Java Array Chapter Summary

Array (array of Yu Shunji and Wang Wei)

1. Array: A container that stores multiple elements of the same data type.

2, Characteristics: Each element has a number, starting from 0, The maximum number is the length-1. Number of professional names: index

3. Define the format

3.1): data type [] array name;

3.2): data type array name [];

Recommendation is a way, B method forget it. But to be able to read

4. Initialization of arrays

4.1) Dynamic Initialization

Give only the length, the system gives the default value

Example: int[] arr = new int[3];

4.2) Static Initialization

Given the value, the system determines the length

Example: int[] arr = new int[]{1,2,3};

Simplified version: int[] arr = {£ º};

5. Memory allocation in Java

Stack store local Variables

Heap store all new out of

Method Area (object-oriented part explained in Detail)

Local Method Area (system-dependent)

Register (CPU Usage)

Memory Graph:

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Attention:

A: A local variable is defined in the method definition or on a method Declaration.

B: The difference between stack memory and heap memory

Stack: when the data is used, it Disappears.

Heap: every new one comes with an address.

Each variable has a default value

Byte,short,int,long 0

float,double 0.0

Char ' \u0000 '

Boolean false

Reference type NULL

After the data is used, it is recycled when the garbage collector is Idle.

6. Array Memory Graph

An array

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Array of two

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C: three arrays (two stack variables point to the same heap Memory)

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7. Array Traversal case:

7.1) Traversal:

mode 1:public static void PrintArray (int[] arr) {for (int x=0; x<arr.length; x + +) {System.out.println (arr[x]);}} Way 2:public static void PrintArray (int[] Arr) {System.out.print ("["); for (int x=0; x<arr.length; x + +) {if (× = = Arr.length-1) {System.out.println (arr[x]+ "]");} else {System.out.println (arr[x]+ ",");}}}

7.2) Maximum Value

Maximum value: publicstatic int getmax (int[] arr) {int max = arr[0];for (int x=1; x<arr.length; x + +) {if (arr[x] > max) {max = arr[x];}} Return max;}  min: public static int getmin (int[] arr) {int min = arr[0];for (int x=1; x<arr.length; x + +) {if (arr[x] < Min) {min = arr[x];}} Return min;}

7.3) reverse Order

mode 1:public static void reverse (int[] arr) {for (int x=0; x<arr.length/2; x + +) {int temp = arr[x];arr[x] = Arr[arr.leng th-1-x];arr[arr.length-1-x] = temp;}} mode 2:public static void reverse (int[] arr) {for (int start=0,end=arr.length-1; start<=end; start++,end--) {int temp = a rr[start];arr[start] = arr[end];arr[end] = temp;}}

7.4) Basic Search

Way 1:public static int getindex (int[] arr,int value) {for (int x=0; x<arr.length; x + +) {if (arr[x] = = Value) {return x;} }return-1;} mode 2:public static int getindex (int[] arr,int value) {int index = -1;for (int x=0; x<arr.length; x + +) {if (arr[x] = = Val Ue) {index = x;break;}} Return index;}

7.5) Check Table:

public static String getString (string[] strarray,int Index) {return strarray[index];}

7.6) Keyboard Entry score Array case:

Import java.util.scanner;class TestArr1 {public static void main (string[] Args) {Scanner s = new Scanner (system.in);d ouble [] scores = new Double[5];d ouble sum = 0;double avg = 0;double min = 100;double max = 0;for (int i = 0;i<scores.length; I++) {scores[i]=s.nextdouble ();} for (int i = 0;i<scores.length;i++) {sum + = scores[i];if (scores[i]<min) {min = scores[i];} If (scores[i]>max) {max = scores[i];}} AVG = sum/scores.length; System.out.println ("average score:" +avg+ ", lowest score:" +min+ ", highest score:" +max);}}

Two-dimensional arrays

2.1) the element is an array of one-dimensional arrays.

2.2) format:

A: data type [] array name = new data type [m][n];

B: data type [] array name = new data type [m][];

C: data type [] array name = new data type [][]{{...},{...},{...}};

D: data type [] array name = {{...},{...},{}};

2.3) Traversal case

Import java.util.scanner;class testarr {public static void main (String[]  Args)  {/*int[][] arr = {{1,2,3},{2,3,4},{3,4,5}};int[][] _arr = {};int[][]  arr1 = new int[3][2]; int[][] _arr1 = new int[][]{{1,2,3},{2,3,4 },{3,4,5}};int [][] arr2 = new int[3][];arr2[0] = new int[]{1,2,3}; Arr2[1] = new int[]{2,3,4};arr2[2] = new int[]{5,6,7};//int[][][] arr3  = new int[5][6][6];//traversal of a two-dimensional array  //a layer of loops is the traversal of all one-dimensional arrays in the two-dimensional for (int i = 0;i< Arr2.length;i++) {//two layers Loop through all elements in a one-dimensional array for (int j = 0;j<arr2[i].length;j++) {System.out.print (ARR2 I [j]+ "\ t");} System.out.println ();} *///defines a two-dimensional array of length 3 with 3 one-dimensional arrays of length 3//adds numbers to It,//1 2 3//4 5 6//7 8 9scanner s  = new scanner (system.in); int n = s.nextint (); int[][] arr =&nBsp;new int[n][n];int number = 1;for (int i = 0;i<arr.length;i++) {for (int  j = 0;j<arr[i].length;j++) {arr[i][j] = number; number++;}} For (int i = 0;i<arr.length;i++) {for (int j = 0;j<arr[i].length;j++) { System.out.print (arr[i][j]+ "\ t");} System.out.println ();}}}

2.4) Index Case:

Class Test24_2 {public static void main (string[] Args) {int [] arr = new Int[]{2,3,4,45,66,7,4};int MaxNumber = INTEGER.MI N_value;int Minnumber = Integer.max_value;int Maxindex = 0;int Minindex = 0;for (int i = 0;i<arr.length;i++) {if (ARR[I]&G T;maxnumber) {maxnumber = Arr[i];maxindex = i;} If (arr[i]<minnumber) {minnumber = Arr[i];minindex = i;}} System.out.println ("max:" +maxnumber+ "index is:" +maxindex+ ", min:" +minnumber ");}}

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Java Array Chapter Summary