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Day_ 04

2022-06-25 16:25:00 【grp_ grp_ grp】

day_04 Array

1. Array

An array is a reference type , Used to store multiple data

1.1 data structure

Data structure is computer storage 、 How to organize data . Data structure refers to the collection of data elements that have one or more specific relationships with each other . Usually , Well chosen data structure can bring higher operation or storage efficiency . Data structures are often related to efficient retrieval algorithms and indexing techniques

Data manipulation : Additions and deletions

1.2 Array properties

Array properties :

Continuous storage in memory , And subscript from 0 Start ( Memory address offset )

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

therefore Array query and change Efficiency is very high , however Adding and deleting are inefficient

Arrays have a built-in property length Saved the length of the array

stay java in There is one java.util.Arrays class Provides some array operations

1.3 Array declaration

Array declaration

1 Static declaration : When each element is known , 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 = {1,2,3,6,1,2,3};

int[][] arr = {

{1,2,3},{2,1,3},{4,6}

};

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 , For example, in the above program Will save 5 individual 0

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

1.4 storage

1.5 Using an array

1.5.1 get data

1.5.2 Change data

1.5.3 Traverse

1.5.4 Common anomalies

The subscript crossing the line

Null pointer

1.5.5 Array passing

1.6 Value and address

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;