Object-oriented classes, objects 21

Object-oriented overview

java is object-oriented high-level programming language. Simple things can be considered to be a high degree of code to simulate the real world: the object oriented implementation.

Object-oriented of the most important two concepts: classes, objects.

Class of understanding

• Class is a description of common attributes and behavior of the same thing. Humans, like students, teachers, class, officials, businessmen.
  Simple to understand: The class is a description of the reality of things

The composition of the class

• Attributes (member variables): refers to the characteristics of things, such as: human (name, age, height, weight)
• Behavior (member method): refers to operations that things can be performed, such as: human (singing, dancing)

Objects

• Everything that exists objectively are all objects, so we often say things are objects.
• Objects are instances of real existence. Object == instance.

Class definition

Class usually seen two components:
the composition is determined by the class properties and behavior of two parts

• Properties: In a class by member variables to reflect
• Behavior: in the classes to reflect the methods by members

Class Definition Format:

修饰符 class 类名{
             // 1、成员变量：Field(描述类或者对象的属性信息的，例如：身高，体重，名称)
             // 2、成员方法: Method(描述类或者对象的行为信息的，例如：唱歌，跳舞，买票)
             // 3、构造器： Constructor(初始化类的一个对象出来)
             ....
        }

Class defined in claim

1, class name first letter capitalized recommendations to meet hump mode , can not use keywords, identifiers must be lawful and to be meaningful.
2, a Java file can define multiple classes, but only one class modified with public and public-modified class name, the file must be the name of the Java code, otherwise an error!
3, a Java code file a class can not be modified with the public, then the code file name can be freely
4, but it is recommended that a java file only defines one class.

E.g:

public class People {
    // 1、属性
    String name; // 名称
    int age ; // 年龄
    double height ; //身高
    double weight ; // 体重

    // 2、行为
    public void sing(){
        System.out.println("唱的真好!!");
    }

    public void jump(){
        System.out.println("跳的真美!!");
    }
}

Creating objects

Creating an object format:
name of the class object name = new class name ();
call the member variable format:
Object variable members
calling member methods format:
name of the object member method ();.

public class PeopleDemo {
    public static void main(String[] args) {
        // 1、创建对象的格式：
        // 类名 对象名称 = new 类名();
        People wuHao = new People();

        // 2、调用成员变量的格式：对象名.成员变量
        System.out.println(wuHao.name); // null
        wuHao.name = "吴昊"; // 赋值
        wuHao.age = 18 ; // 赋值
        wuHao.weight = 60; // 赋值
        wuHao.height = 180 ;// 赋值
        System.out.println(wuHao.name); // 吴昊
        System.out.println(wuHao.age);  // 18
        System.out.println(wuHao.weight); // 60.0
        System.out.println(wuHao.height); // 180.0

        // 3、调用成员方法的格式:对象名称.成员方法
        wuHao.sing();
        wuHao.jump();
    }
}

class People {
    // 1、属性
    String name; // 名称
    int age ; // 年龄
    double height ; //身高
    double weight ; // 体重
    // 2、行为
    public void sing(){
        System.out.println("唱的真好!!");
    }

    public void jump(){
        System.out.println("跳的真美!!");
    }
}

Note: Objects can directly assign themselves to another object, this address assignment, which will be another long modify a modification. With reference to the type of array bit like.

Student minGe = xuMin; // 把xuMin这个对象变量存储的地址赋值给了minGe变量

example:

public class StudentDemo {
    public static void main(String[] args) {
        Student xuMin = new Student();
        System.out.println(xuMin); // 6d03e736
        xuMin.name = "徐敏";
        xuMin.age = 18 ;
        System.out.println(xuMin.name); // 徐敏
        System.out.println(xuMin.age); // 18
        xuMin.study();
        xuMin.doHomeWork();

        System.out.println("-----------------------------------");
        Student minGe = xuMin; // 把xuMin这个对象变量存储的地址赋值给了minGe变量
        System.out.println(minGe); // 6d03e736
        minGe.name = "敏哥";
        System.out.println(xuMin.name); // 敏哥
        System.out.println(minGe.age);  // 18
        minGe.study();
        minGe.doHomeWork();
    }
}
class Student{
    // a.属性（成员变量）
    String name ;
    int age ;
    // b.行为（方法）：学习
    public void study(){
        System.out.println("好好学习，天天向上");
    }
    // c.行为（方法）：抄写代码
    public void doHomeWork(){
        System.out.println("写代码、写代码、写代码。");
    }
}