2018-03-12

An array is a fixed length container that contains data of the same type

1, Declare array:

int[] a; declares an array variable.
[] indicates that the variable is an array
int means that every element in the array is an integer
a is the variable name
However, just this statement will not create an array
Sometimes it is also written as int a []; there is no difference, that is, what kind of pleasant question do you think:

public class HelloWorld {
    public static void main(String[] args) {
        // Declare an array
        int[] a;
    }
}

2, To create an array:

When creating an array, indicate the length of the array. new int[5]
Reference concept:
If the variable represents an array, such as a, we call a reference; different from the basic type: int c = 5; this is called assigning C to 5
Declare a reference int[] a
a = new int[5]; 
Let a point to the array.

public class HelloWorld {
    public static void main(String[] args) {
        //Declare a reference
        int[] a;
        //Create an array with a length of 5 and use the reference a Point to the array
        a = new int[5];
         
        int[] b = new int[5]; //When declared, points to an array
         
    }
}

3, Access array:

public class HelloWorld {
    public static void main(String[] args) {
        int[] a;
        a = new int[5];    
        a[0]= 1;  //Subscript 0, representing the first number in the array
        a[1]= 2;
        a[2]= 3;
        a[3]= 4;
        a[4]= 5;
    }
} 

4, Array length:

The. Length property is used to access the length of an array
Array access subscript range is 0 to length - 1
Once the range is exceeded, an array subscript out of bounds exception will be generated

public class HelloWorld {
    public static void main(String[] args) {
        int[] a;
        a = new int[5];        
        System.out.println(a.length); //Print the length of the array         
        a[4]=100; //Subscript 4, essentially "the fifth", is the last
        a[5]=101; //Subscript 5, essentially "6th", out of range ,Generate array subscript out of bounds exception       
    }
}

5, Initialize array:

1. Space allocation and assignment are carried out step by step:

public class HelloWorld {
    public static void main(String[] args) {
        int[] a = new int[5]; //An array of length 5 was assigned, but no assignment was made       
        //No assignment, then the default value will be used
        //Act as int Array of type, default is 0
        System.out.println(a[0]);    
        //Assignment   
        a[0] = 100;
        a[1] = 101;
        a[2] = 103;
        a[3] = 120;
        a[4] = 140;
    }
}

2. Allocate space and assign:

public class HelloWorld {
    public static void main(String[] args) {
        //Write method 1: assign space at the same time
        int[] a = new int[]{100,102,444,836,3236};
 
        //Style 2: omitted new int[],Same effect
        int[] b = {100,102,444,836,3236};
         
        //Style 3: allocate space and specify content at the same time
        //In this case, the length is 3 and the content is 5, which makes a contradiction
        //So if you specify the contents of the array, you cannot set the length of the array at the same time
        int[] c = new int[3]{100,102,444,836,3236};         
    }
}