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开源软件名称（OpenSource Name）：githubhaohao/JavaToKotlin开源软件地址(OpenSource Url)：https://github.com/githubhaohao/JavaToKotlin开源编程语言(OpenSource Language)：Kotlin 84.5%开源软件介绍(OpenSource Introduction)：Java to Kotlin 语法清单时刻对新事物保持好奇心
Kotlin 简介Kotlin 来自于捷克一家牛逼软件研发公司 JetBrains ，很多优秀的 IDE，如 IntelliJ IDEA、PyCharm、WebStorm 等都是它的杰作，包括 Google 官方的 Android IDE -- Android Studio ，也是 IntelliJ IDEA 的插件版。 Kotlin 源于 JetBrains 的圣彼得堡团队，名称取自圣彼得堡附近的一个小岛 ( Kotlin Island ) ，JetBrains 在 2010 年首次推出 Kotlin 编程语言，并在次年将之开源。 Kotlin 的特点Kotlin 是一个基于 JVM 的编程语言，与 Java 有很深的渊源。它能与 Java 100% 互通，具备诸多 Java 尚不支持的新特性。Kotlin 可以编译成 Java 字节码，也可以编译成 JavaScript ，方便在没有 JVM 的设备上运行，可用于移动端以及 Web 开发，是一种全栈式开发语言。 Java to Kotlin下面是 Java to Kotlin 主要语法，以便于你快速认识 Kotlin 这门语言。 变量Java String lan = "Hello Kotlin";
final String lan = "Hello Kotlin";Kotlin var lan = "Hello Kotlin"
val lan = "Hello Kotlin"打印字符串Java System.out.print("Hello Kotlin");
System.out.println("Hello Kotlin");Kotlin print("Hello Kotlin");
println("Hello Kotlin");字符串模板Java String name = "haohao";
int age = 25;
String msg = "I am " + name + ", " + age + " years old.";
String text = "Hello Kotlin\n" +
"Hello Android\n" +
"Hello TensorFlow";Kotlin var name = "haohao";
var age = 25;
var msg = "I am $name , $age years old.";
var text = """
|Hello Kotlin
|Hello Android
|Hello TensorFlow
""".trimMargin()
// trimMargin() 去除连接符 `|`
空声明Java String name = null;Kotlin var name: String? = null // `?` 声明变量可为 null 判空Java if (name != null) {
int len = name.length;
}Kotlin name?.let{
val len = name.length
}逻辑表达式Java String y = x > 6 ? "x > 6" : "x <= 6";Kotlin var y = if (x > 6)
"x > 6"
else "x <= 6"类型判断及转换Java if (obj instanceof Person) {
Person p = (Person) obj;
}Kotlin if (obj is Person) {
var p = obj //智能转换
}区间Java if (value >= 0 && value <= 100) {
}
for (int i = 1; i <= 100 ; i++) {}
for (int i = 1; i < 100 ; i++) {}
for (int i = 100; i >= 0 ; i--) {}
for (int i = 1; i <= 100 ; i+=2) {}
for (int i = 100; i >= 0 ; i-=2) {}Kotlin if (value is 0..100) {
}
for (i in 1..100 ) {}
for (i in 1 until 100) {} // 半开区间：不包含 100
for (i in 100 downTo 0) {}
for (i in 1..100 step 2) {}
for (i in 100 donwTo 1 step 2) {}list 和 map ( 针对 Java 8 之前版本 )Java List<Integer> list = Arrays.asList(1, 2, 3, 4);
for(Integer value : list) {
System.out.println(value);
}
Map<Integer, String> map = new HashMap<>();
map.put(1, "Java");
map.put(2, "Kotlin");
map.put(3, "iOS");
map.put(4, "React Native");
Iterator<Map.Entry<Integer, String>> iterator = map.entrySet().iterator();
while (iterator.hasNext()) {
Map.Entry<Integer, String> entry = iterator.next();
System.out.println(entry.getKey() + " , " + entry.getValue());
}
Kotlin var list = listOf(1, 2, 3, 4);
list.forEach {
println(it)
}
var map = mapOf(1 to "Java", 2 to "Kotlin", 3 to "iOS", 4 to "React Native")
map.forEach { key, value ->
println("$key, $value")
}
// 或者
for ((key, value) in map) {
println("$key, $value")
}
开关语句Java int score = // some score
String grade;
switch (score) {
case 10:
case 9:
grade = "Excellent";
break;
case 8:
case 7:
case 6:
grade = "Good";
break;
case 5:
case 4:
grade = "Ok";
break;
case 3:
case 2:
case 1:
grade = "Fail";
break;
default:
grade = "Fail";
}Kotlin var score = // some score
var grade = when (score) {
9, 10 -> "Excellent"
in 6..8 -> "Good"
4, 5 -> "Ok"
in 1..3 -> "Fail"
else -> "Fail"
}流水线Java List<String> list = Arrays.asList("java", "c++", "Android", "Kotlin", "iOS");
for(int i = 0; i < list.size(); i++ ) {
list.set(i, "Hello " + list.get(i));
