将值添加到其他arraylist后，覆盖到arraylist中的旧值

Question

I'm facing the problem and I did not find for any exact explanation for it. I am running the program in debug mode, I see that when the variable add to g_temNodes arraylist: g_tempNodes.add(p_dept_cd); , that variable also automatically add to g_nodes before the running g_nodes.add(g_tempNodes); .

Pls give me some ways to solve it. Thanks in advance.

my code is as the followings.

ArrayList<ArrayList<String>> g_nodes = new ArrayList<ArrayList<String>>();
ArrayList<String> g_tempNodes = new ArrayList<String>();
...
...
private String GetDeptCd(String x_dept_cd, int x_flag) {
...
...
while (p_sql.next()) {
    String p_dept_cd = p_sql.getString("dept_cd");
    if(x_flag == 0){
        g_tempNodes.removeAll(g_tempNodes);
    }
    g_tempNodes.add(p_dept_cd);
    System.out.println("g_tempNodes = "+g_tempNodes);
    g_nodes.add(g_tempNodes);
    System.out.println("g_nodes = "+g_nodes);
    GetDeptCd(p_dept_cd, 1);
    g_tempNodes.remove(g_tempNodes.size()-1);
}
return null;
}

This is the output in console.

g_tempNodes = [100]
g_nodes = [[100]]

g_tempNodes = [100, 999]
g_nodes = [[100, 999], [100, 999]]

g_tempNodes = [100, 101]
g_nodes = [[100, 101], [100, 101], [100, 101]]

Answer 1

Since you're using the same g_tempNodes always, the values are getting overwritten. Declare a new g_tempNodes in the loop always

ArrayList<ArrayList<String>> g_nodes = new ArrayList<ArrayList<String>>();
// ArrayList<String> g_tempNodes = new ArrayList<String>(); // not needed here
...
while (p_sql.next()) {
    ArrayList<String> g_tempNodes = new ArrayList<String>(); // new list created always
    ...
}