Effective swapping of elements of an array in Java

Question

I am wondering if there is a more efficient way of swapping two elements in an Array  than doing something like this   String temp   arr 1   arr 1    arr 2   arr 2    temp    Well  this is obviously not bad or even wrong  but I need to swap very often so I am interested if there are any Libs or something that provide a more efficient way to do this

User · Answer

Incredibly late to the party  my apologies  but a more generic solution than those provided here can be implemented  will work with primitives and non-primitives alike    public static void swap final Object array  final int i  final int j        final Object atI   Array get array  i       Array set array  i  Array get array  j        Array set array  j  atI       You lose compile-time safety  but it should do the trick   Note I  You ll get a NullPointerException if the given array is null  an IllegalArgumentException if the given array is not an array  and an ArrayIndexOutOfBoundsException if either of the indices aren t valid for the given array   Note II  Having separate methods for this for every array type  Object   and all primitive types  would be more performant  using the other approaches given here  since this requires some boxing unboxing   But it d also be a whole lot more code to write maintain

User · Answer

Use Collections swap and Arrays asList   Collections swap Arrays asList arr   i  j

User · Answer

This is just  quot hack quot  style method  int d       new int n  n    static int swap int a  int b      return a         in main class -- gt    d i  j   1    swap d i  j   d i  j    d i  j   1

User · Answer

first of all you shouldn t write for  int k   0  k    lt    data length   - 1    k   because the  lt  is until the k is smaller the length -1  and then the loop will run until the last position in the array and won t get the last place in the array  so you can fix it by two ways   1  for  int k   0  k  lt   data length - 1  k     2  for  int k   0  k  lt  data length  k    and then it will work fine    and to swap you can use  to keep one of the int s in another place and then to replace  int x   data k  data k    data data length - 1  data data length - 1    x    because you don t want to lose one of the int s

User · Answer

Try this       int lowIndex   0      int highIndex   elements length-1       while lowIndex  lt  highIndex            T lowVal   elements lowIndex           T highVal   elements highIndex           elements lowIndex    highVal          elements highIndex    lowVal           lowIndex    1          highIndex - 1

User · Answer

Nope  You could have a function to make it more concise each place you use it  but in the end  the work done would be the same  plus the overhead of the function call  until unless HotSpot moved it inline nbsp  mdash  to help it with that  make the functon static final

User · Answer

inplace swapping  incase you already didn t know  can save a bit of space by not creating a temp variable  arr i    arr i    arr j   arr j    arr i  - arr j   arr i    arr i  - arr j

User · Answer

Solution for object and primitive types   public static final  lt T gt  void swap final T   arr  final int i  final int j        T tmp   arr i       arr i    arr j       arr j    tmp    public static final void swap final boolean   arr  final int i  final int j        boolean tmp   arr i       arr i    arr j       arr j    tmp    public static final void swap final byte   arr  final int i  final int j        byte tmp   arr i       arr i    arr j       arr j    tmp    public static final void swap final short   arr  final int i  final int j        short tmp   arr i       arr i    arr j       arr j    tmp    public static final void swap final int   arr  final int i  final int j        int tmp   arr i       arr i    arr j       arr j    tmp    public static final void swap final long   arr  final int i  final int j        long tmp   arr i       arr i    arr j       arr j    tmp    public static final void swap final char   arr  final int i  final int j        char tmp   arr i       arr i    arr j       arr j    tmp    public static final void swap final float   arr  final int i  final int j        float tmp   arr i       arr i    arr j       arr j    tmp    public static final void swap final double   arr  final int i  final int j        double tmp   arr i       arr i    arr j       arr j    tmp

User · Answer

If you re swapping numbers and want a concise way to write the code without creating a separate function or using a confusing XOR hack  I find this is much easier to understand and it s also a one liner   public static void swap int   arr  int i  int j        arr i     arr i    arr j   -  arr j    arr i        What I ve seen from some primitive benchmarks is that the performance difference is basically negligible as well   This is one of the standard ways for swapping array elements without using a temporary variable  at least for integers

User · Answer

If you want to swap string  it s already the efficient way to do that   However  if you want to swap integer  you can use XOR to swap two integers more efficiently like this   int a   1  int b   2  a    b  b    a  a    b

User · Answer

public class SwapElements    public static void main String   args         int   arr1   new int 5       int   arr2    10 20 30 40        System out println  arr1 Before Swapping     Arrays toString arr1        System out println  arr2 Before Swapping     Arrays toString arr2         int temp        arr1 3    5      arr1 0    2      arr1 1    3      arr1 2    6      arr1 4    10       temp   arr1      arr1   arr2      arr2   temp      System out println  arr1 after Swapping     Arrays toString arr1        System out println  arr2 after Swapping     Arrays toString arr2

User · Answer

This should make it seamless   public static final  lt T gt  void swap  T   a  int i  int j      T t   a i     a i    a j     a j    t     public static final  lt T gt  void swap  List lt T gt  l  int i  int j      Collections  lt T gt swap l  i  j      private void test       String    a     Hello    Goodbye      swap a  0  1     System out println  a   Arrays toString a      List lt String gt  l   new ArrayList lt String gt  Arrays asList a      swap l  0  1     System out println  l   l

[java] Effective swapping of elements of an array in Java

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