Java: How to make a copy of an array of object?

Question

Right now, I have an array of Point objects and I want to make a COPY of that array.

I have tried following ways:

1) Point[] temp = mypointarray;

2) Point[] temp = (Point[]) mypointarray.clone();

3)

Point[] temp = new Point[mypointarray.length]; System.arraycopy(mypointarray, 0, temp, 0, mypointarray.length);

But all of those ways turn out to be that only a reference of mypointarray is created for temp, not a copy.

For example, when I changed the x coordinate of mypointarray[0] to 1 (the original value is 0), the x coordinate of temp[0] is changed to 1 too (I swear I didn't touch temp).

So is there any ways to make an copy of Point array?

Thanks

what you doing i believe is shallow copy.you have option to use copy constructor.follow this thread stackoverflow.com/questions/3947227/… — Umesh Awasthi
– Umesh Awasthi, Commented Nov 20, 2011 at 6:48

Ted Hopp · Accepted Answer · 2017-11-13 21:52:21Z

You need to make a deep copy. There's no built-in utility for this, but it's easy enough. If Point has a copy constructor, you can do it like this:

Point[] temp = new Point[mypointarray.length]; for (int i = temp.length - 1; i >= 0; --i) { Point p = mypointarray[i]; if (p != null) { temp[i] = new Point(p); } }

This allows for null array elements.

With Java 8, you can do this more compactly with streams:

Point[] temp = Arrays.stream(mypointarray) .map(point -> point == null ? null : new Point(point)) .toArray(Point[]::new);

And if you're guaranteed that no element of mypointarray is null, it can be even more compact because you can eliminate the null test and use Point::new instead of writing your own lambda for map():

Point[] temp = Arrays.stream(mypointarray).map(Point::new).toArray(Point[]::new);

@aniztar -- Well, presumably the class provides some mechanism for making a copy of an instance (another constructor; a copy() method; a builder class; serialize/deserialize; clone(); something) so just use whatever's available where I was using a copy constructor. If you have no way of making a copy of an instance, then you're pretty much out of luck.

DarkSquirrel42 · Accepted Answer · 2011-11-20 06:47:28Z

you will have to create copies of all Point instances yourself ...

as long as your Point Class is serializable, you can serialize + deserialize that array to obtain a quick deep copy

If the Point class is java.awt.Point, then it does implement Serializable.

Finbarr · Accepted Answer · 2011-11-20 06:47:38Z

-4

You can use the Arrays utility class:

import java.util.Arrays; ... Point[] copy = Arrays.<Point>copyOf(mypointarray, mypointarray.length);

answered Nov 20, 2011 at 6:47

Finbarr

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dr.scre Over a year ago

Arrays.copyOf() makes a shallow copy

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