标签：
在java中，可以声明一个泛型数组，不能通过直接通过T[] tarr=new T[10]的方式来创建数组，最简单的方式便是通过Array.newInstance(Classtype,int size)的方式来创建数组例如下面的程序。
public class ArrayMaker<T> {
private Class<T> type;
public ArrayMaker(Class<T> type) {
this.type = type;
}
@SuppressWarnings("unchecked")
T[] createArray(int size) {
return (T[]) Array.newInstance(type, size);
}
List<T> createList() {
return new ArrayList<T>();
}
/** * @param args */
public static void main(String[] args) {
/** Even though kind is stored as Class<T> , erasure means that it is actually just being stored as a Class, with
* no parameter. So, when you do some thing with it, as in creating an array, Array.newInstance( ) doesn’t
* actually have the type information that’s implied in kind; so it cannot produce the specific result, which
* must therefore be cast, which produces a warning that you cannot satisfy.
*/
ArrayMaker<Type> am2 = new ArrayMaker<Type>(Type.class);
System.out.println(Arrays.asList(am2.createArray(10)));
System.out.println(Arrays.asList(am2.createList()));
}
}
class Type {
@Override
public String toString() {
return "type";
}
}
程序一：这个程序主要说明了，在使用泛型数组中容易出现的问题，由于书中对于程序的说明比较详细，所以只对程序做引用。
class Generic<T> {
}
public class ArrayofGeneric {
public static void main(String[] args) {
Generic<Integer>[] genArr;
genArr = (Generic<Integer>[]) new Generic[2];
System.out.println(genArr);
}
}
程序二：这个程序主要是说明在程序的执行过程中，泛型数组的类型信息会被擦除，且在运行的过程中数组的类型有且仅有Object[]，如果我们强制转换成T[]类型的话，虽然在编译的时候不会有异常产生，但是运行时会有ClassCastException抛出。
public class ArrayOfGeneric2<T> { public T[] ts; public ArrayOfGeneric2(int size) { ts = (T[]) new Object[size]; } public T get(int index) { return ts[index]; } public T[] rep() { return ts; } public void set(int index, T t) { ts[index] = t; } public static void main(String[] args) {
ArrayOfGeneric2<String> aog2 = new ArrayOfGeneric2<String>(10); Object[] objs = aog2.rep(); System.out.println(objs); /* will throw ClassCastException */ // String[] strs = aog2.rep(); //System.out.println(strs); } }
程序三：主要说明在对象中通过用Object[]来保存数据，则生成对象是，可以对其持有的对象在T和object之间进行转换，但是当设计到数组的转换时，还是会报ClassCastException
public class ArrayOfGeneric3<T> { Object[] ts; public ArrayOfGeneric3(int size) { ts = new Object[size]; } public T get(int index) { return (T) ts[index]; } public T[] rep() { return (T[]) ts; } public void set(int index, T t) { ts[index] = t; } public static void main(String[] args) {
ArrayOfGeneric3<Integer> aog2 = new ArrayOfGeneric3<Integer>(10); Object[] objs = aog2.rep(); for (int i = 0; i < 10; i++) { aog2.set(i, i); System.out.println(aog2.get(i)); } Integer[] strs = aog2.rep(); System.out.println(strs); } }
程序四：是对泛型数组相对而言比较完美的解决方案
public class ArrayOfGeneric4<T> { T[] ts; public ArrayOfGeneric4(Class<T> type, int size) { /* to solution array of generic key code! */ ts = (T[]) Array.newInstance(type, size); } public T get(int index) { return ts[index]; } public T[] rep() { return ts; } public void set(int index, T t) { ts[index] = t; } public static void main(String[] args) {
ArrayOfGeneric4<Integer> aog2 = new ArrayOfGeneric4<Integer>(Integer.class, 10); Object[] objs = aog2.rep(); for (int i = 0; i < 10; i++) { aog2.set(i, i); System.out.println(aog2.get(i)); } try { Integer[] strs = aog2.rep(); System.out.println("user Array.newInstance to create generci of array was successful!!!!! "); } catch (Exception ex) { ex.printStackTrace(); } } }
原文请见http://developer.51cto.com/art/201202/317813.htm
标签：
原文地址：http://www.cnblogs.com/onlysun/p/4531604.html
