【Kotlin】Kotlin笔记3-面向对象编程1(类与对象,继承,构造函数)

ゞ浴缸里的玫瑰 2022-11-16 04:50 238阅读 0赞

### Kotlin笔记-面向对象编程1-类与对象,继承,构造函数 ###

**3.1 面向对象编程**

*  **类与对象**

> **类:** 对事物的一种封装(人),通常是名词

> **字段:** 类属性(姓名,年龄),通常是名词

> **函数:** 类行为(吃饭,睡觉),通常是动词

> **class**

`Example:`

class Person {
        var name = ""
        var age = 0
    
        fun eat() {
            println("$name is eating. He is $age years old.")
        }
    }

*实例化*

val p=Person()

fun main() {
        val p=Person()
        p.name="Jack"
        p.age=19
        p.eat()
    }

--------------------

*  **继承**

`Example:`

class Student : Person1() {
        var sno = ""
        var grade = 10
    }

> **open**

open class Person1 {
        var name = ""
        var age = 0
        fun eat() = println("$name is eating. He is $age years old.")
    }

--------------------

*  **构造函数**

1.  **主构造函数**

*主构造函数:没有函数体*

class Student1(val sno: String, val grade: Int) : Person1() {
    }

val student = Student1("001", 100)

> **init**

*主构造函数逻辑实现*

class Student1(val sno: String, val grade: Int) : Person1() {
        init {
            println("sno is $sno")
            println("grade is $grade")
        }
    }

*主类构造函数必须调用父类构造函数实现方案*

open class Person2(val name: String, val age: Int) {
        fun eat() = println("$name is eating. He is $age years old.")
    }

class Student2(val sno: String, val grade: Int, name: String, age: Int) : Person2(name, age) {
        init {
            println("sno is $sno")
            println("grade is $grade")
        }
    }

val student1=Student2("001",100,"Tom",21)

1.  **次构造函数**

<table> 
 <thead> 
  <tr> 
   <th>序号</th> 
   <th>一些特性</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>1</td> 
   <td>任何一个类只能有一个主构造函数,但是可以有多个次构造函数</td> 
  </tr> 
  <tr> 
   <td>2</td> 
   <td>次构造函数可以用来实例化一个类,并且它有函数体</td> 
  </tr> 
  <tr> 
   <td>3</td> 
   <td>当一个类既有主构造函数,又有次构造函数,所有次构造函数必须调用主构造函数(包括间接接口)</td> 
  </tr> 
 </tbody> 
</table>

> **constructor**

`Example:`

class Student3(val sno: String, val grade: Int, name: String, age: Int) : Person2(name, age) {
        constructor(name:String,age:Int):this("",0,name,age)
    
        constructor():this("",0)
    }

*实例化*

val student4=Student3()
    val student5=Student3("Jack",19)
    val student6=Student3("001",100,"Jack",19)

1.  **特殊情况**

`类中只有次构造函数,没有主构造函数`

class Student4:Person2{
        constructor(name: String,age: Int):super(name,age){
        }
    }

--------------------

**q(≧▽≦q):Kotlin新特性**

1.  参数默认值可以替代次构造函数的功能