@Autowired：该注解应用于有值设值方法、非设值方法、构造方法和变量。
bean文件
<?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:p="http://www.springframework.org/schema/p"
xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-4.3.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-4.3.xsd">
<context:component-scan base-package="com.lyc" />
<bean id="helloWorld" class="com.lyc.spring.HelloWorld">
<property name="name" value="Spring_HelloWorld"></property>
</bean>
<bean id="car" class="com.lyc.spring.Car"></bean>
<bean id="user" class="com.lyc.spring.User" autowire="byName"></bean>
</beans>
换句话理解是省去了get set的方法，
创建一个car
package com.lyc.spring;
public class Car {
public void start(){
System.out.println("starting car...");
}
}
创建一个User，使用autowire可以省去setcar
package com.lyc.spring;
import org.springframework.beans.factory.annotation.Autowired;
public class User {
@Autowired
private Car car;
// public void setCar(Car car) {
// this.car = car;
// }
public void startCar() {
car.start();
}
}
测试
public class Main {
public static void main(String[] args) {
ApplicationContext ctx = new ClassPathXmlApplicationContext("bean.xml");
User user = (User) ctx.getBean("user");
user.startCar();
}
}
如果把autowire去除 报错 Exception in thread "main" java.lang.NullPointerException
