Definition of one-dimensional array and two-dimensional array in JAVA __java

In Java, an array is considered an object

When you define an array, there are two definitions: int[] A and int a[]; the second is a C + + array-defined method, with the first definition of Java recommendations.

The general principle: any object must be initialized before being called.

definition of 11-D arrays

Defines a one-dimensional array that contains three elements

//Method 1, first the new object, and then initialize each element

Int[] A = new int[3];

A[0] = 1;

A[1] = 2;

A[2] = 3;

Method One should note that it cannot be written like this:

Int[] A = new int[3];

A = {1,2,3};

The reason is to create the object in this way with new int[3, the object has been initialized and assigned an initial value of 0, which can be validated with the following code:

Int[] D = new int[3];

for (int i=0;i<d.length;i++) {

System.out.println (D[i]);

}

Enter the result: 0 0 0

If you use a = {1,2,3}; To assign a value, you know that constants cannot be assigned and cannot be modified.

//Method 2, directly assign the initial value to create the object

Int[] B = {1,2,3};

//Method 3,new object to initialize directly

Int[] c = new int[]{1,2,3};

Method Three to note is not to write: int[] c = new int[3]{1,2,3};

This means that the dimension cannot be specified because the dimension expression cannot be defined if an array initialization operation is specified.

Note: If you define an array with new, you must specify its dimensions, so the definition is wrong: int[] D = new int[];

If you cannot determine the number of its elements, you can define this: int[] e = {};

definition of 22-D arrays

is basically similar to a one-dimensional array

Defines a two-dimensional array of 3 rows and 5 columns

//Method 1, first the new object, and then initialize each element

Int[][] A = new int[3][5];

A[0][0]=1;

a[0][1]=2;

a[0][2]=3;

//Method 2, directly assign the initial value to create the object

Int[][] B = {1,1,1,1,1}, {2,2,2,2,2}, {3,3,3,3,3}};

//Method 3,new object to initialize directly

Int[][] A = new int[][] {{1,1,1,1,1}, {2,2,2,2,2}, {3,3,3,3,3}};

Defining a two-dimensional array must specify its number of rows, the number of columns can be specified, and may not be specified.

This definition is correct: int[][] D = new int[3][];

This definition is wrong: int[][] D = new int[][4]; Int[][] D = new int[][];

You can also define an irregular array:

arr = new int[2][];

Arr[0] = new INT[3];

ARR[1] = new INT[5];

3 Length of the array

Length is an attribute of an array (not a Method!), for one-dimensional arrays int[] b = {1,2,3}; The value of B.length is 3,

For two-dimensional arrays, first look at its configuration details: int[][] arr = new INT[2][3];

In this program fragment, a two-dimensional array object with 2 rows and 3 columns is configured, because the data type is int, so the preset element of the array element is 0.

In fact Arr[0], arr[1] are two one-dimensional array objects, each with a length of 3, and the ARR type is int[] [], and the content value is arr[0] and arr[1]. The relationship is shown in Figure 1.

Figure 12-dimensional array configuration relationship

As you can see in Figure 1, arr references int[] [] types of objects, which include arr[0] and arr[1], and arr[0] and arr[1 respectively refer to a one-dimensional array object.

Therefore, the length meaning of arr.length and arr[0].length is different, arr.length represents the number of rows in the array, and Arr[i].length represents the number of elements that the specified row contains. In this case, arr.length=2,arr[0].length=3.

4 The initial value of the array

0L

| td>

Data type	Start   start   value	Data type	Start   start   value
Byte	p>0	Float	0.0f
Short	0	Double	0.0d
int	0	Char	/u0000
Long	Boolean	False