Array related knowledge

1. The concept of array ：

An array is a memory area used to store a batch of data of the same type （ Can be understood as a container ）, Arrays are suitable for storing a batch of data of the same type

2. Static initialization of arrays ：

Assign values to the array while defining the array variables

Format ：

// Format 1
int[] a = new int[]{
    1,2,3};
// Format 2
int[] a = {
    1,2,3};

principle ：

int[] ages = {
    12,24,36};

Array variable name ages Save the address of array space in heap memory , So array variable names and index numbers can access array elements arr[0]

3. Dynamic initialization of arrays ：

When defining an array, only determine the type of element and the length of the array , Then store the specific data

Format ：

int[] a = new int[10];

principle ：

Default value of element during dynamic initialization ：

What are the differences between the characteristics and scenarios of the two arrays ： The stored element value is already known , Initialize with static . It's not clear what data to store , Initialization with dynamic . The two formats are written independently , Do not mix .

5. Array access

Arrays are reference data types , Each element in the array can be accessed through the array variable name and index number
Access format ： Array variable name [ Reference no. ]
Length of array ： Array variable name .length
Maximum index of array ： The length of the array -1（ The premise is that the number of elements is greater than 0）

6. Traversal of array :

Traversal is to access the elements in the array one by one

Traversal format ：

int[] a = {
    1,2,3};
for(int i =0;i<a.length;i++){
    
	System.out.println(a[i]);
}

7.Java Introduction to memory allocation ：

Two array variables point to the same array ：

8. Array considerations ：

• An array type [] Array name Or you could write it as An array type Array name []
• What type of data does the array store , Otherwise, an error will be reported
• Once the array is defined , Program execution , length , The type is fixed
• If the accessed element position exceeds the maximum index , When it's executed ArrayIndexOutOfBoundsException( Array index out of bounds exception )
• If there is no address to store the array in the array variable , It is null, When accessing array information NullPointerException( Null pointer exception )