How to define array

Method of array definition: 1. Declare a one-dimensional array [int[] a;]; 2. Initialize and give a value [int[] a={1,2,3,4,5}] ; 3. Declare the two-dimensional array [int[][] a;]; 4. Initialize and give the value [int[][] a={{1,2},{2,3},{3,4} }].

#The operating environment of this article: Windows 7 system, Dell G3 computer.

What is an array:

An array (Array) is an ordered sequence of elements. If a limited collection of variables of the same type is named, then the name is the array name. The individual variables that make up an array are called components of the array, also called elements of the array, and sometimes called subscript variables. The numeric number used to distinguish the individual elements of an array is called a subscript. In programming, an array is a form of organizing several elements of the same type in an orderly manner for the convenience of processing. These ordered collections of similar data elements are called arrays.

Array is a collection used to store multiple data of the same type.

Method of array definition:

1. One-dimensional array

1),

int[] a;

//Declaration, no initialization

2),

int[] a=new int[5];

//Initialized to the default value, int type is 0

3),

int[] a={1,2,3,4,5};

//Initialized to a given value

4),

int[] a=new int[]{1,2,3,4,5};   //同(3)

int[] a=new int[5]{1,2,3,4,5};

Error, if an array initialization operation is provided, the dimension cannot be defined Expression

5),

int[] a;

  a=new int[5];

//Correct, the same as (2)

int[] a;

 a={1,2,3,4,5};

//Error, array constants can only be initialized Use

6),

int a[];

 a[0]=1;

//Error, because the array is not initialized and cannot be assigned

a[1]=2;

2, two-dimensional array

1),

int[][] a;

//Declaration, no initialization

2),

int[][] a=new int[2][3];

//Initialized to the default value, int type is 0

3),

int[][] a={{1,2},{2,3},{3,4}};

//Initialized to the given value

int[][] a={{1,2},{2,3},{3,4,5}};

//Nothing wrong, the array space is not allocated continuously, so the size of each dimension is not required to be the same

4),

int[][] a=new int[2][];

a[0]=new int[3];

//a[0] In fact, it is an array

a[1]=new int[4];

//The size of each dimension can be different;

5),

int[][] a=new int[][]{{1,2},{2,3},{3,4,5}};   //同(3)

 int[] a=new int[5]{{1,2},{2,3},{3,4,5}};

//Error, if provided Without the array initialization operation, the dimension expression cannot be defined

  int[][] a=new int[2][];

a[0]={1,2,3,4,5};

//Error, array constants can only be used in the initialization operation

6),

int[][] a=new int[2][];

 a[0][1]=1;

//Error, the second dimension is not initialized and cannot be assigned, java.lang.NullPointerException exception

Extended knowledge

Array memory is continuous

The array is a whole, and its memory is continuous; that is to say, the array elements are next to each other, and there is no point between them. gap. The following figure demonstrates the storage situation of int a[4]; in memory:

"The array memory is continuous" is very important, so I used a large Title for emphasis. Contiguous memory provides convenience for pointer operations (accessing array elements through pointers) and memory processing (copying, writing, etc. of the entire memory), which allows the array to be used as a cache (a piece of memory that temporarily stores data).

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