// when you want to use less target.setXX(source.getXX), same name
BeanUtils.copyProperties(source, target)

//  most efficient(recommend)
void System.arraycopy(int[] srcArr, int srcBeginPos, int[] resArr, int resBeginPos, int length)
  
int[] Arrays.copyOfRange(int[] array, int start, int end)
  
// to increase array size, idle will be fullfilled with 0
int[] Arrays.copyOf(int[] srcArr, int newArrLength)

int[] ints = {1,2,3};
List<Integer> list = Arrays.stream(ints).boxed().collect(Collectors.toList());

String[] strings = list.stream().toArray(String[]::new);
Array<Integer> list = {0, 1, 2};
int[] array = list.stream().mapToInt(Integer::intValue).toArray()

arr = Arrays.stream(arr).distinct().toArray();

Integer[] cubes = new Integer[] { 8, 27, 64, 125, 256 }; Arrays.sort(cubes, Collections.reverseOrder());

Read more: https://www.java67.com/2016/07/how-to-sort-array-in-descending-order-in-java.html#ixzz8Greh6ggX

Arrays.sort(arr);
int n = arr.length;
int temp;
for(int i = 0; i < n/2; i++) {
    temp = arr[i];
    arr[i] = arr[n - i - 1];
    arr[n - i - 1] = temp;
}

Arrays.stream(arr).max().getAsInt();

Set<Integer> set = new HashSet();
set.add(1);
set.add(2);
List<Integer> list = set.stream().collect(Collectors.toList());
// when specify the type of list use toCollection(ArrayList::new)
set.stream().collect(Collectors.toCollection(ArrayList::new));

Integer.highestOneBit(int n);

n = ~ (1 << k) & n;

for (int submask = mask; submask >= 0; submask = (submask - 1) & mask) {
    // todo something
}

String username = Optional.ofNullable(people).map(People::getName).orElse(null);

// both a and b > 0, faster than
// res = x / y + (x % y != 0 ? 1 : 0);
res = (a + b - 1)/b

// more commonly, use 
(int)Math.ceil((double)a/b);
// or
(int)Math.ceil(a*1.0/y);