Question:

I don't have a better title for this question, you may help me change it.

class Example { class A { private String str; public String getStr() { return str==null ? "nothing" : str; } public void setStr(String str) { this.str = str; } } public static void main(String[] args) { A a = null; loadA(a); System.out.println(a.getStr()); } private static void loadA(A a) { // a = ****; // in my project, a is load from a json string using Gson // Gson cannot modify a Object, it can only create a new one, say b // I tried to copy every field from b to a // but the method getStr do not always return the true str // so I may have to create another method "getTrueStr()" which feels bad } }

Considered solutions and problems:

<ol><li>a = Gson.createAnotherA()</li> </ol>

It doesn't work.

<ol><li>I tried to copy every field from b to a</li> </ol>

but the method getStr() do not always return the true str, so I may have to create another method getTrueStr() which make me feel bad.

<ol start="2"><li>clone()</li> </ol>

make me feel even worse.

<ol start="3"><li>a = loadA(a);</li> </ol>

this one is good. But I don't very like it. Because I have other loadB(), loadC() and they don't need this syntax, and it will look just inharmonious. If no better solution comes up, I'd choose this one.

Question is, what can I do if I choose none of my given solution.

or

If I am given a reference A a in a method, how can I make it the same to another Object while not using clone() and what I wrote above.

I think your problem really lies in your getStr method, which is not a real getter, it contains some logic. Is it possible to handle this outside class A?

As far as I understand, you want to create object b (of type A), which is copy of existing instance a.

Because a is loaded from JSON, you could just read the JSON again, which should create a new instance. I guess for some reason you cannot do this.

Instead of using JSON serializer or clone method (which shouldn't be used at all - it has multiple flaws), you could create a "copy-constructor":

class A { private String str; public A() {} public A(A that) { this.str = that.str; } public String getStr() { return str==null ? "nothing" : str; } public void setStr(String str) { this.str = str; } }

I came out with this. Perfectly satisfied my need and looks nice.

class A {

private A reference; private String name; public A() { reference = this; } public void setReference(A ref) { reference = ref; } public void setName(String name) { reference.name = name; } public String getName() { return reference.name; } }