On the quest for learning Spring, but need some help

[Shashank Gokhale]

Ive been following a tutorial on youtube and Im upto the point where we start using autowire.  But the program throws a nullpointerexception and the member variables dont get the proper values.  Im including the code so please let me know whats going on

This is the main program "Drawing.java"

package org.sg.firstbean;

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

public class Drawing {
	public static void main(String[] args) {
		ApplicationContext context = new ClassPathXmlApplicationContext("Spring1.xml");
                Triangle triangle = (Triangle) context.getBean("triangle");
		triangle.draw();
	}
}

My triangle classs "Triangle.java"

package org.sg.firstbean;

public class Triangle {

	private Point A,B,C;
	
	public Point getA() {
		return A;
	}
	public void setA(Point a) {
		A = a;
	}
	public Point getB() {
		return B;
	}
	public void setB(Point b) {
		B = b;
	}
	public Point getC() {
		return C;
	}
	public void setC(Point c) {
		C = c;
	}
	public void draw(){
		System.out.println("Point A is (" + getA().getX() + "," + getA().getY() + ")");
		System.out.println("Point B is (" + getB().getX() + "," + getB().getY() + ")");
		System.out.println("Point C is (" + getC().getX() + "," + getC().getY() + ")");
	}
}

The Point class "Point.java"

package org.sg.firstbean;

public class Point {
	private int x,y;

	public int getX() {
		return x;
	}

	public void setX(int x) {
		this.x = x;
	}

	public int getY() {
		return y;
	}

	public void setY(int y) {
		this.y = y;
	}
}

and finally the xml file "Spring1.xml"

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN 2.0//EN" "http://www.springframework.org/dtd/spring-beans-2.0.dtd">
                  
<beans>
	<bean id="triangle" class="org.sg.firstbean.Triangle" autowire="byName">
<!-- 	
		<property name="A" ref="A"/>
		<property name="B" ref="B"/>
		<property name="C" ref="C"/>
-->
	</bean>
	<bean id="A" class="org.sg.firstbean.Point">
		<property name="x" value="0"/>
		<property name="y" value="0"/>
	</bean>
	<bean id="B" class="org.sg.firstbean.Point">
		<property name="x" value="-20"/>
		<property name="y" value="0"/>
	</bean>
	<bean id="C" class="org.sg.firstbean.Point">
		<property name="x" value="20"/>
		<property name="y" value="0"/>
	</bean>

</beans>

If I remove the autowire tag and include the property statements, then the application works, but if add in the autowire and delete the property statements, then the application gives a null pointer exception in Triangle class at line 54 (where it is supposed to prints the coordinates of point A" and also in the Drawing class at line 11 where the draw method is called.  Whats going on, why is it not working?

[somashaker goud]

Everything looks fine with your code ,can you re-arrange your code like below and give a try

from

    <bean id="triangle" class="org.sg.firstbean.Triangle" autowire="byName">
<!--     
        <property name="A" ref="A"/>
        <property name="B" ref="B"/>
        <property name="C" ref="C"/>
-->
    </bean>

to

    <bean id="triangle" class="org.sg.firstbean.Triangle" autowire="byName"/>

[Shashank Gokhale]

I got it to work actually.  The problem was, and I dont know why, that I was naming my points A,B,C,D, and I named them as such in the xml file.  The issue was that Eclipse, when generating the getter and setter methods, especially the setter method was passing in lowercase d even though I had used D when declaring the Point D property.  And because the objects are case sensitive, I was getting the null pointer exception