how to swap array elements in java code example

Example 1: java array swap

public static void swap(int x, int y, int[] arr) {
  	int temp = arr[x];
  	arr[x] = arr[y];
  	arr[y] = temp;
}

Example 2: array.swap java

public static final <T> void swap (T[] a, int i, int j) {
  T t = a[i];
  a[i] = a[j];
  a[j] = t;
}

public static final <T> void swap (List<T> l, int i, int j) {
  Collections.<T>swap(l, i, j);
}

private void test() {
  String [] a = {"Hello", "Goodbye"};
  swap(a, 0, 1);
  System.out.println("a:"+Arrays.toString(a));
  List<String> l = new ArrayList<String>(Arrays.asList(a));
  swap(l, 0, 1);
  System.out.println("l:"+l);
}

Example 3: swap chunks of array in java

import java.util.Arrays;

// ... //

int[] digits = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };

// Rotate is a fancy way to say split around an index, and swap the chunks
// For the comments, assume `A=digits`
int[] rotate(int[] A, int r) {
  int N = A.length; // total number of elements
  
  // Arrays.copyOfRange(array, start, end) will return array[start:end),
  // where start is inclusive and end exclusive
  int[] left = Arrays.copyOfRange(A, 0, r); // [0,1,...,r-1], so r=3->[0,1,2]
  int[] right = Arrays.copyOfRange(A, r, N); // [r,r+1,...,N-1], so r=7->[7,8,9]
  
  // Now, concatenate right with left and store in result
  // - in JS this would be `result=[...right, ...left]`
  int[] result = new int[N];
  int R = N - r; // length of right array
  for(int i=0; i<N; ++i) {
    // ternary expression: same as
    //   `if(i<R) result[i] = right[i];`
    //   `else    result[i] = left[i-R];`
    result[i] = i<R ? right[i] : left[i-R];
  }
  
  return result;
}

Example 4: array.swap java

String temp = arr[1];
arr[1] = arr[2];
arr[2] = temp;