Scala是一門函數式的面向對象的語言，它運行在Java虛擬機上。
eg1、
示例代碼：
scala>var helloWorld = "hello" + " world"
println(helloWorld)
scala>val again = " again"
helloWorld = helloWorld + again
println(helloWorld)
輸出：
hello world
hello world again
eg2、定義函數 def
示例代碼：
def square(a: Int) = a * a
def squareWithBlock(a: Int) = { a * a}
val squareVal = (a: Int) => a * a （這裡是將Int整數a映射為a*a的函數）
def addOne(f: Int => Int, arg: Int) = f(arg) + 1（這裡的=>表示所映射的類型，這就表示這個參數要是一個參數為int類型，返回的類型也是int 的方法）
println("square(2):" + square(2))
println("squareWithBlock(2):" + squareWithBlock(2))
println("squareVal(2):" + squareVal(2))
println("addOne(squareVal,2):" + addOne(squareVal, 2))
輸出結果：
square(2):4
squareWithBlock(2):4
squareVal(2):4
addOne(squareVal,2):5
eg3、
代碼實例：
import scala.reflect.io.File
import java.util.Scanner
def withScanner(f: File, op: Scanner => Unit) = { // 沒有返回值的默認返回的是Unit
val scanner = new Scanner(f.bufferedReader)
try {
op(scanner)
} finally {
scanner.close()
}
}
withScanner(File("/proc/self/stat"),
scanner => println("pid is " + scanner.next()))
其中widthScanner封裝了try-Catch塊，調用者不用再close了
返回結果：
pid is 6065
eg4、定義類
class Persion(val firstName: String, val lastName: String) { //通過class定義類，val來定義字段，在類中def定義類中的函數，其中firstName和lastName會自動生成get,set方法
private var _age = 0
def age = _age //這是一個方法
def age_=(newAge: Int) = _age = newAge
def fullName() = firstName + " " + lastName
override def toString() = fullName() //這是覆蓋toString方法
}
val obama: Persion = new Persion("Barack", "Obama") //用new的方式創建類
println("Persion: " + obama)
println("firstName: " + obama.firstName)
println("lastName: " + obama.lastName)
obama.age_=(51)
println("age: " + obama.age)
返回結果：
Persion: Barack Obama
firstName: Barack
lastName: Obama
age: 51
eg5、
運行實例：
def withClose(closeAble: { def close(): Unit }, //這裡是將{def close():Unit}這個方法作為一種類型
op: { def close(): Unit } => Unit) {
try {
op(closeAble)
} finally {
closeAble.close()
}
}
class Connection {
def close() = println("close Connection")
}
val conn: Connection = new Connection()
withClose(conn, conn =>
println("do something with Connection"))
運行結果：
do something with Connection
close Connection
eg6、柯裡化（currying）技術
def add(x:Int, y:Int) = x + y是普通的函數
def add(x:Int) = (y:Int) => x + y
是柯裡化後的函數，相當於返回一個匿名函數表達式。
def add(x:Int)(y:Int) = x + y
是簡化寫法
def withClose(closeAble: { def close(): Unit }) //小白一枚，還是沒有弄明白為什麼我創建這個方法時候總是無效的？？？
(op: { def close(): Unit } => Unit) {
try {
op(closeAble)
} finally {
closeAble.close()
}
}
class Connection {
def close() = println("close Connection")
}
val conn: Connection = new Connection()
withClose(conn)(conn =>
println("do something with Connection"))
eg7、泛型
def withClose[A <: { def close(): Unit }, B](closeAble: A)//這裡的A表示的是{def close():Unit}的子類型
(f: A => B): B =
try {
f(closeAble)
} finally {
closeAble.close()
}
class Connection {
def close() = println("close Connection")
}
val conn: Connection = new Connection()
val msg = withClose(conn) { conn =>
{
println("do something with Connection")
"123456"
}
}
println(msg)
返回結果：
do something with Connection
close Connection
123456
eg8 Traits 相當於java中的接口implements
trait ForEachAble[A] {
def iterator: java.util.Iterator[A]
def foreach(f: A => Unit) = {
val iter = iterator
while (iter.hasNext)
f(iter.next)
}
}
trait JsonAble {
def toJson() =
scala.util.parsing.json.JSONFormat.defaultFormatter(this)
}
val list = new java.util.ArrayList[Int]() with ForEachAble[Int] width JsonAble
list.add(1); list.add(2)
println("For each: "); list.foreach(x => println(x))
//println("Json: " + list.toJson())
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