5. Object-oriented VS process-oriented in Java

1. Object-oriented VS process-oriented

 1 /* 2  * 理解一：人开门 3  * 面向过程：人 打开门 4  * 面向对象： 5  * 人{ 6  *    打开(){ 7  *        门。开开(); 8  *    } 9  * }10  * 门{11  *     开开(){12  *     }13  * }14  * 
15  * 理解二：人把大象装进冰箱16  * 面向过程：17  *     1、打开冰箱；18  *     2、把大象放进去；19  *     3、关闭冰箱门；20  * 面向对象：21  * 人{22  *     打开(冰箱){冰箱.开开()}23  *     操作(大象){大象。进入(冰箱)}24  *     关闭(冰箱）{冰箱。合上()}25  * }26  * 大象{27  *     进入(冰箱){}28  * }29  * 冰箱{30  *     开开(){}31  *     合上(){}32  * }33  */

2. Object-oriented programming focuses on the design of classes!

　2.1. No matter how large a project or project is, it must be composed of classes one by one.

　2.2. Classes are abstract, like drawings for manufacturing a car. The specific cars are manufactured according to the drawings, which are actually instantiations of the class

 1 /* 2  * 1、面向对象的编程关注于类的设计 3  * 2、设计类实际上就是设计类的成员 4  * 3、基本的类的成员，属性(成员变量或Field)&方法（Method） 5  */ 6 public class TestPerson { 7     public static void main(String[] args) { 8         Person p1 = new Person(); 9         p1.info();10         11         p1.name = "钟超";12         p1.age = 21;13         p1.sex = true;14         p1.info();15         16         p1.setName("张三");//p1.name = "张三"17         p1.info();18         19         Person p2 = p1;20         System.out.println("P1:" + p1);21         System.out.println("P2:" + p2);22         p2.info();23         24         p2 = new Person();25         System.out.println("P2:" + p2);26         p2.info();27         //实例化Scanner类的对象，通过此对象.nextXxx的方法进行调用，完成相应的功能；28         Scanner s = new Scanner(System.in);29         int i = s.nextInt();30         31         Person p3 = new Person();32         p3.info();33     }34 }35 //类：是抽象的。36 class Person{37     //1.属性38     String name;39     int age = 10;40     boolean sex;41     42     //2.方法43     public void eat(){44         System.out.println("人吃饭");45     }46     public void sleep(){47         System.out.println("人睡觉");48     }49     50     public String getName(){51         return name;52     }53     public void setName(String n){54         name = n;55     }56     57     public void info(){58 //        eat();59 //        sleep();60         System.out.println("name:" + name + "age:" + age + "sex:" + sex);61     }62 }

3. The idea of ​​completing a project (or function)

3.1. Whether the object of the class corresponding to the function to be completed exists;

3.2. If it exists, just call the properties or methods in the corresponding class directly through the object;

3.3. If it does not exist, you need to create an object of the class. Even if the class does not exist, you need to design the class;

4. The three main lines of object-oriented programming:

　1. Classes and their components: attributes, methods, constructors, code blocks, internal classes

　2. Characteristics of object-oriented programming: encapsulation, inheritance, polymorphism (abstraction)

　3. Other keywords: this super package import static final abstract interface...

Class:

