The sixth day of Java Foundation Learning--a two-dimensional array and an object oriented introduction

Document Version	Development Tools	Test Platform	Project Name	Date	author	Notes
V1.0				2016.02.25	Lutianfei	None

two-dimensional arrays Format 1 (dynamic initialization)

• Format: 数据类型[][] 变量名 = new 数据类型[m][n] ;
• mIndicates how many one-dimensional arrays of this two-dimensional array
• nRepresents the number of elements per one-dimensional array

• Example:

  • int[][] arr = new int[3][2];
  • Defines a two-dimensional array, arr
  • This two-dimensional array has 3 one-dimensional arrays, the name is arr[0],arr[1],arr[2]
  • Each one-dimensional array has 2 elements, which can be obtained by arr[m][n]

• Note the following format can also represent a two-bit array (deprecated)

  • 数据类型 数组名[][] = new 数据类型][m][n];

Class array2demo{ Public Static void Main(string[] args) {int[] arr =New int[3][2];        System.out.println (arr); System.out.println (arr[0]);the 1th one-dimensional array name of the//arr.System.out.println (arr[1]);the 2nd one-dimensional array name of the//arr.System.out.println (arr[2]);the 3rd one-dimensional array name of the//arr.System.out.println (arr[0][0]); System.out.println (arr[0][1]); }}

Format 2 (dynamic initialization)

• Format:数据类型[][] 变量名 = new 数据类型[m][];
• mIndicates how many one-dimensional arrays of this two-dimensional array
• This time the number of elements of a one-dimensional array is not given directly, and can be given dynamically.
• Example:
  
  • int[][] arr = new int[3][];
  • Arr[0] = new INT[2];
  • ARR[1] = new Int[3]
  • ARR[2] = new INT[1];

Format 3 (static initialization)

• Format:数据类型[][] 变量名 = new 数据类型[][]{{元素…},{元素…},{元素…}};
• Simplified version format:
  
  • 数据类型[][] 变量名 = {{元素…},{元素…},{元素…}};
  • Example:
  • Int[][] arr = {{1,2,3},{4,6},{6}};

two-dimensional array exercises

• Two-dimensional array traversal

//for Loop ImplementationClass array2test{ Public Static void Main(string[] args) {int[] Arr ={{1,2,3},{4,5,6},{7,8,9}}; for(intx=0; x<arr.length;x++) { for(inty=0; y<arr[x].length;y++) {System.out.print (arr[x][y]+"\ T");        } System.out.println (); }    }}//Function ImplementationClass array2test{ Public Static void Main(string[] args) {int[] Arr ={{1,2,3},{4,5,6},{7,8,9}};    PrintArray2 (arr); } Public Static void PrintArray2(int[] arr) { for(intx=0; x<arr.length;x++) { for(inty=0; y<arr[x].length;y++) {System.out.print (arr[x][y]+"\ T");        } System.out.println (); }    }    }

• two-dimensional array summation
  
  • The data of a company by quarter and month are as follows: unit (million yuan)
    
    • First quarter: 22,66,44
    • Second quarter: 77,33,88
    • Third quarter: 25,45,65
    • Quarter Four: 11,66,99

Class array2test{ Public Static void Main(string[] args) {int[] arr = {{ A, the, -},{ the, -, the},{ -, $, $},{ One, the, About}}; System.out.println (SUM (arr) +"Million"); } Public Static int sum(int[] arr) {intsum =0; for(intx=0; x<arr.length;x++) { for(inty=0; y<arr[x].length;y++) {sum + = Arr[x][y]; }        }returnSum }}

• Print Yang Hui triangles (number of lines can be keyboard input)
  

  1: Yang Hui triangle
  
  1
  1 1
  1 2 1
  1 3 3 1
  1 4 6) 4 1
  1 5 10 10 5 1

Analysis:
A: If it is n rows, then the last row is n columns.
B: The first column and the last column of each row are 1 elements.
C: Law:
* The second column of each row begins with the data: the previous column of the previous row + the same column on the previous row

D: The two-dimensional array is composed and then traversed.
When traversing, be careful to imitate the traversal of the 99 multiplication table. Otherwise there will be a lot of 0.

ImportJava.util.scanner;class array2test{ Public Static void Main(string[] args) {Scanner SC =NewScanner (system.in);intn = sc.nextint ();int[] arr =New intN [n]; for(intx=0; x<arr.length;x++) {arr[x][0] =1; ARR[X][X] =1; } for(intx=2; x<arr.length;x++) { for(inty=1; y<=x-1; y++) {Arr[x][y] = arr[x-1][y-1]+arr[x-1][y]; }        } for(intx=0; x<arr.length;x++) { for(inty=0; y<=x;y++) {System.out.print (arr[x][y]+"\ T");        } System.out.println (); }    }}

• Study questions: 1: Parameter transfer problem
  
  • Numerical pass-through problems in Java
    
    • 基本类型: The change of formal parameters has no effect on the actual parameters. ( parameter values are passed)
    • 引用类型: The change of formal parameters directly affects the actual parameters. (The address value is passed)

