what is the values() that I have seen in various CDI qualifiers in java? -

good day.

i have seen various references values() inside @qualifier definitions. understand @qualifier tagging system, yet define them interface.

an interface can allow enums, don't understand word 'values()' i've seen in 2 unrelated examples i've listed below.

could please explain me word values() means?

@qualifier @retention(runtime) @target({field, type, method}) public @interface numberofdigits {     digits value(); }  public enum digits {     two,     eight,     ten,     thirteen } 

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package com.byteslounge.bean;  import static java.lang.annotation.elementtype.field; import static java.lang.annotation.elementtype.type; import static java.lang.annotation.elementtype.method; import static java.lang.annotation.retentionpolicy.runtime; import java.lang.annotation.retention; import java.lang.annotation.target;  import javax.inject.qualifier;  @qualifier @retention(runtime) @target({field, type, method}) public @interface messagetransport {    messagetransporttype value();  } 

these not interfaces. these annotations. possible declare static information on annotations , annotate them. code inspects annotations can utilize information.

annotations declared qualifiers let cdi disambiguate between implementations of same type.

consider qualifier foo:

@qualifier @retention(runtime) @target({field, type, method}) public @interface foo { int value(); } 

types annotated foo:

@foo(1) public class bar implements runnable {    //...impl  @foo(2) public class baz implements runnable {    //...impl 

a cdi bean:

public class bean {   @inject @foo(1) runnable a;   @inject @foo(2) runnable b;   //...impl 

here, a resolved instance of bar while b resolved instance of baz.

without qualifier annotation, cdi api wouldn't able tell instance of runnable inject. values must exact match.