Object-oriented knowledge essentials

package Demo01;
/**
 * Object-oriented:
 * Procedure-oriented and object-oriented:
 * Process-oriented: Process-oriented is to analyze the steps required to solve the problem, and follow these steps to realize step by step
 * Object-oriented: Object-oriented is to decompose the things that make up the program into various objects (find participants), and the purpose of creating objects is not to complete a step,
 * but to describe how something behaves throughout the problem-solving steps
 * 			
 * Object: An entity that describes objective things, consisting of a set of properties and methods
 * class: an abstraction of an object (extracted part of the image) class    
 * First there are specific objects, then abstract the like between each object, and summarize the categories to recognize other objects through categories
 * 		
 * Attributes in the object: -- "The specific characteristics of the object (basic information) noun
 * Each property of each object has a specific value;
 * For example: The name, age, weight...
 * Defined in the class, called member variables/class variables/member properties, which act on the entire class body
 * Format:
 * [modifier] attribute type attribute name = [default]; optional
 *     						[public]     String     name  =  [null] ；
 *     
 * Method in the object: --> The operation (behavior) performed by the object Verb
 * Definition format:
 * [modifier] method's return value type method name(){
 * java statement
 *     						}
 *Parameter passing of methods in java: passing by value both primitive data types (copy of value) and reference data types (value reference)
 *     
 * class is an object type
 *     
 * Template: write reality into the program
 * So java programs are organized in classes
 * The keyword class defines a custom data type
 *     		
 * Write a class template: A class is a template, an abstract concept that specifies the properties and methods that an object will have
 *[1] Write a type template using the class keyword
 *[2] Write the properties of the class
 *[3] Method of writing class
 *     
 * Use template:
 * [1] Create an instance of a class through a class
 * [2] Use objects to assign values ​​to properties
 * [3] Use the object to call the method
 *     
 *     
 * Method overloading:
 * is a way for classes to handle different types of data in a uniform way
 *     
 * Multiple functions/methods with the same name: exist at the same time, with different parameters/number/type (same name and different parameters)
 *
 */
public class Person { //[1] Write the type
		//[2] Write the properties of the class
		String name; //declare a member variable name, the default value is null
		int age; //declare a member variable age, the default value is 0
		char gender; //declare a member variable gender, the default value is blank

	
	//[3] Method of writing class
	public  void info(){
		System.out.println("My name is: "+name+", this year: "+age+", it is a "+gender+" sex.");
	}
	
	// no-argument constructor
	public Person(){ //When there is no parameterized structure written, the system will default to a parameterless structure. Once there are parameters written by hand, the system will no longer default.
			
	}
	
	// constructor with parameters
	public Person(String name,int age,char gender){
		this.name = name;
		this.age = age;
		this.gender = gender;
		//this: represents the current object, you can assign properties in the method to member variables (member properties)
	}
	
	
	// main method
	public static void main(String[] args) {
		//[1] Create object --" class name object name = new class name ();
		Person p1 = new Person();
		Person p2 = new Person("Flowers cross the horizon", 18, 'male');   
		
		//[2] Assign a value to the attribute --" object name. attribute = value;
		p1.name = "Mo Xiaohan";
		p1.age = -12;   
		p1.gender ='man';
		
		//[3]Using method --" object name.method name();
		p1.info();
		p2.info();
	}
}