Discussion on some problems of array

1、 Array

Reference data type

Definition ： Used to store multiple data

1.1 data structure

Definition ： data structure It's computer storage 、 How to organize data . data structure A collection of data elements that have one or more specific relationships with each other . Usually , Carefully chosen data structure It can bring higher operation or storage efficiency . data structure It is often related to efficient retrieval algorithms and indexing techniques .

operation ： Additions and deletions

1.2 Array properties

Continuous storage in memory , And subscript from 0 Start

Once the array length is determined The length cannot be changed This means that arrays cannot be added or deleted

Unless you create a new array , Copy the original data into the new array , In the process of copying, you can add and delete

So the query and change of array It's very efficient But the efficiency of adding and deleting is very low

Array has a built-in property length Saved the length of the array

stay Java There is one of them. java.util.arrays class Provides some data operations

1.3  Array declaration

1 Static declaration ： When you know what each element is , Use static declarations

—— data type Variable name = value ;

——int i =2;

data type [] Variable name ={ value , value , value }; Shorthand way

data type [] Variable name =new data type []{ value , value , value }; For example, assign a value to an array twice , You need to write

——int [] arr={1,1,1,122,0};

——int [][] arr={

               {1,1,2} {2,5,6}       };

2 Dynamic statement ： When you don't know every element in the array , Use dynamic declarations

data type [] Variable name =new data type [ length ];

int[] arr=new int [5];

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

Dynamic statement , The default value of the corresponding type is saved, such as in the following program   Five will be saved 0

Integers   0  decimal 0.0,  Boolean   false, character \u0000, Reference type null  

for example

 

1.4 storage

 

 

1.5 Using an array

1.4.1 get data

 

1.5.2 Change data

 

1.5.3 Traverse

 

1.5.4 Common abnormal

1、 Null pointer

 

 

2、 The subscript crossing the line

 

 

1.5.5 Array passing

 

1.5.6Main Method dissemination

 

 

1.6  Value and address

1、 Pass value   It refers to passing values of basic types , Mutual indifference , Because it points to different spaces

 2、 Byref / The reference It refers to passing the value of reference type , Influence each other , It refers to the same heap of memory object space

 

1.7  Array copy

 

public static void main(String[] args) {

                  int[] src = { 2, 3, 4, 5, 6, 7, 8 };

                  int[] dest = { 11, 12, 13, 14, 15, 16, 17, 18 };

                  // int[] dest = { 11, 12, 13, 14,4, 5, 6, 15, 16, 17, 18 };

                  int[] result = copy(src, 2, dest, 3, 3);

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

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

                  }

         }

         /**

          * Insert replication

          *

          * @param src

          *            Source array

          * @param srcPos

          *            Source array start position

          * @param dest

          *            Target array

          * @param destPos

          *            Starting position of target array

          * @param length

          *            Insert number

          * @return

          */

         public static int[] copy(int[] src, int srcPos, int[] dest, int destPos,

                          int length) {

                  // Because it's insert copy , So the length of the array will certainly be changed , Because the array length cannot be changed , So we can only create new arrays , And return the array through the return value

                  /**

                   * 0 Create a new array , The length is dest.length + length

                   *

                   * 1 In the target array from 0 Start To Start position end ( contain ), Copy to a new array

                   *

                   * 2 In source array Starting from the starting position ( contain ) Copy length individual To In the new array

                   *

                   * 3 In the target array From the starting position +1 Start ( contain ) In the end All data Copy to a new array

                   */

                  // 0 Create a new array , The length is dest.length + length

                  int[] newDest = new int[dest.length + length];

                  // 1 In the target array from 0 Start To Start position end ( contain ), Copy to a new array

                  for (int i = 0; i <= destPos; i++) {

                          newDest[i] = dest[i];

                  }

                  // 2 In source array Starting from the starting position ( contain ) Copy length individual To In the new array

                  // Now you need to use the starting position of the target array and change , however The starting position of the target array is also used later , So we can't change

                  // therefore Here, the starting position of the target array Assign to a new variable index, You can change index

                  int index = destPos;

                  for (int i = srcPos; i < srcPos + length; i++) {

                          index++;

                          newDest[index] = src[i];

                  }

                  // 3 In the target array From the starting position +1 Start ( contain ) In the end All data Copy to a new array

                  for (int i = destPos + 1; i < dest.length; i++) {

                          index++;

                          newDest[index] = dest[i];

                  }

                  return newDest;

         }

2. Two dimensional array

2.1 Declaration method

2.2 storage  

 

 2.3  Usage mode

2.3.1  get data

2.3.2  Change data

 

2.3.3  Traverse

 

2.3.4  Dynamic declaration zigzag

 

 3.  The value of the variable

int x = 10;

                  int y = 11;

                  // 1 Intermediate variable ( Development commonly used )

                  int temp = x;

                  x = y;

                  y = temp;

                  System.out.println("x=" + x + ",y=" + y);

                  // 2 Displacement calculation ( For interview )

                  x = 2; // 0000 0010

                  y = 3; // 0000 0011

                  // Convert to the corresponding binary , Every XOR , Take the same 0, Different take 1

                  x = x ^ y; // 0000 0001

                  y = x ^ y; // 0000 0010

                  x = x ^ y; // 0000 0011

                  System.out.println("x=" + x + ",y=" + y);

                  // 3 Addition and subtraction

                  x = 10;

                  y = 20;

                  x = x + y;

                  y = x - y;

                  x = x - y;

                  System.out.println("x=" + x + ",y=" + y);