Java泛型實例化

泛型對象可以實例化嗎？

不可以，T t=new T()是不可以的，編譯器會報錯。由於泛型擦除，編譯器在編譯時無法確定泛型所對應的真實類型

 

解決方法

使用反射新建實例

Type superclass = getClass().getGenericSuperclass(); ParameterizedType parameterizedType = null; if (superclass instanceof ParameterizedType) { parameterizedType = (ParameterizedType) superclass; Type[] typeArray = parameterizedType.getActualTypeArguments(); if (typeArray != null && typeArray.length > 0) { clazz = (Class<T>) typeArray[0];  } }

 

執行結果

控制台輸出

 

完整代碼

package com.learn.genericinstance; import java.lang.reflect.ParameterizedType; import java.lang.reflect.Type; public class GenericInstanceLearn { public static void main(String[] args) throws InstantiationException, IllegalAccessException { UserDao userDao = new UserDao(); System.out.println(userDao.toString()); } } class Dao<T> { public Class<T> clazz; public T user; public Dao() throws IllegalAccessException, InstantiationException { Type superclass = getClass().getGenericSuperclass(); ParameterizedType parameterizedType = null; if (superclass instanceof ParameterizedType) { parameterizedType = (ParameterizedType) superclass; Type[] typeArray = parameterizedType.getActualTypeArguments(); if (typeArray != null && typeArray.length > 0) { clazz = (Class<T>) typeArray[0]; user= clazz.newInstance(); } } } @Override public String toString() { return "Dao{" + "user=" + user.toString() + '}'; } } class UserDao extends Dao<User> { public UserDao() throws IllegalAccessException, InstantiationException { } @Override public String toString() { return super.toString(); } } class User { String name; public User() { this.name = "default name"; } @Override public String toString() { return "User{" + "name='" + name + '\'' + '}'; } }