一、类的定义和属性的getter、setter方法
1.类的定义使用class关键字
2.类中的属性默认实现了getter和setter方法(eg:Person中的age属性),如果要修改类中属性的getter和setter方法，参考Person类中name属性
3.只有可变属性才会有setting
class Person() {
var age:Int=0
var name: String = "unknow"
get() = field.capitalize()
set(value) {
field = value.trim()
}
}
二、构造函数
三、初始化顺序
1.主构造函数声明的属性
2.类级别的属性按声明属性依次赋值
3.init初始化代码块里的属性赋值和函数调用
4.次构造函数里的属性赋值和函数调用
注意：init代码块中用到的属性需要再init代码块之前声明，因为kotlin的编译时自上而下的
class Student(_name:String,val age:Int){
var name = _name
var score = 10
private val hobby="music"
val subject:String
init {
println("initializing student")
subject ="math"
}
constructor(_name:String):this(_name,10){
score = 20
}
}
//编译成java代码
public Student(@NotNull String _name, int age) {
Intrinsics.checkNotNullParameter(_name, "_name");
super();
//柱构造函数的属性
this.age = age;
//类级别的属性赋值
this.name = _name;
this.score = 10;
this.hobby = "music";
//init{}代码块
String var3 = "initializing student";
boolean var4 = false;
System.out.println(var3);
//init代码块中的属性赋值
this.subject = "math";
}
public Student(@NotNull String _name) {
Intrinsics.checkNotNullParameter(_name, "_name");
this(_name, 10);
//次构造函数中的属性赋值
this.score = 20;
}
在次构造函数Student(@NotNull String _name)中又调用了主构造函数this(_name, 10)
四、延迟初始化lateinit
1.lalteinit约定在使用该变量之前初始化
2.只要无法确认lateinit变量是否完成初始化，可以执行isInitialized检查
class Student(val age: Int) {
lateinit var subject: String
fun ready(){
subject = "math"
}
fun battle(){
if (::subject.isInitialized){
println(subject)
}
}
}
五、惰性初始化 lazy
class Student(val name:String) {
//属性被调用的时候执行
private val subject:String by lazy{
initSubject()
}
//调用构造函数的时候执行
private val subject2:String = initSubject()
fun initSubject():String{
Log.i("AAA","loading init subject")
return "Math"
}
}
六、object关键字
1.定义一个静态类
2.定义一个匿名类
3.定义一个伴生对象
七、嵌套类
在其他类中调用的时候如下
fun testJunior(){
val juniorStudent = Student.JuniorStudent("Jack")
}
class Student(val name:String) {
class JuniorStudent(val name:String)
}
八、数据类
1.数据类 是专门设计用来存储数据的类
2.数据类提供了toString()的个性化实现
3.==符号默认情况下，比较对象就是比较他们的引用值
4、copy函数调用的是主构造函数，在次构造函数中赋值的属性值实际并没有赋值，需要主动赋值
data class Teacher(val name:String)
转义为Java代码如下，默认实现了toString()、equals()、hashCode()、copy()方法,同时实现了component1()用于结构语法
public final class Teacher {
@NotNull
private final String name;
@NotNull
public final String getName() {
return this.name;
}
public Teacher(@NotNull String name) {
Intrinsics.checkNotNullParameter(name, "name");
super();
this.name = name;
}
@NotNull
public final String component1() {
return this.name;
}
@NotNull
public final Teacher copy(@NotNull String name) {
Intrinsics.checkNotNullParameter(name, "name");
return new Teacher(name);
}
// $FF: synthetic method
public static Teacher copy$default(Teacher var0, String var1, int var2, Object var3) {
if ((var2 & 1) != 0) {
var1 = var0.name;
}
return var0.copy(var1);
}
@NotNull
public String toString() {
return "Teacher(name=" + this.name + ")";
}
public int hashCode() {
String var10000 = this.name;
return var10000 != null ? var10000.hashCode() : 0;
}
public boolean equals(@Nullable Object var1) {
if (this != var1) {
if (var1 instanceof Teacher) {
Teacher var2 = (Teacher)var1;
if (Intrinsics.areEqual(this.name, var2.name)) {
return true;
}
}
return false;
} else {
return true;
}
}
}
九、结构声明
1.数据类直接支持结构语法
fun main() {
val (name, age, subject) = Teacher("Jack", 28, "Math")
println("$name--$age--$subject")
}
class Teacher(private val name: String, private val age: Int, private val subject: String) {
operator fun component1() = name
operator fun component2() = age
operator fun component3() = subject
}
十、枚举类 emun class
enum class LicenseStatus(){
UnQualified,
Learning,
Qualified;
var licenseId:String=""
}
十一、密封类 sealed class
密封类可以定义一个类似于枚举类的ADT,可以有若干个子类，要继承密封类，这些子类必须和它定义在用一个文件中。相对枚举类，密封类可以更加灵活的控制子类的特殊性。
sealed class LicenseStatus{
object UnQualified:LicenseStatus()
object Learning:LicenseStatus()
//特殊属性 licenseId
class Qualified(val licenseId:String):LicenseStatus()
}
十二、接口
interface OnItemClickListener {
fun onItemClick(view: View)
}
十三、抽象类abstract
abstract class Human(val age:Int){
abstract fun eat()
}
class American(val name:String, age:Int):Human(age) {
override fun eat() {
Log.i("AAA","I have hamburger")
}
}
