Java Enum utilization example

When I used Java for work before, there was a process that was difficult to understand, so I refactored it.

Before refactoring

It was like this before the refactoring.

   private void doProcess() {
      A a = initial(); 
      if (!chkfnc1(a)) {
        throw new XXXException(x1);
      }

      if (!chkfnc2(a)) {
        throw new XXXException(x2);         
      }
      
      if (!chkfnc3(a)) {
        throw new XXXException(x3);         
      }
      
      
     execute(a); //Execution processing after check
     
   }

  private boolean chkfnc1(a) {}
  private boolean chkfnc2(a) {}
  private boolean chkfnc3(a) {}
  

Instance acquisition-> Instance legitimacy check (n times)-> Execution processing It is a flow.

Suppose chkfncN flows in a sequence and has an order dependency.

If this situation continues, if the check requirement increases by one, it will be difficult to determine when the chkfncN function will be checked, and it will be disgusting.

Enum When you hear the Enum,

--Correspondence with numerical values can be taken --Cases can be separated by switch-case

And so on. I think the biggest feature I think is that the order is guaranteed.

Also part of the Haskell typeclass Enum definition

class Enum a where
 succ :: a -> a --Function showing the following values
 pred :: a -> a --Function showing the previous value

Is defined.

Also in Java Enum

  
for (DaysOfWeekEnum day : DaysOfWeekEnum.values()) {
}

It can be processed in order like this

Features in Java Enums

Java Enums ** Functions can be defined inside Enums ** https://qiita.com/KeithYokoma/items/9681b130ea132cfad64d

combine

Based on the above, you can do this.

public enum MyChecker {
    CHK1 {
        @Override
        public boolean chkfnc(A a) {}
        @Override
        public String erroMsg(){}
    },
    CHK2 {
        @Override
        public boolean chkfnc(A a) {}
        @Override
        public String erroMsg(){}
    };
    CHK3 {
        @Override
        public boolean chkfnc(A a) {}
        @Override
        public String erroMsg(){}
    };
    public abstract boolean chkfnc(A a);
    public abstract String errorMsg;
}

Using the previous example

private void doProcess() {
  A a = initial();
  for (MyChecker val : MyChecker.values()) {
     if (!val.chefnc) {
       throw new XXXException(val.erroMsg);
     }
  }
}

And the inside of doProcess was refreshed and the view became better. Also, since the order is guaranteed by using Enum, it is almost as if you want to guarantee the operation.

Summary

There weren't many articles that used Enum valies in Java like this, so I wrote it. The situation where it can be used is limited, but if you recognize that the enum guarantees the order, I think that other applications will also work.