Need Programming Help With the "enum" Type of Variable

[Natalie Kopple]

I have never used variables with the "enum" type. I have several questions in regard to its uses. The questions are marked in the code snippet show below. I appreciate your help. Thank you.

package abc;

public class AAA {
     public void method() {
        RequestRouter requestRouter = new RequestRouter();
        what_is_the_variable_here = requestRouter.determinePath( userRequestURI ) ;       // based on the "what_is_the_variable_here", code if else statements below.     

    }
}



package abc;

public class RequestRouter {
    public ???return_type??? determinePath( URI userRequestURI ) {    // what is the return type of this method?

        private enum requestType { PATH_ONE, PATH_TWO, PATH_THREE };
        // parse the userRequestURI to find out which path (PATH_ONE or PATH_TWO or PATH_THREE) is requested.

        return requestType;     // want to return only one of the three paths
    }
}

[Stephan van Hulst]

Hi Natalie, your code could look as follows:

class RequestRouter {

  static enum RequestType {
    PATH_ONE,
    PATH_TWO,
    PATH_THREE
  }

  RequestType determinePath(URI userRequestURI) {
    return RequestType.PATH_ONE; // for example
  }
}

class AAA {

  void method() {
    RequestRouter requestRouter = new RequestRouter();
    RequestRouter.RequestType type = requestRouter.determinePath(null);
  }
}

[Natalie Kopple]

I have modified my code to the one shown below:

package abc;
public enum RequestTypes {ONE_PASS, TWO_PASS, NAVIGATION }

  
package abc;   
  
public class RequestRouter {   
    public RequestTypes determinePath( URI userRequestURI ) {    
  
        // parse the userRequestURI to find out which path (PATH_ONE or PATH_TWO or PATH_THREE) is requested.   
		requestType = RequestTypes.ONE_PASS;
        return requestType;     
    }   
}  


package abc;   
  
public class AAA { 
	 private RequestTypes requestType;
     public void method() {   
        RequestRouter requestRouter = new RequestRouter();   
        requestType = requestRouter.determinePath( userRequestURI ) ;              
    }   
}   

Question: Does the comparison of RequestTypes.PATH_ONE.equals("PATH_ONE") is evaluated to true? where requestType = RequestTypes.PATH_ONE;

[Campbell Ritchie]

If you look in the Java Language Specification, you find that enums are true singletons, ie the JVM only ever has one instance of each. That means you can use the == operator.

Try this sort of thing:-

if (requestRouter.determinePath( userRequestURI ) == RequestTypes.TWO_PASS)
{
   system.out.println("TWO PASS");
}

There is also a section in the Java Tutorials.

[Campbell Ritchie]

I earlier wrote:. . . There is also a section in the Java Tutorials.

. . . which tells you how to use enum constants in a switch-case structure. Maybe that will help you.

[Natalie Kopple]

Thanks very much for your help and support. Now, I have a better idea about "enum".

[Natalie Kopple]

I am still a little confused. If you would not mind helping again:

The question is if we have an "enum" variable A. And another variable B is assigned a value of one of the elements in variable A. What is the data type of variable B? Thanks.

package abc;   
public enum RequestTypes {ONE_PASS, TWO_PASS, NAVIGATION }   
  
     
package abc;      
     
public class RequestRouter {      
    public ???????? determinePath( URI userRequestURI ) {       // what data type is returned?  
     
        // parse the userRequestURI to find out which path (PATH_ONE or PATH_TWO or PATH_THREE) is requested.      
        requestType = RequestTypes.ONE_PASS;   
        return requestType;      // What is the data type of the "requestType"?  
    }      
}     

[Matthew Brown]

The type is the name of the enum: RequestTypes

enums are a specialised type of class, so you'd use the name of the enum in the same way as you'd use the name of the class. Behind the scenes, the compiler will create a class called RequestTypes.

One way of confirming this would be to add this somewhere:

System.out.println(RequestTypes.ONE_PASS.getClass().getName());

[Natalie Kopple]

Thanks very much.