Reverse an Array using Java

Question

I filled an array with the numbers 1 to 10 using a for-loop. Now I need to fill a second array with the values of the first array, but upside down. So the second array has to be filled with 10 to 1.

I tried something but it fills the second array with just 1.

output is:

and it should be 1 2 3 4 5 6 7 8 9 10 10 9 8 7 6 5 4 3 2 1

package FillandTurn;

import java.util.Scanner;

/**
 *
 * @author Quinten
 */
public class FillandTurn {

    /**
     * @param args the command line arguments
     */
    Scanner scan = new Scanner(System.in);
    public static void main(String[] args) {
        // TODO code application logic here
        FillandTurn fill = new FillandTurn();
        fill.start();
    }

    public void start(){
        FillandTurn turn = FillandTurn();
        int[] array = turn.vullen();
        int[] array2 = turn.draaien(array);
    }
    public int[] fill(){
        int[] array = new int[10];
        int j = 0;
        for(int i = 0; i < array.length; i++ ){
            j++;
            array[i] = j;
        }


        for(int p = 0; p <= array.length-1; p++ ){
            System.out.println(array[p]);
        }

        return array;
    }
    public int[] turn(int[] array){
        int[] array2 = new int[10];
        for(int x = 0; x < array2.length; x++){
            for(int y = array.length-1; y >=0; y--){
                array2[x] = array[y];
            }
        }


        for(int p = 0; p <= array2.length-1; p++ ){
            System.out.println(array2[p]);
        }


       return array2;


    }

}

Any helps is appreciated!

`p <= array2.length-1` is equivalent to `p < array2.length` – Jan Dec 10 '15 at 19:16 — Jan, Dec 10 '15 at 19:16

score 0 · Answer 1 · answered Dec 10 '15 at 19:15

0

Have a for loop to fill the first array as stated, but then have a seperate for loop for the second array, which starts at the size of the first array, and decrements on each iteration, putting the elements into the new array

answered Dec 10 '15 at 19:15

kxdan

187
1
15

score 0 · Answer 2 · answered Dec 10 '15 at 19:20

Have you tried reading the array from the back to the front?

public int[] reverseArray(int[] array1) {
    int[] array2 = new int[array1.length];

    int pos = 0;

    for(int neg = array1.length; neg >= 0; neg--) {
        array2[pos] = array1[neg];
    }

    return array2;
}

This is a simple way, there is probably better ways to do this.

score 0 · Answer 3 · answered Dec 10 '15 at 19:23

When you copy an array you only need one loop. Using a nested loop means you are copying each value N times, or in fact the first value overwrites all the others.

You can do

class FillAndTurn {
    public static void main(String... args) {
        int[] array = new int[10];
        fill(array);
        int[] array2 = turn(array);
        IntStream.of(array).forEach(System.out::println);
        IntStream.of(array2).forEach(System.out::println);
    }

    static void fill(int[] array) {
        for (int i = 0; i < array.length; i++)
            array[i] = i + 1;
    }

    static int[] turn(int[] array) {
        int[] array2 = new int[array.length];
        for(int i = 0; i < array.length; i++)
            array2[array2.length - i - 1] = array[i];
        return array2;
    }
}

Reverse an Array using Java

3 Answers3