如何在列表java中使用addall

Question

Hello I have to add elements to my list and I notice if I Use the method add I just add the reference to my list but I would like to add the elements and not the reference:

ArrayList ArrayListIdle = new ArrayList();
List<State> arrayState = new ArrayList<State>();

while(rs.next){

state = new State();

state.updateStateArray(arrayState);//This function mods the elements of (arrayState);//This 
state.setArrayStates(arrayState);//add a list of arrayState to the object state


//I have a array and I want to add the element state with his arraylist(not the reference to)

ArrayListIdle.addAll(state);

// I tried with add , but in the next iteration the arrayState change.

}

Answer 1

The problem here is that you have one "arrayState" object and all of the state objects reference the same one.

One way to solve that here is to move the object creation inside loop so that a different object is created every time.

 while(rs.next) {
      List<State> arrayState = new ArrayList<State>();
      ...
 }

Answer 2

You are adding the same ArrayState object every time. You should create a new ArrayState object every time in the while loop to avoid it getting changed every time. This is because by default objects are always passed by reference in Java. Try doing this:

ArrayList arrayListIdle = new ArrayList();


while(rs.next){

    state = new State();
    List<State> arrayState = new ArrayList<State>();

    state.updateStateArray(arrayState);//This function mods the elements of (arrayState);//This 
    state.setArrayStates(arrayState);//add a list of arrayState to the object state
    arrayListIdle.addAll(state);

}