Integer is a subtype of Number
Double is a subtype of Number
ArrayList<E> is a subtype of List<E>
List<E> is a subtype of Collection<E>
Collection<E> is a subtype of Iterable<E>
public class ArrayList<E> extends AbstractList<E>
implements List<E>, RandomAccess, Cloneable, java.io.Serializable
public static void main(String args[]) {
List<Number> nums = new ArrayList<Number>();
List<Integer> ints = Arrays.asList(, );
List<Double> dbls = Arrays.asList(2.78, 3.14);
nums.addAll(ints);
nums.addAll(dbls);
for(Number d: nums)
System.out.println(d);
}
package cn.galc.test; import java.util.*; class Collections{
public static <T> List<T> toList(T[] arr)
{
List<T> list = new ArrayList<T>();
for (T t: arr)
{
list.add(t);
}
return list;
} public static <T> void copy(List<? super T> dst, List<? extends T> src) {
for (int i = ; i < src.size(); i++) {
dst.set(i, src.get(i));
}
}
} public class Test {
public static void main(String args[]) {
List<Object> objs = Arrays.<Object>asList(, 3.14, "four");
List<Integer> ints = Arrays.asList(, );
Collections.copy(objs, ints);
for(Object o: objs)
System.out.println(o);
}
}