Processing.org-按值传递对象

Question

I am pretty new to this language. I have an object and I want to pass it by value to another method:

// Drawings
class Drawings
{
   // Has some variables

   Drawings()
   {

   }

   // Hass some methods

} 

class History
{
    ArrayList<Drawings> prevDrawings;

    History()
    { 
        this.prevDrawings = new ArrayList<Drawings>();
    }

    void add(Drawings newDrawing) {}

}

Now, say I have a Drawings myDrawing and History myHistory , and I want to pass myDrawing by value to myHistory . The following way passes it by reference:

myHistory.add(myDrawing);

How can I then pass this by value?

Answer 1

Everything in Java, and therefore Processing, is already pass-by-value. Nothing is passed by reference.

If that doesn't make sense, read this and then read this .

What you might mean is that you want to pass a copy of the Object into a method. There are multiple ways to do that. Let's say you have this as your Object:

class MyObject{
   String thing1;
   double thing2;
   int thing3;
}

You could create a copy method outside of the MyObject class:

public MyObject copy(MyObject original){
   MyObject copy = new MyObject();
   copy.thing1 = original.thing1;
   copy.thing2 = original.thing2;
   copy.thing3 = original.thing3;
}

You could create a copy method inside the MyObject class:

class MyObject{
   String thing1;
   double thing2;
   int thing3;

   public MyObject copy(){
      MyObject copy = new MyObject();
      copy.thing1 = this.thing1;
      copy.thing2 = this.thing2;
      copy.thing3 = this.thing3;
   }

}

Or you could create a copy constructor:

class MyObject{
   String thing1;
   double thing2;
   int thing3;

   public MyObject(MyObject copy){
      this.thing1 = copy.thing1;
      this.thing2 = copy.thing2;
      this.thing3 = copy.thing3;
   }
}

You could also use serialization, but that goes a little outside normal Processing.