[Classes and Objects, Encapsulation, Construction Method]

Overview of Object-Oriented Thought

1. Process-oriented and object-oriented

• Process Oriented: Emphasizing Process (emphasizing every step of doing something)
• Object-Oriented: Do one thing, not do it yourself, but use objects to accomplish it.

Give an example

• Procedure-oriented: Take a basin, put clothes, put laundry powder, pour water, bubble, rub, rinse, wring dry, and air it.

• Object-Oriented: Put clothes in the washing machine, put laundry powder, press the switch, and air them.

  Call my girlfriend to wash it for me

II. Categories and Objects

1. What are classes and objects?

• Class: A set of attributes and behaviors of a class of things.
• Object: The concrete embodiment of this kind of thing.

2. How to define classes

• Class: A class defined in Java using class.
  • Attribute (member variable): The format of definition is the same as that of previous variables, except that the location has changed, outside the methods in the class.
  • Behavior (member method): Definition format is basically the same as before, except static is removed.

public class Person {


    // Extra-method in class
    // Full name
    String name;

    // Age
    int age;

    // Method
    // Having dinner
    public void eat() {
        System.out.println("People want to eat");
    }

    // Sleep
    public void sleep() {
        System.out.println("People want to sleep");
    }

}

3. How to create and use objects

(1) Creating objects

// Class name object name = new class name ();
// A Person object was created with the object name p
Person p = new Person();

(2) Use objects

// Use attributes: object names. attribute names
p.name;
// Use behavior: object name. method name ()

/**
 * Test class
 */
public class PersonTest {
    public static void main(String[] args) {
        // Write code to simulate various scenarios.
        // To test whether the content in the functional class is correct

        // A Person object was created with the object name p
        Person p = new Person();

        // Object name. Attribute name
        p.name = "Yang Chao";
        p.age = 20;

        // Printing
        System.out.println("The name is: " + p.name + ", Age is: " + p.age);

        p.eat();
        p.sleep(8);



    }
}

4. Membership variables and local variables

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Differences between member variables and local variables

3. Create an object's memory map

IV. Packaging [Key Points]

1. Principles and formats of encapsulation

private: Can modify member variables and member methods, role: privately modified content, can only be accessed in this class.

• Hidden attributes: Decorate attributes with private
• Providing public access to the outside world: get/set method

2. Optimize 1- this

• In the set method, member variables and local variables have the same name.

  • At this point, to follow the principle of proximity, there appears an assignment statement, which becomes: local variables are assigned to local variables.

  age = age; name = name;

this: What problems can be solved?

• When the member variable and the local variable have the same name, the member variable is obtained by using this. variable name.

3. Optimizing 2-Construction Method

• Objective: To assign values to member variables while creating objects.

Construction method

• Format:

Modifier construction method name (parameter list) {}

- No return value type, not even void
 - The name and class name of the constructor are the same

// Spatial-parametric structure/parametric-free structure
 public class name (){

}

// parametric structure/full parametric structure/full parametric structure
 The public class name (parameter list) {// has parameters in parentheses, and the parameters are written according to all member variables in the class.
	this. Property name = the name of a local variable in the parameter list;
}

Effect

1. Used to create objects (when creating objects, the constructor must be called)
2. Initialization (assignment) of members in a class

case

Student category

package com.demo.practice.homework6;

public class Student {
//    Student
//    Attributes: chinese, math, english
//    Behavior: getSum()
        private int chinese;
        private int math;
        private int english;
        public Student(){

        }
        public Student(int chinese,int math,int english){
            this.chinese = chinese;
            this.math = math;
            this.english = english;
        }
        public void setChinese(int chinese){
            this.chinese = chinese;
        }
        public void setMath(int math){
            this.math = math;
        }
        public void setEnglish(int english){
            this.english = english;
        }
        public int getChinese(){
            return chinese;
        }
        public int getMath(){
            return math;
        }
        public int getEnglish(){
            return english;
        }
        public int getSum(){
            return chinese+math+english;
        }

}

Test class

package com.demo.practice.homework6;

public class Test {
    public static void main(String[] args) {
    Student s = new Student(70,60,90);
        System.out.println("chinese:"+s.getChinese()+" math:"+s.getMath()+" english:"+s.getEnglish());
        System.out.println("Total score:"+s.getSum());
    }

}

Summary of Overall Knowledge Points

ps: !!!
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