基本类型
Kotlin 只有Int，不区分int和Integer，编译器自动区分装箱和非装箱类型
不可隐式转换
java中将int值赋给Long类型，可以自动转换，kotlin会提示错误
val anInt: Int = 5
val aLong: Long = anInt //IDE会提示错误
val anLong: Long = anInt.toLong()
字符串的比较
‘==’ 与equals方法等价，用于比较内容
val string:String = "Hello"
val fromChars:String = String(charArrayOf('H','e','l','l','o'))
fun main(args: Array) {
print(string == fromChars)// true
print(string === fromChars) // false
}
public open operator fun equals(other: Any?): Boolean
而在kotlin中与Java的‘ == ’ 操作符等价的是 ‘===’，比较对象是否相同
字符串模板（拼接字符串）
Java中
val arg1:Int = 3
val arg2:Int = 2
println(""+arg1+" + "+arg2+" = "+(arg1+arg2))
而在kotlin中
println("$arg1 + $arg2 = ${arg1+arg2}")
打印结果会一模一样，但看起来会优雅很多。后面得跟上花括号{}，而不是括号()。
转义字符
- 如果要打印 Hello "Shaoxia",需要在"前面加上反斜杠“\”
//Hello "Shaoxia"
val sayHello : String = "Hello\"Shaoxia\""
println(sayHello)
- $的特殊化
//打印 $1000
val salary: Int = 1000
println("$1000")//①
println("$$salary")//②
//打印 $salary
println("\$salary")//③
①与②的执打印果完全一样,③加了反斜杠把$转为了字符
image
- 输入原始字符串
使用三个引号包起来，可以无视转义字符，输出原始数据
val rawString:String = """
\t
\n
\t
""""
println(rawString)
输出结果
image
类与对象
构造与初始化
创建一个MeiZi类，包含了构造函数
class MeiZi(var character:String,var appearance: String ,var voice: String)
这个构造函数省略了constructor和{},它与下面的两条语句等价
class MeiZi constructor(var character:String,var appearance: String ,var voice: String)
class MeiZi constructor(var character:String,var appearance: String ,var voice: String){}
如果要做初始化操作，可以重写init()函数，kotlin 构造对象不用像Java需要new关键字，直接调用构造函数即可
class MeiZi constructor(var character: String, var appearance: String, var voice: String) {
init {
println("new了一个妹子，这个妹子性格:$character,外貌$appearance,声音$voice")
}
}
fun main(args: Array) {
val meiZi: MeiZi = MeiZi("温柔", "甜美", "动人")
}
输出结果
image
继承
- 继承不再像Java需要extend关键字，而是用冒号“:”来取代
- 所有类继承于Any类
注意，子类的构造参数前面不能写var,IDE会提示'xxx' hides member of supertype 'XXX' and needs 'override' modifier，下面错误示范
class MeiZi(var character: String, var appearance: String, var voice: String): HuMan(character, appearance, voice)
正确例子
class MeiZi(character: String, appearance: String, voice: String): HuMan(character, appearance, voice)
class Man(character: String, appearance: String, voice: String): HuMan(character, appearance, voice)
open class HuMan(var character: String, var appearance: String, var voice: String) {
init {
println("new了一个${this.javaClass.simpleName}，这个妹子性格:$character,外貌$appearance,声音$voice")
}
}
fun main(args: Array) {
val meiZi: HuMan = MeiZi("温柔", "甜美", "动人")
val man: HuMan = Man("粗鲁", "彪悍", "洪亮")
val huMan: HuMan = HuMan("豪爽", "清新", "撩人")
}
输出
image
- Java判断一个对象是否是类的实例用instanceof，而Kotlin用is
val meiZi: MeiZi = MeiZi("温柔", "甜美", "动人")
println(meiZi is HuMan) // true