大虾们下面ArrayList 没有用泛型 for 循环编译错误,求原因,为什么必须的用泛型,急急急
public static void main(String args[]) {
Data data = new Data();
ArrayList list = new ArrayList(); for (int i = 100; i < 103; i++) {
data.val = i;
list.add(data);
} for (Data d : list) {
System.out.println(d.val);
}
}泛型ArrayList
public static void main(String args[]) {
Data data = new Data();
ArrayList list = new ArrayList(); for (int i = 100; i < 103; i++) {
data.val = i;
list.add(data);
} for (Data d : list) {
System.out.println(d.val);
}
}泛型ArrayList
for (Object o : list) {
Date d = (Date)o;
System.out.println(d.val);
}
for (Data d : list) {
这个里面默认了父类转子类,当然是不行。你可以这么写
for (Param d : (ArrayList<Param>)list) {