"Moving Bricks" Android Primer (4)-Java Development Programming Basics-arrays

05.01_java Language Basics (Array overview and Definition Format description) (learn)

• A: Why do we have arrays (containers)
  
  • To store multiple values of the same data type
• B: Array Concept
  
  • An array is a collection of multiple elements that store the same data type. can also be seen as a container.
  • Arrays can store either the base data type or the reference data type.
• C: Array definition Format data type [] Array name = new data type [length of array];

05.02_java Language Basics (initializing dynamic initialization of arrays) (mastering)

• A: What is the initialization of an array
  
  • is to open up contiguous memory space for arrays and assign values to each array element
• B: How to initialize an array
  
  • A: Dynamic initialization only specifies the length, the system gives the initialization value
    
    • int[] arr = new INT[5];
  • B: Static initialization gives the initialization value, the system determines the length of the
• C: Dynamic initialization format:
  
  • data type [] Array name = new data type [array length];
• D: Case Demo
  
  • Output array names and arrays elements
  
  

05.03_java Language Basics (memory allocations in Java and differences between stacks and heaps)

• A: Stack (Master)
  
  • Store local Variables
• B: Heap (Master)
  
  • Storing new arrays or objects
• C: Method Area
  
  • Object-oriented section explanation
• D: Local Method area
  
  • and system-related
• E: Register
  
  • For CPU use
  
  

05.04_java Language Basics (array of memory plots 11 arrays) (master)

• A: Drawing Demo
  
  • An array
  
  

05.05_java Language Basics (array of memory plots 22 arrays) (Learn)

• A: Drawing Demo
  
  • Two different arrays
  
  

05.06_java Language Basics (array of memory plots 33 references two arrays) (learn)

• A: Drawing Demo
  
  • Three references, two array references to the same address
  
  

05.07_java Language Basics (initializing static initialization of arrays and memory graphs) (master)

• A: The Static initialization format:
  
  • Format: data type [] Array name = new data type []{element 1, element 2,...};
  • Simplified format:
    
    • data type [] Array name = {element 1, element 2,...};
• B: Case Demo
  
  • Explanation of the logarithm group
  • Output array names and arrays elements
• C: Drawing Demo
  
  • An array
  
  

05.08_java Language Basics (two common minor problems with array manipulation out of bounds and null pointers) (master)

• A: Case Demo
  
  • A:arrayindexoutofboundsexception: Array index out-of-bounds exception
    
    • Reason: You have accessed an index that does not exist.
  • B:nullpointerexception: null pointer exception
    
    • Cause: The array is no longer pointing to heap memory. You also use the array name to access the element.
    • Int[] arr = {A-i};
    • arr = null;
    • System.out.println (Arr[0]);
  
  

05.09_java Language Basics (Array operation 1 times calendar) (master)

• A: Case Demo
  
  • Array traversal: Is the output of each element in the array sequentially.
  • Properties of the array: length of the arr.length array
  • Maximum index of the array: arr.length-1;
    1. public static void print (int[] arr) {
    2. for (int i = 0;i < Arr.length; i++) {
    3. System.out.print (Arr[i] + "");
    4. }
    5. }
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05.10_java Language Basics (Array operations 2 get the maximum) (master)

• a: Case demo
  
  • array gets the maximum value ( Gets the maximum minimum value in the array)
    1. public static int Getmax (int[] arr) {
    2.     int max = arr[0];
    3.     for (int i = 1;i < arr.length; i++) {         //from the second element of the array, start traversing the /li>
    4.         if (Max < arr[i]) {           &nb sp;            //If Max records a value less than the element in the array
    5.             max = arr[i];                    &nb sp;      //max record larger
    6.         }
    7.    }
    9.     return max;
    10. }
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05.11_java Language Foundation (operation of Array 3 inversion) (master)

• A: Case Demo
  
  • array element inversion (that is, swapping elements)
    1. public static void Reversearray (int[] arr) {
    2. for (int i = 0;i < ARR.LENGTH/2; i++) {
    3. Arr[0] and arr[arr.length-1-0] Exchange
    4. ARR[1] and Arr[arr.length-1-1] Exchange
    5. ARR[2] and Arr[arr.lentth-1-2]
    6. //...
    8. int temp = Arr[i];
    9. Arr[i] = arr[arr.length-1-i];
    10. Arr[arr.length-1-i] = temp;
    11. }
    12. }
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05.12_java Language Basics (Array operations 4 look-up Table method) (master)

• A: Case Demo
  
  • Array Lookup Table method (according to the keyboard input index, find the corresponding week)
    1. public static char Getweek (int week) {
    2. Char[] arr = {', ' one ', ' two ', ' three ', ' four ', ' V ', ' VI ', ' Day '}; Define a weekly table
    3. return Arr[week]; Get the elements in a table by index
    4. }
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05.13_java Language Basics (array of Operations 5 basic Find) (master)

