Java获得泛型类型

/*
 * Copyright 2010 Sandy Zhang
 * 
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy of
 * the License at
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */

/**
 * 
 */
package org.javazone.jroi.test.reflect;

import java.lang.reflect.Field;
import java.util.HashMap;
import java.util.Map;

/**
 * @author Sandy Zhang
 */
public class Bean
{
	public Map<String, ListBean> list = new HashMap<String, ListBean>();

	public static void main(String[] args) throws SecurityException, NoSuchFieldException, IllegalArgumentException, IllegalAccessException
	{
		Field c = Bean.class.getField("list");
		Field f = Field.class.getDeclaredField("signature");
		f.setAccessible(true);
		System.out.println(((String) f.get(c)));

	}
}

Ljava/util/Map<Ljava/lang/String;Lorg/javazone/jroi/test/reflect/ListBean;>;

Field c = Bean.class.getField("list");
System.out.println(c.toGenericString());

public java.util.Map<java.lang.String, org.javazone.jroi.test.reflect.ListBean> org.javazone.jroi.test.reflect.Bean.list

package org.javazone.jroi.test.reflect;

import java.util.HashMap;
import java.util.Map;

/**
 * @author Sandy Zhang
 */
public class Bean
{
	public Map<String, ListBean> list = new HashMap<String, ListBean>();

	public Map<String, ListBean> getList()
	{
		return list;
	}

	public static void main(String[] args) throws SecurityException, NoSuchFieldException, IllegalArgumentException, IllegalAccessException, NoSuchMethodException
	{
		System.out.println(Bean.class.getMethod("getList").toGenericString());
	}
}

public java.util.Map<java.lang.String, org.javazone.jroi.test.reflect.ListBean> org.javazone.jroi.test.reflect.Bean.getList()

getGenericType
public Type getGenericType()返回一个 Type 对象，它表示此 Field 对象所表示字段的声明类型。 
如果 Type 是一个参数化类型，则返回的 Type 对象必须准确地反映源代码中使用的实际类型参数。 
如果底层字段的类型是一个类型变量或者是一个参数化类型，则创建它。否则将解析它。 
返回：
返回表示此 Field 对象所表示字段的声明类型的 Type 对象 
抛出： 
GenericSignatureFormatError - 如果一般字段签名不符合 Java Virtual Machine Specification, 3rd edition 中指定的格式 
TypeNotPresentException - 如果底层字段的一般类型签名引用了不存在的类型声明 
MalformedParameterizedTypeException - 如果底层字段的一般签名引用了一个因某种原因而无法实例化的参数化类型
从以下版本开始： 
1.5 

public class GenericTest
{
	public List<String> list = new LinkedList<String>();

	public static void main(String[] args) throws SecurityException, NoSuchFieldException
	{
		ParameterizedType pt = (ParameterizedType) GenericTest.class.getField(
				"list").getGenericType();
		System.out.println(pt.getActualTypeArguments().length);
		System.out.println(pt.getActualTypeArguments()[0]);
	}
}

import java.util.List;
import java.util.Map;

public class GenericClass<T> {                // 1
    private List<T> list;                     // 2
    private Map<String, T> map;               // 3
    
    public <U> U genericMethod(Map<T, U> m) { // 4
        return null;
    }
}

private java.util.Map map;
  Signature: Ljava/util/Map;
  Signature: length = 0x2
   00 0A

const #10 = Asciz       Ljava/util/Map<Ljava/lang/String;TT;>;;

public class GenericClass extends java.lang.Object
  Signature: length = 0x2
   00 12
// ...
const #18 = Asciz       <T:Ljava/lang/Object;>Ljava/lang/Object;;

import java.util.ArrayList;
import java.util.List;

public class TestClass {
    public static void main(String[] args) {
        List<String> list = null;       // 1
        list = new ArrayList<String>(); // 2
        for (int i = 0; i < 10; i++) ;
    }
}

StackMapTable: number_of_entries = 2
 frame_type = 253 /* append */
   offset_delta = 12
   locals = [ class java/util/List, int ]
 frame_type = 250 /* chop */
   offset_delta = 11

static List<Object> list = new ArrayList<Object>();

public static void main(String[] args)
{
    list.add("asasdasd");
    list.add(123);
}

static List<Object> list = new ArrayList<Object>();

public static void main(String[] args)
{
    list.add("asasdasd");
    list.add(123);
}

List<Exception> exceptions = new ArrayList<Exception>();
List<Error> errors = exceptions;

不兼容的类型
找到： java.util.List<java.lang.Exception>
需要： java.util.List<java.lang.Error>
        List<Error> errors = exceptions;
                             ^

List<Exception> exceptions = new ArrayList<Exception>();
List<Error> errors = (List) exceptions;

vector<string> vec;

int main(int argc, char* argv[]) {
    vec.push_back("abcd"); // ok
    vec.push_back(123);    // compilation error
}

template < class T, class Allocator = allocator<T> >
class vector;

#include <vector>
using namespace std;

typedef long long int64;

int main(int argc, char* argv[]) {
    vector<double> ds;
    vector<int64>* ls = &ds;
}

#include <vector>
using namespace std;

typedef long long int64;

int main(int argc, char* argv[]) {
    vector<double> ds;
    vector<int64>* ls = reinterpret_cast<vector<int64>*>(&ds);
}

using System.Collections.Generic;

static class Program {
    static void Main(string[] args) {
        IList<string> list = new List<string>();
        list.Add("abc"); // ok
        list.Add(123);   // compilation error
    }
}

IEnumerable<Apple> apples = GetApples();
IEnumerable<Fruit> fruits = apples;

using System.Collections.Generic;

static class Program {
    static void Main(string[] args) {
        IList<object> list = new List<object>();
        list.Add("abc"); // ok
        list.Add(123);   // ok, int boxed
    }
}