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Arrays and collections
2022-07-06 05:52:00 【Python's path to immortality】
Length() Used to find String The length of the string object ,length Is to seek String Length of array
Array declaration and initialization
String[] a= new int[3] The length of the array is fixed and cannot be modified
String [] a=new String[]{“a”,”b”,”c”} The value of the first element in is a instead of “a”;
Array traversal method :
1for(var i:a ){
system.out.println(i);
}
2For(int i=0;i<a.lenth;i++){
System.out .prontln(i);}
3Arrays.stream(a).foreach(system.out::println)
Assign random numbers to the elements in the array
Random rand=new Random();
Int[] s=new int[10];
S[i]=rand.nextInt(100)+1;
Sort using Arrays.sort The method needs to int[] Convert to Integer object
Descending Arrays.sort(n,(a,b)->b-a)
Arrays.sort(ss, Comparator.reverseOrder())
// Bubbling
for (int i = 0; i < nums.length - 1; i++) {
for (int j = 0; j < nums.length - 1 - i; j++) { //> Ascending < Descending
if (nums[j] < nums[j + 1]) {
int t = nums[j]; nums[j] = nums[j + 1];
nums[j + 1] = t; }
Arrays.fill( Array name , Location )// Fill the array
Sorts// Ascending order
Arrays.binarySearch(n, 150)) Sort before you can find
aggregate Collection
ArrayList yes list Implementation class of
List.of Added list Fixed size list
List.add() Additive elements
List.remove Remove elements ( The element that first appears from the left )
List.clear() Empty the set
List.contains Determine whether there is
// Instantiation ArrayList Use generics var list = new ArrayList(); Traversal is the same as array
//array list transformation
int[] arr = new int[]{1,2,3};
List lis = new ArrayList(Arrays.asList(arr));
System.out.println(lis.get(0)); // take arr Put the whole as a parameter list in
System.out.println(lis.size())
aggregate Arraylist And Array Array type conversion (
// Array to set () To put it bluntly, it is to add an array as a set element )
Integer[] nums = new Integer[] { 10, 20, 30, 40, 50 };
List list = Arrays.asList(nums);
// Set array (list.toArray)
//Arrays.toString Output the array as a string
List Generic sort
List list = new ArrayList<>();
List.sort// Ascending
Collcetions.shuffle(list)// Disorder
Collcetions.sort(list)// Disorder
Collections.sort(ls, Comparator.reverseOrder());// Descending
list.sort((a, b) -> b.getScore() - a.getScore());// According to the ascending order of grades
list.sort(Comparator.comparingInt(User::name));// Sort by name ava.util.Comparator Interface It can realize multi-level sorting
Add two data at the same time
List.add(S)
Set Set :
HashSet :Set The implementation of the interface has good access and search performance At the bottom is the hash table
disorder , Out of sync , The set value can be empty and cannot contain duplicate elements
Traverse set.foreach(system.out::println)
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