Spring Autowiring only works with Interface

I am quite new to spring framework and came across the following issue.

I have an interface ClassA, which is implemented by classed ClassA1 and ClassA2.

I have the following bean definition added to applicationContext.xml

<bean id="class1" class="com.abc.ClassA1" />
<bean id="class2" class="com.abc.ClassA2" />

I would like to Autowire both the implementation classes as below.

@Autowired
private ClassA1 classA1;

@Autowired
private ClassA2 classA2;

The above code is throwing error as

Could not autowrite to field: com.abc.ClassA1 com.abc.SomeClass.classA1; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No matching bean of type [com.abc.ClassA1]

But, if I change the autowiring to interface as below:

@Autowired
ClassA classA1;

Then ClassA1 is autowired to the variable. I am clueless on how can I autowire a variable to ClassA2.