Array – Java

Very basic way to use java array –

  1. You can either use array declaration or array literal (but only when you declare and affect the variable right away, array literals cannot be used for re-assigning an array).For primitive types:
    int[] myIntArray = new int[3];
    int[] myIntArray = {1,2,3};
    int[] myIntArray = new int[]{1,2,3};

    For classes, for example String, it’s the same:

    String[] myStringArray = new String[3];
    String[] myStringArray = {"a","b","c"};
    String[] myStringArray = new String[]{"a","b","c"};
  2. Array length –
  3. Looping an array
    for(int k =0; k <myIntArray.length; k++) {
    for(int value:myIntArray) {
  4. Copy an array
    int[] B = Arrays.copyOf(A, j + 1);
    – copy array element from 0 to j+1
  5. ArrayList
    List<Integer> b = new ArrayList<Integer>();
    if (s.contains(value)) {
    } else {
  6.  // Sort array elements
  7. Boolean[] vis = new Boolean[n];
    Arrays.fill(vis, false);
  8. If an array or list collection has only primitive type then we can directly print it like-
    System.out.println( list);
    No need to use toString method.
    If we have a list of custom class then we need to override toString method in that class like here
  9. Create an ArrayList from another ArrayList. SO
    myObject = new ArrayList<Object>(myTempObject);
  10. Copy an array and convert it to String –
    messageChars = Arrays.copyOf(messageChars, messageChars.length – spaceCount);
    return new String(messageChars);
  11. Removing an element from the arraylist (or any Java collection) while iterating with any undesired affect. SO
    List<String> list = new ArrayList<>();
    // This is a clever way to create the iterator and call iterator.hasNext() like
    // you would do in a while-loop. It would be the same as doing:
    //     Iterator<String> iterator = list.iterator();
    //     while (iterator.hasNext()) {
    for (Iterator<String> iterator = list.iterator(); iterator.hasNext();) {
        String string =;
        if (string.isEmpty()) {
            // Remove the current element from the iterator and the list.


         // Sort odd number in descending order
        Arrays.sort(arr, 0, k,Collections.reverseOrder());
        // Sort even number in ascending order
        Arrays.sort(arr, k, n);



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