Although I used Kotlin for a while before, but looking back, I didn’t make notes in this area, so I simply recorded it systematically.
base over
- Getting Started with Kotlin Basics - Variables, Functions (Methods), Objects, Inheritance, Interfaces
- Introduction to Kotlin Basics - Static Variables, Constants And Static Functions, Methods
- Kotlin Practical Basics - Setting Click Events, Activity Jumps, and Passing Values
- Kotlin combat basics - Activity, Fragment transfer parameters
自语：Kotlin语法糖真是秀儿，话说，并不是Java不如Kotlin，而是Google在推属于android自己的语言
This article mainly records some Kotlinbasic usage methods for your convenience. 快速从Java转战到KotlinFor simplicity and clarity, I will 综合Java、Kt的不同使用record them together. If you are interested, you can also go to Google's Kotlin documentation to learn~
How to declare variables?
Java
String data = "宋老三";
Kotlin
在Kotlin声明变量时，通常有俩种方式
varassignment can be modifiedvalOnly supports initialization assignment, refer to Javafinalkeywords
Kotlin Regular
var dataVar: String = "宋老三"
val dataVal: String = "宋老三"
Simplified version of Kotlin ( Kt 自带类型推断features, variable types can be inferred based on assigned data)
var dataVar = "宋老三"
val dataVal = "宋老三"
How to declare methods and functions?
函数又称为方法，是具有特定功能的一段独立程序。
We are declaring Java中经常将函数说成方法，在Kotlin中称为函数更多一些the main use of the function , the following is generallyfun函数函数组成结构
函数声明 函数名称（[参数名称：参数类型，参数名称：参数类型]）：返回值类型{
执行语句
…
return 返回值
}
- Function Declaration: Function declarations in Kotlin use keywords
fun. - Function name:
每一个函数都有函数名称, convenient to use when calling the function. - Parameter type: used to limit when calling a function
传入参数的数据类型. - Parameter name: is a
变量, used for接收调用函数时传入的数据. - Return value type: for
限定函数返回值的数据类型. - Return value: was
return语句返回的值，该值会返回给调用者.
no parameter no return value
Java
public void test() {
}
Kotlin
fun test() {
println("这是一个无参无返回值的函数")
}
返回 Unit类型，可不写
fun test(): Unit {
println("这是一个无参无返回值的函数")
}
Return value without parameter
Kotlin
fun test(): String {
return " 这是一个无参有返回值的函数"
}
With parameters but without return value
Java
public void test(int num1) {
}
Kotlin
fun test(num1: Int) {
println("这是一个无参无返回值的函数")
}
have parameters and return value
Java
public int test(int num1, int num2) {
return num1 + num2;
}
Kotlin
注意：档方法需要return返回值时，在方法后声明返回类型
fun test(num1: Int, num2: Int): Int {
return num1 + num2
}
single expression function
Syntactic sugar - can be used directly when the return value is only one line= 返回
fun test(num1: Int, num2: Int): Int = num1 + num2
How to create objects?
Java
Create a class (including set method, get method, construction method)
public class Dream {
public String what;
public String time;
public Dream() {
super();
}
public Dream(String what, String time) {
this.what = what;
this.time = time;
}
public String getWhat() {
return what;
}
public void setWhat(String what) {
this.what = what;
}
public String getTime() {
return time;
}
public void setTime(String time) {
this.time = time;
}
}
create object
Dream info = new Dream("Life","2022");
Kotlin
create class( 包含set方法、get方法、有参构造方法)
open class Dream {
//父类无参的次构造器
constructor() {
println("无参构造器")
}
//父类无参的次构造器
constructor(what: String, time: String) {
println("无参构造器")
}
}
Simplified writing, but there is no no-argument construction
open class Dream(var what: String, var time: String) {
}
create object
var dream: Dream = Dream("Life", "2022")
//类型推导
var dream = Dream("Life","2022")
How class inheritance?
Java
public class Son extends Dream{
}
Kotlin
class Son : Dream(){
}
How to implement the interface?
Java
create interface
public interface DreamListener {
public void gogo();
}
interface implementation
实现方式 → implements +接口
import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
public class MainActivity extends AppCompatActivity implements DreamListener {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
@Override
public void gogo() {
}
}
Kotlin
create interface
interface DreamListener {
fun gogo()
}
interface implementation
实现方式 → ：+接口
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
class MainActivity : AppCompatActivity(), DreamListener {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
}
override fun gogo() {
}
}