Learning Note--java Array

1. Creating a one-dimensional array

The simplest and quickest way to do this is to allocate memory to the array at the same time as the declaration. Such as:

  int Month[]=new int[12]

You can also declare and redistribute memory first. Such as:

  int month[];   or int[] month;  Month=new int[12];  

There are two methods that can be used when initializing a one-dimensional array. Such as:

  int arr[]=new int[]{1,2,3,4,5};  Or: int arr[]={1,2,3,4,5};

2. Creating a two-dimensional array

There are two ways to create a two-dimensional array in the same way as a one-dimensional array. Such as:

  First declare the redistribution   int arr[][];   Arr=new int[2][4];  Direct Assignment   int arr[][]=new int[2][4];

Note: Allocating memory can be assigned as a per-dimension assignment, and is commonly used in irregular arrays. Such as:

   int a[][];   A=new int[2][];   A[0]=new int[4];   A[1]=new Int[5];

For the operation of a two-dimensional array, learn to use a foreach statement to traverse a two-dimensional array.

   int arr[][]={{2,3},{3,7},{6,5}};   for (int x[]:arr) {for       (int e:x) {          system.out.print (e+ ");}   }

3. Array manipulation

3.1 Filling elements

After importing Java.util.Arrays, use the Fill () method. Such as:

      Arrays.fill (arr,8);
Arrays.fill (arr,1,2,8);  Padding between first and second (not included) elements 8

3.2 Sort

After importing Java.util.Arrays, use the Arrays.sort () method. Such as:

      int arr[]={2,5,1,7,6};      Arrays.sort (arr);

3.3 Copying an array

Two ways to use the Arrays class:

CopyOf (): Copies the array to the specified length array. Such as:

int arr[]={21,45,46};  int newarr[]=arrays.copyof (arr,5);   The newarr array is: 21,45,46,0,0

Copyofrange (): Copies the specified length array elements to the new array. Such as:

int arr[]={1,4,5,7,8,9}; int Newarr[]=arrays.copyofrange (arr,0,3);

3.4 Array Query

The BinarySearch () method of the Arrays class provides multiple overloads that can be searched using a binary lookup method. Such as:

BinarySearch (Object[],key), BinarySearch (object[],int fromindex,int toindex,int key).

3.5 Array Sorting algorithm

Master the Java program writing of the basic sorting algorithm such as bubble sort, direct selection sorting and so on. Let's take a bubble sort example and write the algorithm yourself in Java:

public class bubblesort{public    void Main (string[] args) {        int arr[]={2,4,8,5,6,10,1};       Create an instance of Bubblesort, call the method sort order        Bubblesort sorter=new bubblesort ();        Sorter.sort (arr);   public void sort (Int. array[]) {for        (int. i=0;i<array.length (); i++) {for           (int j=array.length () -2;j>i;j--)　　{                if (Array[j+1]<array[j]) {                    int temp=array[j+1];                    ARRAY[J+1]=ARRAY[J];                    array[j]=temp;                }             }       }　　}                   

　　

　　　　

Learning Note--java Array