Constructor injection in spring & ambiguity

Summary

• Notice the output of the code: `

  instance of useStudent created using str-constructor
  Student name: 101
  Student roll: 0
  

`

• We can see the value of name is 101 and roll is 0.
• Why roll is 0 ?
  • The roll is 0 since the construction injection is done for roll no, and we all know the Java sets the default value of local data member. Here, i.e. roll is of type int, therefore the value 0 is assigned.
• Why name is 101 ?
  • That’s because the Spring container prefers String parameter over others because by default every value is convertible to String.
  • So Spring assumes that we want to call the String argument constructor with the value "101".
• The solution is to use type attribute inside <constructor-arg/> whose value will be data type.

Syntax

`

    <bean class="com.constructor.injection.beans.Student" id="useStudent">
        <constructor-arg value="101" />
    </bean>

`

Note

• Always remember, this punchline SPRING LOVES SPRING, it will always give preference to String data type.
• The Spring data type is considered primitive inside Spring.