在java中，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(Class<t>type,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, wh ich
- * 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";
- }
- }
上面的这个例子比较简单，但是如果你有接触过泛型数组，你便对他的复杂度有一定的了解，由于创建泛型数组比较复杂，所以在实际的应用过程中一般会选择List的对泛型进行存储，如果实在需要使用泛型数组，则需要注意数组的在运行时的类型，think in java这本书中，对泛型数组的处理通过四个小程序对其进行了比较完整的描述。
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;
- /*
- * will throw ClassCastException :The problem is that arrays keep track of their actual type, and that type is
- * established at the point of creation of the array. So even though genArr has been cast to a Generic < Integer
- * >[] , that information only exists at compile time (and without the @SuppressWarnings annotation, you’d get a
- * warning for that cast). At run time, it’s still an array of Object, and that causes problems.
- */
- // genArr = (Generic<Integer>[]) new Object[] {};
- /* can not create a generic of array */
- // genArr=new Generic<Integer>[2];
- 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。
- /**
- *
- * Because of erasure, the runtime type of the array can only be Object[]. If we immediately cast it to T[], then at
- * compile time the actual type of the array is lost, and the compiler may miss out on some potential error checks.
- *
- *
- *
- * archive $ProjectName: $
- *
- * @author Admin
- *
- * @version $Revision: $ $Name: $
- */
- 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
- /**
- *
- * Initially, this doesn’t look very different compare with ArrayOfGeneric2.java , just that the cast has been moved.
- * Without the ©SuppressWarnings annotations, you will still get "unchecked" warnings. However, the internal
- * representation is now Object[] rather than T[]. When get( ) is called, it casts the object to T, which is in fact the
- * correct type, so that is safe. However, if you call rep( ) , it again attempts to cast the Object[] to a T[], which
- * is still incorrect, and produces a warning at compile time and an exception at run time. Thus there’s no way to
- * subvert the type of the underlying array, which can only be Object[]. The advantage of treating array internally as
- * Object[] instead of T[] is that it’s less likely that you’ll forget the runtime type of the array and accidentally
- * introduce a bug (although the majority, and perhaps all, of such bugs would be rapidly detected at run time)
- *
- *
- *
- * archive $ProjectName: $
- *
- * @author Admin
- *
- * @version $Revision: $ $Name: $
- */
- 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***的解决方案
- /**
- *
- * The type token Class<T> is passed into the constructor in order to recover from the erasure, so that we can create
- * the actual type of array that we need, although the warning from the cast must be suppressed with @SuppressWarnings.
- * Once we do get the actual type, we can return it and get the desired results, as you see in main( ). The runtime type
- * of the array is the exact type T[].
- *
- * @author Admin
- *
- * @version $Revision: $ $Name: $
- */
- 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();
- }
- }
- }
泛型这一章节的内容从擦除开始，觉得都是非常的难懂,如果哪位同志有比较好的建议，希望能不惜指教！
原文链接：http://blog.csdn.net/sun7545526/article/details/7262486
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