1. 改进点/基础
//安全判空
val length = text?.length;
//类型转换
if (object is Car) {
var car = object as Ca
}
//操作符变化
& and
| or
^ xor
>> shr
<< shl
//打印日志
print("123123")
println("asdassda")
2. 字符串
//多行字符串
val xx = """asdasdasd
asdasdsd """;
//字符串模版
var a = 1; val s1 = "a is $a"
4. 语法
var name = "123"; //可变变量
val name = "asdasd"; //不可变量，相当于java的final
var name: String = ...;
4.1 function
//定义function
fun sum(a: Int, b: Int): Int {
return a + b;
}
//默认参数
fun read(b: Array<Byte>, off: Int = 0, len: Int = b.size) {
}
//可变参数
fun <T> asList(vararg ts: T): List<T> {
val result = ArrayList<T>()
for (t in ts) // ts is an Array
result.add(t)
return result
}
val a = arrayOf(1, 2, 3)
//扩展对象上的function(替换代理模式)， 待扩展对象+方法名+返回值
fun Any?.funExt(): String {
if (this == null) return "null"
return toString()+"11111";
}
val str = "SSSS"; println (str.funExt());
//若返回值可能为null， 必须显示定义，否则运行时报错
fun parseInt(str: String): Int? {
}
4.2 属性
//扩展属性
val <T> List<T>.lastIndex: Int{
get() = size - 1
}
4.3 Lambdas
//lambdas表达式定义
//单个入参时，默认it
val sum = { x: Int, y: Int -> x + y };
//高阶函数 函数作为方法入参
//示例1--
fun <T, R> List<T>.map(transform: (T) -> R): List<R> {
val result = arrayListOf<R>()
for (item in this)
result.add(transform(item))
return result
}
//调用方式： val doubled = ints.map { value -> value * 2 }
或是 ints.map { it * 2 }
//示例2--内联函数
fun <T> max(collection: Collection<T>, less: (T, T) -> Boolean): T? {
var max: T? = null
for (it in collection)
if (max == null || less(max, it))
max = it;
return max
}
//调用： max(strings, { a, b -> a.length < b.length })
//未使用的参数可使用_代替
map.forEach { _, value -> println("$value!") }
5. Class
5.1 Class类和继承
//定义
class Invoice { }
或 class Person(val firstName: String, val lastName: String, var age: Int) {
// ...
}
//构建函数，一个主，多个次构造函数
//可自带默认参数
class Customer(val customerName: String = "")
//主构造函数是class声明的一部分, 构造函数默认public
class Customer(name: String) {
init {
logger.info("Customer initialized with value ${name}")
}
}
class DontCreateMe private constructor () { } //构造方法置为private
//次构造函数,可多个
class Person(val name: String) {
constructor(name: String, parent: Person) : this(name) {
parent.children.add(this)
}
}
//继承
class MyView : View {
constructor(ctx: Context) : super(ctx)
constructor(ctx: Context, attrs: AttributeSet) : super(ctx, attrs)
}
//覆写方法--overide
//kotlin中重写必须明确指定，使用open声明(否则编译报错)可被重写，open的fun必须包含在open的class中
open class Base {
open fun v() {}
fun nv() {}
}
class Derived() : Base() {
override fun v() {}
}
//覆写规则
open class A {
open fun f() { print("A") }
fun a() { print("a") }
}
interface B {
fun f() { print("B") } // interface members are 'open' by default
fun b() { print("b") }
}
class C() : A(), B {
// The compiler requires f() to be overridden:
override fun f() {
super<A>.f() // call to A.f()
super<B>.f() // call to B.f()
}
}
//覆写property
//Abstract
5.2 property和Fields
class Address { var name: String = ... };
//改写getter和setter方法
val isEmpty: Boolean get() = this.size == 0;
var stringRepresentation: String
get() = this.toString()
set(value) {
setDataFromString(value) // parses the string and assigns values to other properties
}
//private setter
var setterVisibility: String = "abc"
private set
5.3 interface接口
interface MyInterface {
fun bar()
fun foo() { }
}
class Child : MyInterface {
override fun bar() {
// body
}
}
5.4 Data Classes 只包含数据的Class
//针对此种模型，kotlin额外定义了一些扩展方法
-- equals()/hashCode() pair,
-- toString() of the form "User(name=John, age=42)",
data class User(val name: String = "", val age: Int = 0); //示例1
//copy方法
val jack = User(name = "Jack", age = 1)
val olderJack = jack.copy(age = 2)
5.5 泛型Generics
6. 逻辑操作
6.1 for循环
for (item in items) {
println(item)
}
6.2 退出循环-break label
//退出多重for循环
lxx@ for (i in 1..10) {
for (j in 1..10) {
println("x=$i;y=$j");
if (i == 5) break@lxx;
}
}
//forEach中退出当次循环
mutableListOf(1, 2, 3,4).forEach {
if (it == 2) return@forEach
print(it);
}
6.3 when
//替换switch Case
var grade = when (score) {
9, 10 -> "Excellent"
in 6..8 -> "Good"
4, 5 -> "Ok"
in 1..3 -> "Fail"
else -> "Fail"
}
when {
"orange" in items -> println("juicy")
"apple" in items -> println("apple is fine too")
}
6.4替换3目运算符
val text = if (x > 5)
"x > 5"
else "x <= 5"
fun maxOf(a: Int, b: Int) = if (a > b) a else b
15. 其它
15.1 main函数
class KotlinTe { }
fun main(args: Array<String>) {
var output: String? = "123123";
println(ou);
}
15.2 与java互相调用
//java中调kotlin
1).调用相同
//kotlin中调java
1).kotlin中无new关键字，其它属性-方法调用相同
15.3 默认导入
kotlin.*; kotlin.annotation.*; kotlin.collections.*;
kotlin.comparisons.* (since 1.1); kotlin.io.*; kotlin.ranges.*;
kotlin.sequences.*; kotlin.text.*;
java.lang.*; kotlin.jvm.*;
15.4 kotlin的maven依赖
IDEA maven工程中创建kt文件时会提示增加kotlin依赖，默认即可。(包括dependency和build两类标签)