java中指定删除list对应元素

public static void rmListtest(){
String str[] = {"1","2","3","4","5","6","7","8"};
List<String> list = new ArrayList<String>();
for(int i=0; i<str.length; i++){
list.add(str[i]);
}
System.out.println(list);
int[] pos = {2,3,5,6,7};
for(int j=pos.length-1; j>=0; j--){
list.remove(pos[j]);
System.out.println(list);
}
System.out.println("=========================");
list = new ArrayList<String>();
for(int i=0; i<str.length; i++){
list.add(str[i]);
}
System.out.println(list);
for(int j=0; j<pos.length; j++){
list.set(pos[j],null);
System.out.println(list);
}
}

[1, 2, 3, 4, 5, 6, 7, 8]
[1, 2, 3, 4, 5, 6, 7]
[1, 2, 3, 4, 5, 6]
[1, 2, 3, 4, 5]
[1, 2, 3, 5]
[1, 2, 5]
=========================
[1, 2, 3, 4, 5, 6, 7, 8]
[1, 2, null, 4, 5, 6, 7, 8]
[1, 2, null, null, 5, 6, 7, 8]
[1, 2, null, null, 5, null, 7, 8]
[1, 2, null, null, 5, null, null, 8]
[1, 2, null, null, 5, null, null, null]