报错：Type mismatch: cannot convert from Object to Car

问题描述：

一个非常简单的spring项目，用静态工厂方法配置bean实例。项目的目录结构如下：

代码如下：

Car.java

 package com.tt.spring.beans.factory;

 public class Car {

     private String brand;
     private double price;

     public String getBrand() {
         return brand;
     }
     public void setBrand(String brand) {
         this.brand = brand;
     }
     public double getPrice() {
         return price;
     }
     public void setPrice(double price) {
         this.price = price;
     }

     public Car(){
         System.out.println("Car's Constructor...");
     }

     public Car(String brand, double price) {
         super();
         this.brand = brand;
         this.price = price;
     }

     @Override
     public String toString() {
         return "Car [brand=" + brand + ", price=" + price + "]";
     }

 }

StaticCarFactory.java

 package com.tt.spring.beans.factory;

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

 /**
  * 静态工厂方法：直接调用某一个类的静态方法就可以返回Bean的实例
  */
 public class StaticCarFactory {

     private static Map<String,Car> cars = new HashMap<String, Car>();

     static{
         cars.put("Audi",new Car("Audi",300000));
         cars.put("Ford", new Car("Ford",40000));
     }

     //静态工厂方法
     public static Car getCar(String name){
         return cars.get(name);

     }

 }

beans-factory.xml

 <?xml version="1.0" encoding="UTF-8"?>
 <beans xmlns="http://www.springframework.org/schema/beans"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xmlns:context="http://www.springframework.org/schema/context"
     xmlns:p="http://www.springframework.org/schema/p"
     xmlns:util="http://www.springframework.org/schema/util"
     xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
         http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-4.0.xsd
         http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-4.0.xsd">

     <!-- 通过静态方法来配置bean.注意不是配置静态工厂方法实例，而是配置bean实例 -->
     <bean id="car1"
           class="com.tt.spring.beans.factory.StaticCarFactory"
           factory-method="getCar">
           <constructor-arg value="Audi"></constructor-arg>
     </bean>

 </beans>

Main.java:

 package com.tt.spring.beans.factory;

 import org.springframework.context.ApplicationContext;
 import org.springframework.context.support.ClassPathXmlApplicationContext;

 public class Main {

     public static void main(String[] args){

         ApplicationContext ctx = new ClassPathXmlApplicationContext("beans-factory.xml");

         Car car1 = (Car) ctx.getBean("car1");
         System.out.println(car1);
     }
 }

运行Main.java程序，控制台报错如下：

Exception in thread "main" java.lang.Error: Unresolved compilation problem:
Type mismatch: cannot convert from Object to Car

at com.tt.spring.beans.factory.Main.main(Main.java:12)

原因分析：

第一, 需要装 jre1.5.0及以上的版本

第二, 在eclipse的'Window' 'Preference' 'Java'里,
'Install JREs'里设置你装的jre

第三,在eclipse的'Window' 'Preference' 'Java'里,
'Compiler'里设'Compiler compliance level'为5.0以上
（关键是第三步, 兼容级别）

问题解决：

由于我安装的jdk版本是1.8.0的，所以问题应该出在Compiler compliance level上。

进入Window->Preference->Java->Compiler,发现Compiler compliance level=1.5

将Compiler compliance level改成1.8：

再运行Main.java代码，运行正常，控制台显示如下信息：