{"id":3941,"date":"2020-07-07T16:22:44","date_gmt":"2020-07-07T10:52:44","guid":{"rendered":"https:\/\/www.h2kinfosys.com\/blog\/?p=3941"},"modified":"2025-12-15T05:26:42","modified_gmt":"2025-12-15T10:26:42","slug":"what-is-dependency-injection","status":"publish","type":"post","link":"https:\/\/www.h2kinfosys.com\/blog\/what-is-dependency-injection\/","title":{"rendered":"What is Dependency Injection?"},"content":{"rendered":"\n

Dependency Injection is a pattern that is used to remove dependency from the programming code so that it becomes easy to manage and test the application.<\/p>\n\n\n\n

Dependency Lookup (DL): <\/strong><\/h2>\n\n\n\n

It is an approach where you get the resources after demand. There are various methods to get resources.<\/p>\n\n\n\n

  1. To get the resource directly by calling a new keyword.<\/li><\/ol>\n\n\n\n

     Example: <\/p>\n\n\n\n

    A obj = new AImpl();<\/p>\n\n\n\n

    1. Factory Method: By calling a static factory method.<\/li><\/ol>\n\n\n\n

      Example:<\/p>\n\n\n\n

      A obj = A.getA();  <\/p>\n\n\n\n

      1. Java Directory Naming Interface (JNDI): <\/li><\/ol>\n\n\n\n

        Example: <\/p>\n\n\n\n

        Context ctx = new InitialContext();  <\/p>\n\n\n\n

        Context environmentCtx = (Context) ctx.lookup(“java:comp\/env”);  <\/p>\n\n\n\n

        A obj = (A)environmentCtx.lookup(“A”);  <\/p>\n\n\n\n

        Problems in Dependency Lookup:<\/strong><\/h2>\n\n\n\n

        There are two main problems in this approach:<\/p>\n\n\n\n

        1. Tight coupling: If a resource is changed, a lot of modification is required in the programming code.<\/li>
        2. Not easy for testing: It creates a lot of problems while testing mainly in black-box testing.<\/li><\/ol>\n\n\n\n

          Dependency Injections makes the code loosely coupled and easy for testing. An example is given below:<\/p>\n\n\n\n

