Scala Basics 12 Scala Application, factory method and Singleton mode implementation

1. Apply can be used to implement an instance of an initialization class similar to static, see the following example

Package Smart.iotclass Applyclass {  }class a{    def apply () =println ("Hello class A");} Object b{  def apply () =println ("Hello object B");} Object applyrun{  def main (args:array[string]): Unit = {         //Display call to apply Method     b.apply ()     //Direct parentheses can also call Appy method     B ();         Instantiate a Class A    var a= new A ()    //Show Call apply Method     a.apply ()     //     A ()  }}


Result
Hello Object B
Hello Object B
Hello class A
Hello class A

2. Use apply to implement the Factory method, with the Apply object static to implement other classes. If you don't understand, look at the list.

Package Smart.iotclass Applyclass {  }class a{    def Test () =println ("function test")    def apply () =println (" Hello class A ");} Object b{  def apply () =println ("Hello object B");} Similar to a factory method, use the C apply method to instantiate Aobject c{  def apply () =new A ()}object applyrun{  def main (args:array[string]): Unit = {           //similar to defining a static method initialization, using C to refer to a method   var  c=c ()   c.apply ()   c.test ()  }}

3. Use apply to achieve a singleton mode, let's do a test. Reference the associated object C with C and C1, respectively

Package Smart.iotclass Applyclass {  }class a{    def Test () =println ("function test")    def apply () =println ( "Hello class A");} Object b{  def apply () =println ("Hello object B");} Similar to a factory method, use the C apply method to instantiate Aobject c{  def apply () =new A ()}object applyrun{    var  c=c ()    println ( c.tostring)    var c1=c ()    println (c1.tostring)  }}result:[email Protected][email protected]

So what we get is actually two objects, each time C will instantiate some new a object, let's change it to a singleton mode

Package Smart.iotclass Applyclass {  }class a{    def Test () =println ("function test")    def apply () =println (" Hello class A ");} Object b{  def apply () =println ("Hello object B");} Similar to a factory method, use the C's apply method to instantiate Aobject c{  //Define an A object to give a default value  var a:a=_  //If A is implemented, new A will return a if it has already been implemented the simple interest mode  def apply () =if (a==null) {a=new a (); A}else a}object applyrun{  def main (args:array[string]): Unit = {      var< C10/>c=c ()    println (c.tostring)    var c1=c ()    println (c1.tostring)  }}result:[email protected][ Email protected]

Scala Basics 12 Scala Application, factory method and Singleton mode implementation