10 '17 at 10:48
Possible duplicate of [Java: Array Index Out of Bounds Exception](http://stackoverflow.com/questions/3951252/java-array-index-out-of-bounds-exception) — Jaroslaw Pawlak, May 10 '17 at 11:13
Possible duplicate of [What causes a java.lang.ArrayIndexOutOfBoundsException and how do I prevent it?](http://stackoverflow.com/questions/5554734/what-causes-a-java-lang-arrayindexoutofboundsexception-and-how-do-i-prevent-it) — AxelH, May 10 '17 at 11:14

Cristian Ramon-Cortes · Answer 1 · 2017-05-11T14:54:11.283

Since you need both neighbours of an element to be smaller to add an "*", you can skip the first and the last elements (because they are missing one of the neighbours).

Adapting your code with this consideration:

import java.util.ArrayList;
import java.util.Scanner;


public class Tops {

private static final Scanner INPUT_SCANNER = new Scanner(System.in);


public static void calculate() {
    // Initialize numbers
    ArrayList<String> numbers = new ArrayList<>();
    String number = INPUT_SCANNER.next();
    while (!"0".equals(number)) {
        numbers.add(number);
        number = INPUT_SCANNER.next();
    }

    // Check the neighbours
    ArrayList<String> after = new ArrayList<>();

    // Check first element
    if (numbers.get(0) > numbers.get(1)) {
        after.add(numbers.get(0) + "*");
    } else {
        after.add(numbers.get(0));
    }
    // Check other elements
    for (int i = 1; i < numbers.size() - 1; i++) {
        int previous = Integer.parseInt(numbers.get(i - 1));
        int current = Integer.parseInt(numbers.get(i));
        int next = Integer.parseInt(numbers.get(i + 1));

        String newElement = numbers.get(i);
        if (current > next && current > previous) {
            newElement = newElement + "*";
        }

        after.add(newElement);
    }
    // Check last element
    if (numbers.get(numbers.size() - 1) > numbers.get(numbers.size() - 2)) {
        after.add(numbers.get(numbers.size() - 1) + "*");
    } else {
        after.add(numbers.get(numbers.size() - 1));
    }
    after.add(numbers.get(numbers.size() - 1));

    // Show the result
    for (int i = 0; i < after.size(); i++) {
        System.out.print(after.get(i) + " ");
    }
}

public static void main(String[] args) {
    calculate();
}

}

Execution example:

INPUT: 1 2 3 2 1 0
OUTPUT: 1 2 3* 2 1

Notice that:

I have made your calculate method static since you do not have any non-static field on the Tops class
I have moved the numbers initialization to the begining of the method
The final numbers are added on the after list only once so you do not need to initialize it
To perform the comparison without converting the current number from string to int twice per loop iteration, I have moved the int formats out of the if comparison.

thank you for your answer, i didn't explain it well i think. The first and last can also have a * but only have one neighbour. — soepblik, May 10 '17 at 19:03
So instead of adding the element add an if check for each corner case. I'll update the answer — Cristian Ramon-Cortes, May 11 '17 at 14:51
@soepblik Please consider [accepting the answer](https://meta.stackexchange.com/questions/5234/how-does-accepting-an-answer-work) if it was useful. — Cristian Ramon-Cortes, Aug 08 '17 at 09:18

Array out of bound Java

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