Detailed explanation of Java object-oriented programming and objects

This article mainly introduces the Java language object-oriented programming ideas and detailed explanations of object instances. It is still very good. I will share it with you here and friends who need it can refer to it.

When beginners learn Java, object-oriented is difficult for people to understand, so today I will help you understand this idea in an extremely simple way.
First of all, let’s briefly explain the object-oriented idea.

Object-oriented:

The official language is very abstract, so we put aside the official explanations and definitions. Think about it, what do you have, right? ! We have a series of organs such as hands, feet, eyes, mouth and nose. Let’s think of the organs we have as our attributes. Whether we can be happy, angry, sad, laughing and cursing are our behaviors. Then the attributes we have plus the behaviors we have are called an object. .

Notice! ! We ourselves, an individual, are an object, because you are you and I am me. Although we have the same things, we are different. For example, you are taller than me and I have longer hair than you.

The next step is further. You and I are both human beings, and because you and I have similar things, we are both human beings. Human beings are the general term for people and are also an abstraction of similar objects.

Looking from the above: You and I are just two special cases of human beings, but aliens can also call us human beings. It can be seen that the specific manifestation or instance of a class is an object, and The abstraction or generalization of an object is a class.

The editor said it is so simple. How can it be done without using examples? Let’s use Java code to reflect the situation.

Let’s write down a person’s class. Note: Objects come from classes. Classes come first, objects come after them, and only when classes are instantiated.

The original code is not suitable. The editor has modified it as follows:

public class Person { 
String name; 
int age; 
String gender; 
public Person() { 
} 
Person(String name,int age,String gender){ 
this.name = name; 
this.age = age; 
this.gender = gender; 
System.out.println(this.name+"对象被创建了"+"，有"+this.age+"岁"+"，是"+this.gender+"的"); 
} 
public static void main(String[] args) { 
  Person p1 = new Person("张三", 18, "男"); 
  Person p2 = new Person("李四", 19, "女"); 
} 
}

Running result:

张三对象被创建了，有18岁，是男的
李四对象被创建了，有19岁，是女的

The above is the understanding of object-oriented.

Class:

The above editor has already mentioned that a class is an attribute plus a behavior, and the above code has already explained the attribute

In order to better explain the behavior, we will add the behavior of the class in Java——Method

package objectandclass; 
 
import java.awt.SecondaryLoop; 
 
public class Person { 
  String name; 
  int age; 
  String gender; 
  public Person() { 
     
  } 
  Person(String name,int age,String gender){ 
    this.name = name; 
    this.age = age; 
    this.gender = gender; 
    System.out.println(this.name+"对象被创建了"+"，有"+this.age+"岁"+"，是"+this.gender+"的"); 
  } 
   
  public void say(){ 
    System.out.println("我说我叫"+this.name+",别以为我不会说话，我会说很多话。"); 
  } 
   
}

The class has After adding the method, the object can also call this method. We say that at this time the object has some behavioral manifestations of the class.

public static void main(String[] args) { 
    Person p1 = new Person("张三", 18, "男"); 
    p1.say(); 
    Person p2 = new Person("李四", 19, "女"); 
    p2.say(); 
  }

Obviously: the result of the operation must be:

张三对象被创建了，有18岁，是男的
我说我叫张三,别以为我不会说话，我会说很多话。
李四对象被创建了，有19岁，是女的
我说我叫李四,别以为我不会说话，我会说很多话。

Let’s talk about the class Some characteristics of:

class, it has its own things and things for objects. Class things are members of the class.

The members of a class generally include initialization blocks, constructors, properties, methods, inner classes, and enumeration classes.

If it is something that belongs to a class (it can be called directly using the class name. member), use static call.

In fact, all class objects can be used, whether they are static or not, but if they are not modified with static, they are objects and can only be called by instantiated objects.

Needless to say about objects, just remember two points. To create an object, you must call the constructor.

The initialization block can be regarded as a special constructor, no parameters are passed in, and it will be called anyway when creating an object.

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