scala学习笔记(3)

1 类

(1)

scala把主构造函数放到类的定义中，让定义字段及相应方法变得简单起来。

class People(age: Int, name: String)

scala会自动将这个类变成public，默认的就是public. 如果我们将age这个字段设为 val age: Int，则scala将其定义成为一个private final 字段，并为它创建一个public方法number() 用以取值。如果var name: String，则定义name为private字段，并同时提供public的getter和setter方法。如果不做修饰，则设定为private的getter和setter方法。

class People{
  println("Hello")
}

当new  People时会显示输出结果：Hello

除了主构造函数，还可以通过this()副方法构造

class  People(age: Int, name: String){
    private var address: String = _
    def this(age: Int, name: String, add: String){
        this(age,name)
        address = add
    }
}

(2) 单例

单例实例对象无法初始化，所以不能给它的主构造函数传递参数

object test{
	def calSum(start_index:Int, end_index:Int, call_fun: Int => Int) = {
		var result = 0
		for (i <- start_index to end_index){
			result += call_fun(i)
		}
		result
	}
	def main(args: Array[String]){
		if (args.length > 0) {
		  for (line <- Source.fromFile(args(0)).getLines)
		    println(line.length + " " + line)
		}
		else
		Console.err.println("Please enter filename")
	}

}

（3）继承

两点需要注意a) 重写父类方法需要显示override关键字，b）只有主构造函数才能往基类构造函数中传递参数

class  People(age: Int, name: String){
    override def toString() = {
    	"age: "+age + " name: "+name
    }
}

class Man(age: Int, name: String, sex: String) extends People(age,name){
	override def toString() = {
		"age: "+age + " name: "+name + " sex: "+sex
	}
}

简单点

class  People(age: Int, name: String){
    override def toString = "age: "+age + " name: "+name

}

class Man(age: Int, name: String, sex: String) extends People(age,name){
	override def toString = "age: "+age + " name: "+name + " sex: "+sex
}