Arraylist<String> into ArrayList<string> in java

ArrayList<String> constraints_list=new ArrayList<String>();
    public void setConstraints(ArrayList<String> c)
    {
        c =开发者_如何学C constraints_list;
        constr = true;
    }

i want to make ArrayList c to be ArrayList constraint_list... how to do that?

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It's not totally clear to me what you want to do. However, object references are passed by value in Java, so setting the value of c (as in your code) won't work. The typical way to set c from an instance variable is to write a getter rather than a setter:

public ArrayList<String> getConstraints() {
  return constraints_list;
}

You can then say:

ArrayList<String> c = getConstraints();

If on the other hand, you are trying to do the opposite (set constraints_list from the passed in parameter), then your assignment is the wrong way round:

public void setConstraints(ArrayList<String> c) {
  constraints_list = c;
  constr = true;
}

You should also consider whether it's better to make a copy of the list, in which case you could do:

public void setConstraints(ArrayList<String> c) {
  constraints_list = new ArrayList<String>(c);
  constr = true;
}