Java: moving items in array

Question

I\'m looking to move things around within an Array.

I want to be able to move the last item within the given Array to a spot while moving those in the current locati

Answer 1

Another short and quick solution based on System.arraycopy:

System.arraycopy(array, insert, array, insert+1, array.length-insert-1);

The array content is "pushed to the right" from index "insert".

Here's some demonstration code:

int[] array = {1,2,3,4,5};
int insert = 2;
int last = array[array.length-1];
System.arraycopy(array, insert, array, insert+1, array.length-insert-1);
array[insert] = last;
for (int value:array) System.out.println(value);

Answer 2

you could do like this:

char arr1[]=new arr1[5]; // arr1 contains a,b,c,d,e in order
char arr2[]=new arr2[5];

for(int i=0;i<arr1.length;i++) {       // copy contents to arr2
   arr2[i]=arr1[i];
}

for(int i=0,j=4;i<arr1.length;i++) {
  arr2[i]=arr1[4];
  arr2[i+1]=arr1[4];
  arr2[i+2]=arr1[i+1];
  arr2[i+3]=arr1[i+2];
  arr2[i+4]=arr1[i+3];
}

for(int i=0;arr2.length;i++) {          // Final result
  System.out.println(arr[i]+" ");
}

Answer 3

Here's a more efficient and concise solution, relying on the natively implemented System.arraycopy:

public static void moveLastup(String[] arr, int pos) {
    String last = arr[arr.length-1];

    // Copy sub-array starting at pos to pos+1
    System.arraycopy(arr, pos, arr, pos + 1, arr.length - pos - 1);

    arr[pos] = last;
}

And some test code:

public static void main(String[] args) {
    String[] test = { "one", "two", "three", "four", "five" };

    // Move "five" to index 2
    moveLastup(test, 2);

    // [one, two, five, three, four]
    System.out.println(Arrays.toString(test));
}

---

Regarding your edit: You're working with and modifying the original array. If you want to "start over" in each moveLastup you need to work on a copy. This snippet prints what you want:

String[] list = { "a", "b", "c", "d", "e" };

for (int pos = 0; pos < list.length; pos++) {
    String[] tmpCopy = list.clone();
    moveLastup(tmpCopy, pos);
    showList(tmpCopy);
}

Output:

[e, a, b, c, d]
[a,e, b, c, d]
[a, b,e, c, d]
[a, b, c,e, d]
[a, b, c, d,e]

Answer 4

I know the question is about Arrays - don't wanna start a discussion about performance "versus" issues and "why I'm using pure array" - but for those using List I think this might be useful.

java.util.Collections.rotate method. Yeah, the name is weird, by check it out a part of the javadoc:

Note that this method can usefully be applied to sublists to move one or more elements within a list while preserving the order of the remaining elements. For example, the following idiom moves the element at index j forward to position k (which must be greater than or equal to j):

    Collections.rotate(list.subList(j, k+1), -1);

To make this concrete, suppose list comprises [a, b, c, d, e]. To move the element at index 1 (b) forward two positions, perform the following invocation:

    Collections.rotate(l.subList(1, 4), -1);

The resulting list is [a, c, d, b, e].

To move more than one element forward, increase the absolute value of the rotation distance. To move elements backward, use a positive shift distance.

public void moveElement(List list, int a, int b) {
    // forward or backward
    int direction = a > b ? 1 : -1;
    // always from minor to major to subList
    int minor = a < b ? a : b;
    int major = b > a ? b : a;
    Collections.rotate(list.subList(minor, major + 1), direction);
}

Answer 5

First of all, in your code you do

for (int x = stuff.length-1; x > pos; x--)  

where pos is not even defined, I suggest on changing it to position. second of all, change the "list" to "stuff".

Modified, working code:

public static void moveLastup(String[] stuff, int position) 
    {
        String y = stuff[stuff.length-1];

        for (int x = stuff.length-1; x > position; x--)  
            stuff[x] = stuff[x-1];

        stuff[position] = y;
    }

Answer 6

Any particular reason you're not using a List<String> instead of String[]? It'll make these type of operations easier. With an ArrayList<String>, all you need is:

list.add(3, list.remove(list.size() - 1));

Or even shorter if you used a LinkedList<String>:

list.add(3, list.removeLast());

Here's a more complete example based on yours:

LinkedList<String> list = new LinkedList<String>();
list.addAll(Arrays.asList("a", "b", "c", "d", "e"));
list.add(3, list.removeLast());
System.out.println(list); // prints "[a, b, c, e, d]"