问题
System.arraycopy() is a shallow copy method.
For an array of a primitive type, it will copy the values from one array to another:
int[] a = new int[]{1,2};
int[] b = new int[2];
System.arraycopy(a, 0, b, 0, 2);
b will be {1,2} now. Changes in a will not affect b.
For an array of a non-primitive type, it will copy the references of the object from one array to the other:
MyObject[] a = new MyObject[] { new MyObject(1), new MyObject(2)};
MyObject[] b = new MyObject[2];
System.arraycopy(a, 0, b, 0, 2);
b will contain a reference of new MyObject(1), new MyObject(2) now. But, if there are any changes to new MyObject(1) in a, it will affect b as well.
Are the above statements correct or not?
回答1:
Above statements are correct or not?
Yes, you are correct.
System.arraycopy always does a shallow copy, no matter if the array contains references or primitives such as ints or doubless.
Changes in array a will never affect array b (unless a == b of course).
But if any changes of new MyObject(1) in
a, it will affectbas well.
Depends on what you mean. To be picky, a change to the new MyObject(1) will neither affect a nor b (since they only contain references to the object, and the reference doesn't change). The change will be visible from both a and b though, no matter which reference you use to change the object.
回答2:
You're correct as long as you're specifically modifying properties and calling methods on your objects.
If you change where the reference points, for example with a[0] = new MyObject(1), then even though the objects were created with the same initialization data, they will now point to different instances of the object and a change to one instance will not be seen in the other reference (in array b).
来源：https://stackoverflow.com/questions/6101684/does-java-lang-system-arraycopy-use-a-shallow-copy