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I have two questions:

  1. If I have the following code:

    private boolean handleCollision(Rectangle_Double test)
{
    Rectangle_Double s = test;
    s.setLocation(s.X+xVelocity, s.Y);
}

am I modifying the passed in Rectangle_Double? If so, what would be the best way to copy the passed in Rectangle_Double and modify it?

Second, If I were to code this in python like so:

def handleCollision(collidedLands, testRectangle)
    s = testRectangle
    s.setLocation(s.X+xVelocity, s.Y)

am I modifying the passed in testRectangle? If so, what would be the best way to copy the passed in testRectangle and modify it?

Thanks!

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1  
In the Java example, you are modifying test. Unfortunately I don't know enough about Python to help you in the second example. – Vulcan Nov 6 '12 at 6:34
Thanks for answering the java portion :) – user1170679 Nov 6 '12 at 6:46
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2 Answers

up vote 2 down vote accepted

I don't speak Java, but to answer the Python questions:

  1. Yes, you are modifying testRectangle.

  2. If you wish not to modify it, make a new rectangle and return that.

Something like this, assuming you have a constructor for rectangles:

def handleCollision(collidedLands, testRectangle):
    newRectangle = Rectangle(testRectangle.X + xVelocity, testRectangle.Y)
    return newRectangle
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Awesome thanks! – user1170679 Nov 6 '12 at 6:46
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up vote 2 down vote

Both Python and Java have only pass by value. Every value in Python is a reference, just like in Java every non-primitive value is a reference. Objects are not values in either language. Their semantics for passing and references are pretty much identical, whatever name you choose to call them by.

Therefore, your Java code:

private void handleCollision(Rectangle_Double test)
{
    Rectangle_Double s = test;
    s.setLocation(s.X+xVelocity, s.Y);
}

is identical to the equivalent Python code:

def handleCollision(self, test):
    s = test
    s.setLocation(s.X+xVelocity, s.Y)

As I said before, objects are not values in either language. The values that are passed in both cases are references (pointers to objects). All objects in Python and Java must be manipulated through references. Like all types, references are passed by value.

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