Different types of dependency injection(DI)

There are two types of dependency injection: setter injection and constructor injection.

Setter Injection: Normally in all the java beans, we will use setter and getter method to set and get the value of property as follows:

public class namebean {
String name;
public void setName(String a) {
name = a; }
public String getName() {
return name; }
}

We will create an instance of the bean 'namebean' (say bean1) and set property as bean1.setName("tom"); Here in setter injection, we will set the property 'name' in spring configuration file as showm below:
<bean id="bean1" class="namebean">
<property name="name" >
<value>tom</value>
</property>
</bean>
The subelement <value> sets the 'name' property by calling the set method as setName("tom"); This process is called setter injection.
To set properties that reference other beans <ref>, subelement of <property> is used as shown below,
<bean id="bean1" class="bean1impl">
<property name="game">
<ref bean="bean2"/>
</property>
</bean>
<bean id="bean2" class="bean2impl" />


Constructor injection: For constructor injection, we use constructor with parameters as shown below,

public class namebean {
String name;
public namebean(String a) {
name = a;
}
}

We will set the property 'name' while creating an instance of the bean 'namebean' as namebean bean1 = new namebean("tom");

Here we use the <constructor-arg> element to set the the property by constructor injection as
<bean id="bean1" class="namebean">
<constructor-arg>
<value>My Bean Value</value>
</constructor-arg>
</bean>

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