Inheritance in Spring

[Schandha Ravi]

Please see the below code,

I have two classes Person and Student, such a way that Student extends Person.

Person class

    

package com.beans;

public class Person {
	protected String id=null;
	protected String name=null;
	
	public Person(){
		System.out.println("In Person constructor");
	}
	public String getId(){
		return id;
	}
	public String getName(){
		return name;
	}
	public void setId(String id){
		this.id=id;
	}
	public void setName(String name){
		this.name=name;
	}
}

Student class

    

package com.beans;

public class Student extends Person{
	protected String clazz=null;
	public Student(){
		System.out.println("In Student constructor");
	}
	public void setClazz(String clazz){
		this.clazz=clazz;
	}
	public String getClazz(){
		return clazz;
	}
}

and my configuration file is as follows

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN"
"http://www.springframework.org/dtd/spring-beans.dtd">
<beans>
	<bean id="Person" class="com.beans.Person">
		<property name="id">
			<value>123</value>
		</property>
		<property name="name">
			<value>abc xyz</value>
		</property>
	</bean>
	<bean id="Student" class="com.beans.Student">
		<property name="clazz">
			<value>Fifth</value> 
		</property>
	</bean>
</beans>
    

and now through my client, I'm expecting to instantiate Student bean through IoC and need to display the id, name and class. But unfortunately, I'm able to display only the class name.

    
package com.client;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.xml.XmlBeanFactory;
import org.springframework.core.io.*;
import java.io.*;
import com.beans.*;

public class StandaloneClient {
	public static void main(String[] args)throws Exception{
		BeanFactory factory=new XmlBeanFactory(new FileSystemResource(new File("beans.xml")));
		Student s=(Student)factory.getBean("Student");
		
		System.out.println("Student id is : "+s.getId());
		System.out.println("Student name is : "+s.getName());
		System.out.println("Student class is : "+s.getClazz());
	}
}

From the output, I observe that the constructor of Person is invoked when IoC instantiates Student as expected. But when I try displaying the ID and Name, they are displayed as null. Doesn't Spring container assign the values for parent object, before setting them to child object.

   
Feb 27, 2010 11:17:14 PM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
INFO: Loading XML bean definitions from file [C:\Workspace_Personal\SpringTut\beans.xml]
In Person constructor
In Student constructor
Student id is : null
Student name is : null
Student class is : Fifth

[Vijitha Kumara]

Schandha Ravi wrote:From the output, I observe that the constructor of Person is invoked when IoC instantiates Student as expected. But when I try displaying the ID and Name, they are displayed as null. Doesn't Spring container assign the values for parent object, before setting them to child object.

Spring doesn't know anything unless you tell it. That is those are just two beans spring instantiates. I haven't tried it but check this

[Schandha Ravi]

Thank you Vijitha Kumara.

[Tomas Bilek]

You must fill attribute "parent". So for example parent="Person".

Good Luck !