变量	String yourPast = "Good Java Programmer";	val yourPast : String = "Good Java Programmer" val yourPast = "Good Java Programmer" var yourFuture = "Good Java Programmer" 自动类型推断；可变、不可变变量 class Money(amount:Int) amount不是成员变量 class Money(val amount:Int) val notMuch = new Money(2) notMuch.amount class Money(var amount:Int) val notMuch = new Money(2) notMuch.amount=3
case classes	public class Money { private Integer amount; private String currency; public Money(Integer amount, String currency) { this.amount = amount; this.currency = currency; } public Integer getAmount() { return amount; } public void setAmount(Integer amount) { this.amount = amount; } public String getCurrency() { return currency; } public void setCurrency(String currency) { this.currency = currency; } @Override public int hashCode() { int hash = 5; hash = 29 * hash + (this.amount != null ? this.amount. hashCode() : 0); hash = 29 * hash + (this.currency != null ? this.currency. hashCode() : 0); return hash; } @Override public boolean equals(Object obj) { if (obj == null) { return false; } if (getClass() != obj.getClass()) { return false; } final Money other = (Money) obj; return true; } @Override public String toString() { return "Money{" + "amount=" + amount + ", currency=" + currency + '}'; } public Money add(Money other) { return new Money(this.amount + other.amount, this.currency); } }	case class Money(amount:Int=1, currency:String="USD")  two immutable fields the fields declared in Scala classes are public case class Money(private val amount: Int, private val currency: String) to make them private instead, or used  var instead of  val to make the fields mutable. val defaultAmount = Money() val fifteenDollars = Money(15,"USD") val fifteenDollars = Money(15) val someEuros = Money(currency="EUR") case class Money(val amount:Int=1, val currency:String="USD"){ def +(other: Money) : Money = Money(amount + other.amount) } Money(12) + Money(34)
collections	Scala collections are, by default, immutable val numbers = List(1,2,3,4,5,6) val reversedList = numbers.reverse val onlyAFew = numbers drop 2 take 3 cons operator val numbers = 1 :: 2 :: 3 :: 4 :: 5 :: 6 :: Nil val simpleList = Nil.::(6) val twoElementsList = List(6).::(5) 列表串接 val concatenatedList = simpleList ::: twoElementsList val things = List(0,1,true) AnyVal val things = List(0,1,true,"false") Any 复杂对象列表 val amounts = List(Money(10,"USD"),Money(2,"EUR"),Money(20,"GBP"), Money(75,"EUR"),Money(100,"USD"),Money(50,"USD")) Filter val euros = amounts.filter(money => money.currency=="EUR") val euros = amounts.filter(x => x.currency=="EUR") val euros = amounts.filter(_.currency=="EUR") partition val allAmounts = amounts.partition(amt => amt.currency=="EUR") Tuples val euros = allAmounts._1 val everythingButEuros= allAmounts._2 val (euros,everythingButEuros) = amounts.partition(amt => amt.currency=="EUR")
Map	Map amounts = new HashMap<String,Integer>(); amounts.put("USD", 10); amounts.put("EUR", 2);	val wallet = Map( "USD" -> 10, "EUR" -> 2 ) val someEuros = wallet("EUR") Option类型 val mayBeSome

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