简单的类

给类增加字段和方法

创建对象

编译和执行

class Counter{
    private var value = 0
    def increment(): Unit ={ value += 1}
    def current(): Int ={value}
}
val mycounter = new Counter
mycounter.increment()
println(mycounter.current)

在命令行输入

scala test02.scala

就可以实现功能
也可以使用scala解释器来执行相应的程序 （:load） 在解释器中：代表命令指令

问题：为什么不用scalac编译
这个例程无法通过

修改成为单例对象：


设置成带参数传入

class Counter{
    private var value = 0
    def increment(step : Int): Unit ={ value += step}
    def current(): Int ={value}
}
object mycounter
{
    def main(args:Array[String]){
    val mycounter = new Counter
    mycounter.increment(5)
    println(mycounter.current())
    }
}

getter和setter方法

class Counter{
    var value = 0
    def increment(step : Int): Unit ={ value += step}
    def current(): Int ={value}
}
object mycounter
{
    def main(args:Array[String]){
    val mycounter = new Counter
    println(mycounter.value)
    mycounter.value=3
    mycounter.increment(5)
    println(mycounter.current())
    }
}

注意：

不要乱设置公有属性！
修改 使用value和value_方法

class Counter{
    private var privatevalue = 0
    def value = privatevalue
    def value_=(newValue : int){
        if(newValue > 0) privateValue = newValue
        }
    def increment(step : Int): Unit ={ value += step}
    def current(): Int ={value}
}
object mycounter
{
    def main(args:Array[String]){
    val mycounter = new Counter
    println(mycounter.value)
    mycounter.value=3  //调用value_这个方法
    mycounter.increment(5)
    println(mycounter.current())
    }
}

构造器

class Counter{
    private var value = 0
    private var name = ""
    private var mode = 1
    def this(name : String){   //第一个辅助构造器
        this()    //调用主构造器
        this.name =name
    }
    def this(name : String, mode : Int){ //第二个辅助构造器
        this(name)  //调用前一个辅助构造器
        this.mode = mode
    }
    def increment(step : Int): Unit ={ value += step}
    def current(): Int ={value}
    def info() : Unit = {printf("name: %s and mode is %d\n",name,mode)}
}
object mycounter
{
    def main(args:Array[String]){
    val mycounter1 = new Counter   //调用主构造器，参数默认为空
    val mycounter2 = new Counter("Runner")  //第一个辅助
    val mycounter3 = new Counter("Timer",2)  //第二个辅助，中间会调用第一个辅助构造器
    mycounter1.info
    mycounter1.increment(1)
    printf("Current value is %d\n",mycounter1.current())
    mycounter2.info
    mycounter2.increment(2)
    printf("Current value is %d\n",mycounter2.current())
    mycounter3.info
    mycounter3.increment(1)
    printf("Current value is %d\n",mycounter3.current())
    }
}

每个类都是主构造器的

主构造器

scala中的主构造器改写

class Counter(val name: String , val mode: Int){  //可以直接将参数写在主构造器中
    private var privatevalue = 0
    def value = privatevalue
    def value_=(newValue : int){
        if(newValue > 0) privateValue = newValue
        }
    def increment(step : Int): Unit ={ value += step}
    def current(): Int ={value}
    def info(): Uint = {printf("name is %s and mode is %d",name,mode)} 
    //可以直接使用name和mode而不用在类里面进行定义，会自动生成这两个字段
}
object mycounter
{
    def main(args:Array[String]){
    val mycounter = new Counter
    println(mycounter.value)
    mycounter.value=3  //调用value_这个方法
    mycounter.increment(5)
    println(mycounter.current())
    }
}