Google Guice – Linked Binding

In Linked bindings, Guice maps a type to its implementation. In
example discussed below, we have mapped SpellChecker interface
with its implementation SpellCheckerImpl.

bind(SpellChecker.class).to(SpellCheckerImpl.class);

We can also mapped the concrete class to its subclass. See the
example below −

bind(SpellCheckerImpl.class).to(WinWordSpellCheckerImpl.class);

Observe that here we have chained the bindings. Let us see the
result in complete example.

• Complete Example
• Output

Complete Example

Create a java class named GuiceTester.

GuiceTester.java

import com.google.inject.AbstractModule;
import com.google.inject.Guice;
import com.google.inject.Inject;
import com.google.inject.Injector;

public class GuiceTester {
   public static void main(String[] args) {
      Injector injector = Guice.createInjector(new TextEditorModule());
      TextEditor editor = injector.getInstance(TextEditor.class);
      editor.makeSpellCheck(); 
   } 
}
class TextEditor {
   private SpellChecker spellChecker;
   @Inject
   
   public TextEditor(SpellChecker spellChecker) {
      this.spellChecker = spellChecker;
   }
   public void makeSpellCheck() {
      spellChecker.checkSpelling();
   }
}

//Binding Module
class TextEditorModule extends AbstractModule {
   @Override
   
   protected void configure() {
      bind(SpellChecker.class).to(SpellCheckerImpl.class);
      bind(SpellCheckerImpl.class).to(WinWordSpellCheckerImpl.class);
   } 
}

//spell checker interface
interface SpellChecker {
   public void checkSpelling();
}

//spell checker implementation
class SpellCheckerImpl implements SpellChecker {
   @Override
   
   public void checkSpelling() {
      System.out.println("Inside checkSpelling." );
   } 
}

//subclass of SpellCheckerImpl
class WinWordSpellCheckerImpl extends SpellCheckerImpl {
   @Override
   
   public void checkSpelling() {
      System.out.println("Inside WinWordSpellCheckerImpl.checkSpelling." );
   } 
}

Output

Compile and run the file, you will see the following output.

Inside WinWordSpellCheckerImpl.checkSpelling.