          class Employee{  \nAddress address;  \nEmployee(Address address){  \nthis.address=address;  \n}  \npublic void setAddress(Address address){  \nthis.address=address;  \n} \n}\n<\/pre>\n\n\n\n
          There are two ways to perform dependency injection:<\/p>\n\n\n\n
          1. By using Constructor<\/li>
          2. By using the Setter method<\/li><\/ol>\n\n\n\n
            Dependency Injection using Constructor: <\/strong><\/h2>\n\n\n\n
            Here, the dependency can be injected using constructor and is done through the bean configuration file. The properties to be set are defined under <constructor-arg> tag in the bean configuration file.<\/p>\n\n\n\n
            Example:<\/strong><\/p>\n\n\n\n
            Step 1: Book.java<\/p>\n\n\n\n
            public class Book {  \n    private int id;  \n    private String bookName;  \n    public Book() {System.out.println(\"Java\");}  \n    public Book(int id) {this.id = id;}  \n    public Book(String bookName) {  this.bookName = bookName;}  \n    public Book(int id, String bookName) {  \n        this.id = id;  \n        this.bookName = bookName;  \n    }  \n    void display(){  \n        System.out.println(id+\" \"+bookName);  \n    }  \n}\n<\/pre>\n\n\n\n
            Step 2: applicationContext.java<\/p>\n\n\n\n
            <?xml version=\"1.0\" encoding=\"UTF-8\"?>  \n<beans  \n    xmlns=\"https:\/\/www.springframework.org\/schema\/beans\"  \n    xmlns:xsi=\"https:\/\/www.w3.org\/2001\/XMLSchema-instance\"  \n    xmlns:p=\"https:\/\/www.springframework.org\/schema\/p\"  \n    xsi:schemaLocation=\"https:\/\/www.springframework.org\/schema\/beans  \n                https:\/\/www.springframework.org\/schema\/beans\/spring-beans-3.0.xsd\">  \n<bean id=\"book\" class=\"com.spring.example.Book\">  \n<constructor-arg value=\"1\" type=\"int\"><\/constructor-arg>  \n<\/bean>  \n<\/beans>\n<\/pre>\n\n\n\n
            Step 3: Main.java<\/p>\n\n\n\n
            import org.springframework.beans.factory.BeanFactory;  \nimport org.springframework.beans.factory.xml.XmlBeanFactory;  \nimport org.springframework.core.io.*;  \npublic class Main {  \n    public static void main(String[] args) {  \n        Resource r=new ClassPathResource(\"applicationContext.xml\");  \n        BeanFactory factory=new XmlBeanFactory(r);  \n        Book b=(Book)factory.getBean(\"book\");  \n        b.display();  \n    }  \n}\n<\/pre>\n\n\n\n
            Dependency Injection Using Setter Method: <\/strong><\/h2>\n\n\n\n
            Here, the dependency can be injected using setter\/getter methods and is done through the bean configuration<\/a> file. The properties to be set are defined under the <property> tag in the bean configuration file.<\/p>\n\n\n\n
            Example:<\/strong><\/p>\n\n\n\n
            Step 1: Book.java<\/p>\n\n\n\n
            public class Book {  \n    private int id;  \n    private String bookName;  \n    private String author;  \n    public int getId() {  \n        return id;  \n    }  \n    public void setId(int id) {  \n        this.id = id;  \n    }  \n    public String getBookName() {  \n        return bookName;  \n    }  \n    public void setBookName(String bookName) {  \n        this.bookName = bookName;  \n    }  \n    public String getAuthor() {  \n        return author;  \n    }  \n    public void setAuthor(String author) {  \n        this.author = author;  \n    }  \n    void display(){  \n        System.out.println(id+\" \"+bookName+\" \"+author);  \n    }  \n}\n<\/pre>\n\n\n\n
            Step 2: applicationContext.xml<\/p>\n\n\n\n
            <?xml version=\"1.0\" encoding=\"UTF-8\"?>  \n<beans  \n    xmlns=\"https:\/\/www.springframework.org\/schema\/beans\"  \n    xmlns:xsi=\"https:\/\/www.w3.org\/2001\/XMLSchema-instance\"  \n    xmlns:p=\"https:\/\/www.springframework.org\/schema\/p\"  \n    xsi:schemaLocation=\"https:\/\/www.springframework.org\/schema\/beans  \n                https:\/\/www.springframework.org\/schema\/beans\/spring-beans-3.0.xsd\">  \n<bean id=\"book\" class=\"com.spring.example.Book\">  \n<property name=\"id\">  \n<value>1<\/value>  \n<\/property>  \n<property name=\"bookName\">  \n<value>The Complete Reference J2EE<\/value>  \n<\/property>  \n<property name=\"author\">  \n<value>Herbert Schildt<\/value>  \n<\/property>  \n<\/bean>  \n<\/beans>\n<\/pre>\n\n\n\n
            Step 3: Main.java<\/p>\n\n\n\n
            import org.springframework.beans.factory.BeanFactory;  \nimport org.springframework.beans.factory.xml.XmlBeanFactory;  \nimport org.springframework.core.io.*;  \npublic class Main {  \n    public static void main(String[] args) {  \n        Resource r=new ClassPathResource(\"applicationContext.xml\");  \n        BeanFactory factory=new XmlBeanFactory(r);  \n        Book b=(Book)factory.getBean(\"book\");  \n        b.display();  \n    }  \n}\n<\/pre>\n\n\n\n
            Difference between Setter Dependency Injection and Constructor Dependency Injection:<\/strong><\/h3>\n\n\n\n
            Setter Dependency Injection (SDI)<\/td>Constructor Dependency Injection<\/a> (CDI)<\/td><\/tr>
            Readability is poor, as there is a lot of code in the application.<\/td>Readability is good as dependency is separately present in the code.<\/td><\/tr>
            The bean should include setter and getter methods.<\/td>The bean should contain a matching constructor with argument; otherwise, BeanCreationException will be thrown.<\/td><\/tr>
            It is preferred when properties are less and contain mutable objects.<\/td>It is preferred when properties are more and contain immutable objects.<\/td><\/tr>
            There is a scope of circular dependency, and partial dependency is available.<\/td>There is no scope of circular dependency or partial dependency.<\/td><\/tr>
            It requires @Autowired annotation to increase the coupling between the classes and DI containers.<\/td>It does not require the addition of @Autowired annotation.<\/td><\/tr><\/tbody><\/table><\/figure>\n","protected":false},"excerpt":{"rendered":"
            Dependency Injection is a pattern that is used to remove dependency from the programming code so that it becomes easy to manage and test the application. Dependency Lookup (DL): It is an approach where you get the resources after demand. There are various methods to get resources. To get the resource directly by calling a […]<\/p>\n","protected":false},"author":1,"featured_media":3977,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[42],"tags":[1075,1078,1076,1077],"class_list":["post-3941","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-java-tutorials","tag-constructor-dependency-injection","tag-dependency-lookup","tag-setter-dependency","tag-what-is-dependency-injection"],"_links":{"self":[{"href":"https:\/\/www.h2kinfosys.com\/blog\/wp-json\/wp\/v2\/posts\/3941","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.h2kinfosys.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.h2kinfosys.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.h2kinfosys.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.h2kinfosys.com\/blog\/wp-json\/wp\/v2\/comments?post=3941"}],"version-history":[{"count":1,"href":"https:\/\/www.h2kinfosys.com\/blog\/wp-json\/wp\/v2\/posts\/3941\/revisions"}],"predecessor-version":[{"id":32606,"href":"https:\/\/www.h2kinfosys.com\/blog\/wp-json\/wp\/v2\/posts\/3941\/revisions\/32606"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.h2kinfosys.com\/blog\/wp-json\/wp\/v2\/media\/3977"}],"wp:attachment":[{"href":"https:\/\/www.h2kinfosys.com\/blog\/wp-json\/wp\/v2\/media?parent=3941"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.h2kinfosys.com\/blog\/wp-json\/wp\/v2\/categories?post=3941"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.h2kinfosys.com\/blog\/wp-json\/wp\/v2\/tags?post=3941"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}