q**q
发帖数: 266 | 1 careercup上有这样一道题：implement a singleton design pattern as a template
such that for any given class Foo, you can call Singleton::instance() and
get a pointer to an instance of a singleton of type Foo
答案是用c++给出的。我用java写出下面的代码，但显然不对，请问上面的问题应该怎
么用java实现呢？
另外对下面不对的代码我也有一些疑问：
public class SingleTon {
private static T t; //报语法错误“annot make a static reference to the
non-static type T”，请问这是什么缘故？
public synchronized static T instance() {
if( t == null ) {
t = new T();//即使t非static,此处也无法instantiate,我想是因为很多
class没有default constructor的原因，这样理解是否对？
}
return t;
}
}
谢谢！ |
g*****g
发帖数: 34805 | 2 Since Java uses type erasure, generics is a compile time trick.
If it can't decide the type in compile time, it can't do instantiation.
template
the
【在 q**q 的大作中提到】
: careercup上有这样一道题：implement a singleton design pattern as a template
: such that for any given class Foo, you can call Singleton::instance() and
: get a pointer to an instance of a singleton of type Foo
: 答案是用c++给出的。我用java写出下面的代码，但显然不对，请问上面的问题应该怎
: 么用java实现呢？
: 另外对下面不对的代码我也有一些疑问：
: public class SingleTon {
: private static T t; //报语法错误“annot make a static reference to the
: non-static type T”，请问这是什么缘故？
: public synchronized static T instance() {
|
q**q
发帖数: 266 | 3 明白。那么对于上面描述的问题，能用java实现吗？
【在 g*****g 的大作中提到】
: Since Java uses type erasure, generics is a compile time trick.
: If it can't decide the type in compile time, it can't do instantiation.
:
: template
: the
|
m****r
发帖数: 6639 | 4 since you need to return any class, what you need is a map from Class to
Object.
private static Map, or Map, i am not sure.
and use reflection to instantiate the object.
template
the
【在 q**q 的大作中提到】
: careercup上有这样一道题：implement a singleton design pattern as a template
: such that for any given class Foo, you can call Singleton::instance() and
: get a pointer to an instance of a singleton of type Foo
: 答案是用c++给出的。我用java写出下面的代码，但显然不对，请问上面的问题应该怎
: 么用java实现呢？
: 另外对下面不对的代码我也有一些疑问：
: public class SingleTon {
: private static T t; //报语法错误“annot make a static reference to the
: non-static type T”，请问这是什么缘故？
: public synchronized static T instance() {
|
r*****l
发帖数: 2859 | 5 public class Singleton {
private static final Map, Object> map = new HashMap,
Object>();
public synchronized static T instance(Class c)
throws InstantiationException, IllegalAccessException {
if (!map.containsKey(c)) {
T o = c.newInstance();
map.put(c, o);
}
return (T) map.get(c);
}
}
template
the
【在 q**q 的大作中提到】
: careercup上有这样一道题：implement a singleton design pattern as a template
: such that for any given class Foo, you can call Singleton::instance() and
: get a pointer to an instance of a singleton of type Foo
: 答案是用c++给出的。我用java写出下面的代码，但显然不对，请问上面的问题应该怎
: 么用java实现呢？
: 另外对下面不对的代码我也有一些疑问：
: public class SingleTon {
: private static T t; //报语法错误“annot make a static reference to the
: non-static type T”，请问这是什么缘故？
: public synchronized static T instance() {
|
q**q
发帖数: 266 | 6 Thank you! I got it.
【在 r*****l 的大作中提到】
: public class Singleton {
: private static final Map, Object> map = new HashMap,
: Object>();
: public synchronized static T instance(Class c)
: throws InstantiationException, IllegalAccessException {
: if (!map.containsKey(c)) {
: T o = c.newInstance();
: map.put(c, o);
: }
: return (T) map.get(c);
|
q**q
发帖数: 266 | 7 Thank you!
【在 m****r 的大作中提到】
: since you need to return any class, what you need is a map from Class to
: Object.
: private static Map, or Map, i am not sure.
: and use reflection to instantiate the object.
:
: template
: the
|
r*****l
发帖数: 2859 | 8 懒惰，只给说明，不写code。
【在 m****r 的大作中提到】
: since you need to return any class, what you need is a map from Class to
: Object.
: private static Map, or Map, i am not sure.
: and use reflection to instantiate the object.
:
: template
: the
|
m****r
发帖数: 6639 | 9 我刚起床. 还不在状态.
【在 r*****l 的大作中提到】
: 懒惰，只给说明，不写code。
|
S****h
发帖数: 115 | 10 赞~
【在 r*****l 的大作中提到】
: public class Singleton {
: private static final Map, Object> map = new HashMap,
: Object>();
: public synchronized static T instance(Class c)
: throws InstantiationException, IllegalAccessException {
: if (!map.containsKey(c)) {
: T o = c.newInstance();
: map.put(c, o);
: }
: return (T) map.get(c);
|