• A: Case Demo
  
  • Array element Lookup (finds the index of the first occurrence of the specified element in the array)
    1. public static int GetIndex (int[] arr,int value) {
    2. for (int i = 0;i < Arr.length; i++) {//array traversal
    3. if (arr[i] = = value) {//If the elements in the array match the elements found
    4. return i;
    5. }
    6. }
    7. return-1;
    8. }
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05.14_java Language Basics (two-dimensional array overview and Format 1) (Learn)

• A: A Two-dimensional array overview
• B: two-dimensional array format 1
  
  • int[][] arr = new int[3][2];
• C: Interpretation of the two-dimensional array format 1
• D: Precautions
  
  • A: The following format can also represent a two-dimensional array
    
    • 1: Data type array name [] = new data type [m][n];
    • 2: Data type [] array name [] = new data type [m][n];
  • B: Note the differences defined below
  • 1. int x;
    2. int y;
    3. int x, y;
    5. Int[] x;
    6. Int[] y[];
    8. Int[] x,y[]; X is a one-dimensional array, and Y is a two-dimensional array
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• E: Case Demo
  
  • Define two-dimensional arrays, output two-dimensional array names, one-dimensional array names, one element
  
  

05.15_java Language Basics (memory plots for two-dimensional array format 1) (Learn)

• A: Drawing Demo
  
  • Drawing explains the problem of the above two-dimensional array name, one-dimensional array name, and the value of an element
  
  

05.16_java Language Basics (Explanation of two-dimensional array format 2 and its memory plots) (learn)

• A: Two-dimensional array format 2
  
  • int[][] arr = new int[3][];
• B: Interpretation of the two-dimensional array format 2
• C: Case Demo
  
  • Explain formats, output data, and draw memory graphs
  
  

05.17_java Language Basics (Explanation of two-dimensional array format 3 and its memory plots) (learn)

• A: Two-dimensional array format 3
  
  • Int[][] arr = {{1,2,3},{4,5},{6,7,8,9}};
• B: Interpretation of the two-dimensional array format 3
• C: Case Demo
  
  • Explain formats, output data, and draw memory graphs
  
  

05.18_java Language Basics (two-dimensional array Exercise 1-times Calendar) (master)

• A: Case Demo
  
  • Requirements: two-dimensional array traversal
  • The outer loop controls the length of the two-dimensional array, which is actually the number of one-dimensional arrays.
  • The inner loop controls the length of a one-dimensional array.
    1. Int[][] arr = {{1,2,3},{4,5},{6,7,8,9}};
    3. for (int i = 0;i < Arr.length; i++) {//get to one-dimensional array in each two-dimensional array
    4. for (int j = 0;j < Arr[i].length; J + +) {//Gets the elements in each one-dimensional array
    5. System.out.print (Arr[i][j] + "");
    6. }
    8. System.out.println ();
    9. }
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05.19_java Language Basics (two-dimensional array exercises 2 summation) (master)

• A: Case Demo
• 1. Requirements: Sum of annual sales of company
  2. the data for a company by quarter and month are as follows: unit (million)
  3. first quarter: 22,66,44
  4. second quarter: 77,33,88
  5. third quarter: 25,45,65
  6. fourth quarter: 11,66,99
  8. int[][] arr = {{22,66,44},{77,33,88},{25,45,65},{11,66,99}};
  10. int sum = 0;                     &nb Sp              //define variables to record the result of each addition
  11. for (int i = 0;i < arr.length; i+ +) {         //get each one-dimensional array
  12.     for (int j = 0;j < Arr[i].length; J + + ) {   //Gets the elements in each one-dimensional array
  13.         sum = sum + arr[i][j];     ;              //cumulative
  14.    }
  15. }
  17. System.out.println (sum);
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05.20_java Language Basics (Study questions in Java and parametric transfer problems and illustrations) (master)

• A: Case Demo
• 2. Read the program to write the results, and draw the memory diagram to explain
  4. public static void Main (string[] args) {
  6. int a = 10;
  8. int B = 20;
  10. System.out.println ("A:" +a+ ", B:" +b);
  12. Change (A, b);
  14. System.out.println ("A:" +a+ ", B:" +b);
  18. Int[] arr = {1,2,3,4,5};
  20. Change (arr);
  22. System.out.println (arr[1]);
  24. }
  28. public static void Change (int a,int b) {
  30. System.out.println ("A:" +a+ ", B:" +b);
  32. A = b;
  34. b = A + B;
  36. System.out.println ("A:" +a+ ", B:" +b);
  38. }
  42. public static void Change (int[] arr) {
  44. for (int x=0; x<arr.length; x + +) {
  46. if (arr[x]%2==0) {
  48. arr[x]*=2;
  50. }
  52. }
  54. }
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"Moving Bricks" Android Primer (4)-Java Development Programming Basics-arrays