java - Spring 4 @Autowire not binding correctly? -

i m trying autowire bean implementation returns null pointer exception.

package org.com.api;  public interface multiply {     public int multipler(int a, int b); }  package org.com.core; import org.com.api.multiply;  public class multiplyimpa implements multiply {     public int multipler(int a, int b){         return a*b;     } }  package org.com.core; import org.com.api.multiply; public class multiplyimpb implements multiply {     public int multipler(int a, int b){         int total = 0;         for(int = 1; <=b; i++){             total += a;         }         return total;     } }  package org.com.service; import org.com.api.multiply; public calculator {     @autowire     private multiply multiply;     public int calcmultiply(int a, int b){         return multiply.multipler(a,b);     } } 

in applicationcontext.xml have added following

<bean id="multiply" class="org.com.core.multiplyimpa" scope="prototype"/> 

now in runtime nullpointerexpection. multiply null.

for testing purpose tried this. works, understand here m explicitly getting bean. means autowire didnt work ? there m missing ?

multiply m = (multiply)factory.getbean("multiply"); system.out.println(m.multiplier(2,4); 

seems have typo in bean xml.

instead of

<bean id="multiply" class="package org.com.core.multiplyimpa" scope="prototype"/> 

it should (using full qualified classname only)

<bean id="multiply" class="org.com.core.multiplyimpa" scope="prototype"/> 

edit:

possible error calculator class not managed spring. instantiating class using new operator fail because there no way spring reference inject collaborator:

calculator calculator = new calculator(); calculator.calcmultiply(1, 2); // throw npe because `multiply` instance (in case `multiplyimpa`) has not been injected. 

so instead instantiate calculator class using spring:

<bean id="calculator" class="org.com.service.calculator"/> <bean id="multiply" class="org.com.core.multiplyimpa"/>  

retrieve through application-context:

classpathxmlapplicationcontext ctx = new classpathxmlapplicationcontext("application-context.xml"); calculator calculator = ctx.getbean(calculator.class); 

spring manage dependencies scanning @autowired annotation, looking @ field type , trying find qualified bean application context.