java - 如何在java列表中使用addall

Question

您好，我必须将元素添加到我的列表中，我注意到如果我使用 add 方法，我只是将引用添加到我的列表中，但我想添加元素而不是引用:

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

您每次都添加相同的ArrayState对象。您应该每次在 while 循环中创建一个新的 ArrayState 对象，以避免每次都发生更改。这是因为默认情况下，Java 中对象始终通过引用传递。尝试这样做:

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);

}