1. Focus on the design of the class

2. Class components:

1. Attributes (member variables, Field)

　2. Method (member method, function, Method)

3. About attributes:

4. Method:

  1 /*  2  * 一、面向对象思想的落地法则一：  3  * 1.设计类并设计类的成员（成员变量&方法）  4  * 2.通过类来创建类的对象（也称作类的实例化）  5  * 3、通过“对象。属性”或“对象。方法”来调用，完成相应的功能  6  * 
  7  * 二、创建的多个对象，彼此各自拥有一套类的属性，当对其中一个对象的属性进行修改时。  8  * 不会影响到其他对象的属性值。  9  * 
 10  * 三、类的属性(成员变量) 11  *     成员变量    VS     局部变量 12  *     相同点：1、遵循变量声明的格式；数据类型 变量名 = 初始化值； 13  *          2、都有作用域： 14  *     不同点：1、声明的位置的不同：成员变量：生命在类里，方法外边； 15  *                               局部变量：声明在方法内，方法的形参部分，代码块内 16  *          2、成员变量的修饰符有四个：public(公共的) private(私有的) protected 缺省 17  *                    局部变量没有修饰符：与所在的方法的修饰符一样； 18  *          3、初始化值：一定会有初始化值； 19  *                   成员变量：如果在声明的时候，不显示的赋值，那么不同的数据类型会有不同的默认初始化值； 20  *                 byte short int long = 0； 21  *                 float double = 0。0； 22  *                 char = 空格； 23  *                 boolean = false； 24  *                 引用类似的变量  = null； 25  *                  局部变量：一定要显示的赋值（局部变量没有默认初始化值）； 26  *          4、二者在内存中存放的位置不同，成员变量在堆空间中，局部变量在栈空间中； 27  * 总结：关于变量的分类：1、按照数据类型的不同：基本数据类型(8种)&引用数据类型 28  *                  2、按照声明位置的不同：：成员变量&局部变量 29  * 
 30  * 四、类的方法：提供某种功能的实现 31  *         1、实例    public void eat(){方法体} 32  *               public String getName(){} 33  *               public void setName(String n){} 34  *         2、格式：权限修饰符  返回值类型(void：无返回值/具体返回值) 方法名(形参){} 35  *         3、关于返回值类型 void：表名此方法不需要返回值 
 36  *                     有返回值的：在方法的最后一定有return + 返回值类型对应的变量 37  *           记忆：void与return不可以同时出现在一个方法内。 38  *         4、方法内可以调用本类的其他方法和属性，但是不能再方法内在定义其他方法； 39  * 
 40  * ClassRoom Car ... 41  */ 42 public class Zoo { 43     public static void main(String[] args) { 44         //基本数据类型的声明：数据类型 变量名 = 初始化值； 45         int i = 10; 46         //1.类的实例化：如下的a1就是一个实实在在的对象 47         Animal a1 = new Animal(); 48         //int[] arr = new int[10]; 49         //通过对象调用属性 50         a1.name = "花花"; 51         a1.age = 3; 52         System.out.println("name:" + a1.name + "\t" + "age:" + a1.age); 53         //通过对象调用方法 54         a1.eat(); 55         a1.sleep(); 56          57         //在创建一个对象 58         Animal a2 = new Animal(); 59         System.out.println("name:" + a2.name + "\t" + "age:" + a2.age); 60         a2.name = "小花"; 61         System.out.println("name:" + a1.name + "\t" + "age:" + a1.age); 62         System.out.println("name:" + a2.name + "\t" + "age:" + a2.age); 63         //a3与a1一样,a3不意味着相较于a1重新创建的一个对象，而是a1与a3共用一个对象实体 64         Animal a3 = a1; 65         System.out.println("name:" + a3.name + "\t" + "age:" + a3.age); 66         a3.name = "维尼熊"; 67         System.out.println("name:" + a1.name + "\t" + "age:" + a1.age); 68          69         System.out.println(a2.getName()); 70         System.out.println(a2.desc()); 71     } 72 } 73  74 class Animal{ 75     //1.属性 76     String name; 77     int age; 78     //2.方法 79     public void eat(){ 80         System.out.println("动物进食"); 81     } 82     public void sleep(){ 83         System.out.println("动物休眠"); 84         //return; 85     } 86     public String getName(){ 87         return name; 88     } 89     public int getAge(){ 90         return age; 91         //其后不可以声明语句 92         //System.out.println("Hello"); 93     } 94     //当通过对象调用此方法是，会将方法的返回值提供给方法的调用者，也就是当前的对象。 95     public String desc(){ 96         if(age > 2){ 97             return "恰同学少年"; 98         }else{ 99             return "还是看动画片的 年龄";100         }101     }102     public void setName(String n){103         name = n;104     }105     public void addAge(){106         int i = 2;107         age += i;108     }109     public void info(){110         //可以在方法内调用本类的其他方法，但是不可以在方法内在定义新德尔方法111         eat();112         sleep();113 //        public void breathJ(){114 //            System.out.println("呼吸");115 //        }116     }117     //System.out.println("Hello!");118 }

5 , The first rule of implementation of object-oriented programming ideas:

1. Design and create classes and class components;

2. Instantiate class objects;

3. Pass Complete a certain function in the form of "object.property" or "object.method"

6. Class initialization memory analysis:

6.1. Memory division structure:

Stack: local variables, object reference names, array reference names

Heap: "things" coming out of new (for example: object entities, array entities), including member variables

Method area: Contains string constants

Static domain: Variables declared as static

6.2. On the basis of understanding, you must learn how to create basic class objects in memory in operation.

7. Overloading of methods:

Requirements: 1. In the same class;
* 2. The method names must be the same;
* 3. Methods The parameter list is different; 1. The number of parameters is different;
* 2. The parameter types are different;
* 4. The overloading of the method has nothing to do with the return value type of the method;

 1 /* 2  * 方法的重载(overload) 3  * 要求：1、同一个类中； 4  *        2、方法名必须相同； 5  *        3、方法的参数列表不同；1、参数的个数不同； 6  *                       2、参数类型不同； 7  *        4、方法的重载与方法的返回值类型没有关系； 8  */ 9 public class TestOverLoad {10 11 }12 class OverLoad{13     //定义两个int型变量的和14     public int getSum(int i, int j){15         return i + j;16     }17     //定义三个int型变量的和18     public int getSum(int i, int j, int k){19         return i + j + k;20     }21     //不能与其他几个方法构成重载22 //    public int getSum1(int i, int j, int k){23 //        return i + j + k;24 //    }25 //    public void getSum(int i, int j, int k){26 //        System.out.println(i + j + k);27 //    }28     //定义两个double型的数据的和29     public double getSum(double d1, double d2){30         return d1 + d2;31     }32     //定义三个double型数据的和33     public void getSum(double d1,double d2,double d3){34         System.out.println(d1 + d2 + d3);35     }36     //以下两个方法也构成重载37     public void method1(int i, String str){38         39     }40     public void method1(String str1, int j){41         42     }43 }

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