Spark学习使用笔记 - Scala篇（3）- 对象

field

class Counter {
//field必须初始化，为了知道类型
//会自动生成private的getter还有private的setter
//setter和getter并不是getValue()和setValue()这样，而是value(),value_=()这样
private var value = 0

def increment() = {
value += 1
}

def current() = value

//类私有field可以访问
def largerThan(a: Counter): Boolean = {
value > a.value
}

//对象私有field别的对象无法访问
private[this] var name = "test"

def setName(name: String) = {
this.name = name
}

//会自动生成public的getter和setter
var times = 0
//会自动生成public的getter
val alloc = "hash"

}

object Counter1 {
val counter = new Counter
def testClass = {
//习惯上取值器不加括号
println(counter.current)//输出：0
//习惯上改值器加括号
counter.increment()
println(counter.current)//输出：1

val counter2 = new Counter
println(counter.largerThan(counter2))//输出：true
}
}

Constructor

//main constructor
class Person(val name: String, var age: Int, var salary: Int) {
//主构造器会执行所有语句
println("Main constructor is called!")

//多态构造器
def this(name: String, age: Int) {
this(name, age, 0)
}

def description = "Name: " + name + ", Age: " + age + ", Salary: " + salary
}

object Person1 {
def test = {
val person = new Person("zhxhash", 24, 20000)//输出：Main constructor is called!
println(person.description)//输出：Name: zhxhash, Age: 24, Salary: 20000

val person2 = new Person("zhxdick", 15)//输出：Main constructor is called!
println(person2.description)//输出：Name: zhxdick, Age: 15, Salary: 0
}
}

练习：

object Exercise {

class Counter(private var value: Int = 0) {
def increment() = {
if (value == Int.MaxValue)
value = 0
else
value += 1
}

def current = value
}

def ex01 = {
val counter = new Counter(Int.MaxValue)
counter.increment()
println(counter.current)//输出：0
}

class BankAccount(private var balance: Double) {
def currentBalance = balance

def deposit(value: Double) = {
balance += value
}

def withdraw(value: Double) = {
balance -= value
}
}

def ex02 = {
val bankAccount = new BankAccount(100000)
bankAccount.deposit(99)
bankAccount.withdraw(88)
println(bankAccount.currentBalance)//输出：100011.0
}

class Time(private val hours: Int, private val minutes: Int) {
if (hours < 0 || hours > 23 || minutes < 0 || minutes > 59)
throw new IllegalArgumentException()

def before(other: Time): Boolean = {
(hours > other.hours) || ((hours == other.hours) && (minutes > other.minutes))
}

def description = "[" + hours + ":" + minutes + "]"
}

def ex03 = {
val time = new Time(13, 59)
val time2 = new Time(13, 25)
val time3 = new Time(14, 25)

println(time.description + time2.description + time.before(time2))//输出：[13:59][13:25]true
println(time.description + time3.description + time.before(time3))//输出：[13:59][14:25]false
}
}