Qualifying By Annotation

In addition to being able to qualify by name, you can build your own qualifiers using the Qualifier annotation. For example, consider the following annotation:

import javax.inject.Qualifier;
import java.lang.annotation.Retention;
import static java.lang.annotation.RetentionPolicy.RUNTIME;
@Qualifier
@Retention(RUNTIME)
public @interface V8 {
}

import javax.inject.Qualifier
import java.lang.annotation.Retention
import static java.lang.annotation.RetentionPolicy.RUNTIME
@Qualifier
@Retention(RUNTIME)
@interface V8 {
}

import javax.inject.Qualifier
import java.lang.annotation.Retention
import java.lang.annotation.RetentionPolicy.RUNTIME
@Qualifier
@Retention(RUNTIME)
annotation class V8

The above annotation is itself annotated with the @Qualifier annotation to designate it as a qualifier. You can then use the annotation at any injection point in your code. For example:

    @Inject Vehicle(@V8 Engine engine) {
        this.engine = engine;
    }

    @Inject Vehicle(@V8 Engine engine) {
        this.engine = engine
    }

@Inject constructor(@V8 val engine: Engine) {