if (!list.get(i).contains("c")) {
System.out.println(list.get(i));
}
}
//输出：
// Hello java
// Hello Android
// Hello Kotlin
// Hello iOSKotlin var list = arrayOf("java", "c++", "Android", "Kotlin", "iOS")
list.map {
"Hello $it"
}.filter {
!it.contains("c")
}.forEach {
println(it)
}
//输出：
// Hello java
// Hello Android
// Hello Kotlin
// Hello iOS函数Java public final void func() {}
public final int func(int value) {
return 1 * value;
}Kotlin fun func() {}
fun func(value: Int): Int {
return 1 * value
}
// 或者
fun func(value: Int): Int = 1 * value类Java public final class Person {
private String name = null;
private int age = 25;
private Person() {
}
public Person(String name, int age) {
this.name = name;
this.age = age;
}
}Kotlin class Person private constructor() {
private var name: String? = null
private var age: Int = 25
constructor (name: String, age: Int): this() {
this.name = name
this.age = age
}
}静态方法（ 伴生对象 ）Java public final class Manager {
private Manager() {}
public static Manager getInstance () {
return new Manager();
}
}Kotlin class Manager private constructor() {
companion object {
fun getInstance(): Manager = Manager()
}
}
实体类Java public class Person {
public String name;
public age;
public Person(String name, int age) {
this.name = name;
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
Person person = (Person) o;
if (age != person.age) return false;
return name != null ? name.equals(person.name) : person.name == null;
}
@Override
public int hashCode() {
int result = name != null ? name.hashCode() : 0;
result = 31 * result + age;
return result;
}
@Override
public String toString() {
return "Person{" +
"name='" + name + '\'' +
", age=" + age +
'}';
}
}Kotlin data class Person(var name: String, var age: Int)
解构Java Person p = new Person("haohao", 25);
String name = p.getName();
String age = p.getAge();Kotlin var p = Person("name", 25)
var (name, age) = p接口Java interface Readable {
String getContent();
}public final class Book implements Readable {
@override
public String getContent() {
return "Hello";
}
} Kotlin // Kotlin 接口中可以设置抽象和非抽象方法,可以有属性但必须声明为抽象或提供访问器实现。
interface Readable {
fun getContent(): String
fun getVersion(): Int = 0
}class Book(): Readable {
override fun getContent(): String = "Hello"
override fun getVersion(): Int {
return super.getVersion()
}
}继承Java public class Person {
private String name = null;
public Person(String name) {
this.name = name;
}
public void sayHello() {
System.out.println("Hello");
}
public final void sayGood() {
System.out.println("Good");
}
}public final class Student extends Person {
private String school = null;
public Student(String name, String school) {
super(name);
this.school = school;
}
@Override
public void sayHello() {
super.sayHello();
System.out.println("Hello Student");
}
}Kotlin open class Person(private var name: String? = null) {
open fun sayHello() = println("Hello")
fun sayGood() = println("Good")
}class Student(private var school: String? = null, name: String): Person(name) {
override fun sayHello() {
super.sayHello()
println("Hello Student")
}
} 静态与非静态内部类Java public final class Outer {
private int bar = 100;
public static class Nester {
public final String foo() {
return "Hello Kotlin!";
}
}
public final class Inner {
public final int foo() {
return bar; // 可以访问外部类成员
}
}
}
System.out.println(new Outer.Nester().foo());
// System.out.println(new Outer().Inner().foo()); 不能在其他类中实例化非静态内部类Kotlin 全部评论
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