 Public Static void Main(string[] args) {intA =Ten;intb = -; System.out.println ("A:"+a+", B:"+B);    Change (A, b); System.out.println ("A:"+a+", B:"+B);int[] arr = {1,2,3,4,5};    Change (arr); System.out.println (arr[1]);} Public Static void  Change(intAintb) {System.out.println ("A:"-am", B:"+B);    A = b;    b = A + B; System.out.println ("A:"-am", B:"+B);} Public Static void  Change(int[] arr) { for(intx=0; x<arr.length; X + +) {if(arr[x]%2==0) {arr[x]*=2; }    }}

• Study Questions 2
  
  • A company uses a public telephone to pass data information, which is an integer less than 8 bits, in order to ensure security, encryption is required during delivery, and the encryption rules are as follows:
    
    • First, the data is reversed, then each digit is added 5, and then divided by the remainder of 10 to replace the number,
    • Finally, the first and last digits are exchanged. Please arbitrarily give an integer less than 8 bits,
    • Then, the encrypted results are printed out in the console.

ImportJava.util.scanner;class jiamidemo{ Public Static void Main(string[] args) {Scanner SC =NewScanner (system.in); System.out.println ("Please input a number:");intNumber = Sc.nextint ();        String result = Jiami (number); System.out.println ("Jia mi result is:"+result); } Public StaticStringJiami(intNumber) {int[] arr =New int[8];intindex =0; while(number>0) {Arr[index] = number%Ten;            index++; Number/=Ten; } for(intx=0; x<index;x++) {arr[x] + =5; ARR[X]%=Ten; }inttemp = arr[0]; arr[0] = arr[index-1]; arr[index-1] = temp; String s=""; for(intx=0; x<index;x++) {s+=arr[x]; }returnS }}

[========]

The fourth chapter object-oriented

• This chapter highlights
  
  • Object Oriented thinking
  • Classes and objects and their use
  • Memory diagram of the object
  • The difference between a member variable and a local variable
  • Anonymous objects
  • Package (private)
  • this keyword
  • Construction method
  • Static keyword

Object Oriented thinking

• Eat:

  • process-oriented: Go to the supermarket to buy vegetables------------------------ Cuisine), Cook (dish), waiter (end dish), eat

• Analysis of the elephant in the refrigerator? (How do you analyze which classes are available?) UML, noun extraction method.

  • A: What are the classes?
    
    • Elephant
    • refrigerator
    • Demo
  • B: What are the things in each class?
    
    • Elephant:
      
      • go in
    • refrigerator:
      
      • Open the Door /li>
      • Close
    • Demo:
      
      • Main method
    /li>
  • C: What is the relationship between classes and classes? The functions of the elephant and refrigerator classes are used in the
    
    • demo.

• Code embodiment:

class Elephant {public  Span class= "Hljs-keyword" >static  void  in  () {System.out.println ( "loaded into elephant" );}} Class Refrigerator {public  static  void  open  () {System.out.println (); public  static  void  close  () {System.out.println ( "close the refrigerator Door" );}} Class Demo {public  static  void  main  (string[] args) {Refrigerator Call Open door elephant call go into refrigerator call Close }}

how to be more consistent with object-oriented thinking

• A: First analyze which classes
• B: Then analyze what each class should have
• C: The final analysis of the relationship between classes and classes

Object-oriented development, design, features

• Object 开发 oriented
  
  • is to constantly create objects, use objects, and command objects to do things.
• Object 设计 oriented
  
  • is to manage and maintain the relationship between objects.

• Object oriented特征

  • 封装(encapsulation)
  • 继承(inheritance)
  • 多态(polymorphism)

• How to express a real world thing?

  • 属性Is the descriptive message of the thing.
  • 行为Is what this thing can do

class

• 类: is a set of related properties and behaviors , and is an abstract concept.

• 对象: Is the specific manifestation of such things, the specific existence of the individual .

• Defining a class is actually a member of the 成员变量 definition 成员方法 class (and)

• The same is true in Java for describing things in class.

  • 成员变量is the property of things.
  • 成员方法is the act of Things.

• How to use

  • To create an object:
    
    • 类名 对象名 = new 类名();
  • 对象名.成员变量
  • 对象名.成员方法

memory diagram of an object

• Basic initialization procedure for an object

Class phone{//BrandString brand;//Price    intPrice//ColorString color;//How to call     Public void Pager(String name) {System.out.println ("Call"+name); } Public void SendMessage() {System.out.println ("Send Message!!!"); } Public void PlayGame() {System.out.println ("Play Game!!!"); }}class phonedemo{ Public Static void Main(string[] args) {Phone p =NewPhone (); P.brand ="Nokia"; P.price = -; P.color ="Yellow"; P.call ("chenlixiang~~");        P.sendmessage ();        P.playgame (); System.out.println (P.brand +"---"+p.price+"---"+p.color); }}

memory diagram of two objects

• Note: The method has a common problem with memory addresses in the method area.
  

memory diagram of three objects

• Note: Two references point to the same object
  

The sixth day of Java Foundation Learning--a two-dimensional array and an object oriented introduction