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

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)

2. 次构造函数

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)

3. 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