How do I switch on values defined inside a java enum of strings

Question

I have the following code :

class MyClass {
    private Value value;
    public enum Value {
        INSERT_ONLY("INSERT_ONLY"), UPDATE_ONLY("UPDATE_ONLY"), UPSERT("UPSERT") ;
        private final String val ;
        private Value(final String v) {val = v ;}
        public String toString() {return val ;}     
        public String getVal() {
            return val;
        }
    } ;
    public Value getValue() {
        return value;
    }
    public void setValue(Value value) {
        this.value = value;
    }
}

public class one {
    public static void main(String[] args) {
        MyClass obj = new MyClass() ;
        obj.setValue(MyClass.Value.INSERT_ONLY) ;

        String s = obj.getValue().toString() ;
        String s1 = MyClass.Value.INSERT_ONLY.toString() ;
        switch(s) {
            case "INSERT_ONLY" : System.out.println("INSERT_ONLY") ;
                break ;
            case "s2" : System.out.println("s2") ;
                break ;
        }
    }
}

This code works. But what I want is that in switch-case I use the strings as defined in the enum Value. If I use s1 in case, it generates an error. What is the way out?

Which version of Java are you using? What's the error? – shmosel Sep 05 '16 at 18:33 — shmosel, Sep 05 '16 at 18:33
I want to use `s1` in `case` AND NOT in `switch` – user3282758 Sep 06 '16 at 06:58 — user3282758, Sep 06 '16 at 06:58

score 1 · Answer 1 · answered Sep 05 '16 at 18:30

Enums have a method .name() that returns the enum as a String. All your "values" are equivalent to this - just switch on that.

You can delete the value field, the constructor and getter and call name() where you are currently calling getValue().

Further, the default implementation of toString() returns name() so you can delete your toString() method without having any effect.

Finally, you can switch on the enum itself.

score 0 · Answer 2 · answered Sep 05 '16 at 18:30

0

you string in the enum is actually the same as the enumertor constants... so it is a little redundant and completely unnescessary...

try this:

enum Value {
    INSERT_ONLY, UPDATE_ONLY, UPSERT;
}

public static void main(String[] args)  {
Week obj = new Week() ;
Value s = obj.getValue( ) ;
        switch(s) {
            case INSERT_ONLY : System.out.println("INSERT_ONLY") ;
                break ;
            case UPDATE_ONLY : System.out.println("UPDATE_ONLY") ;
                break ;
        }
    }
}

answered Sep 05 '16 at 18:30

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I need those Strings as I have to ultimately convert the objects of `MyClass` to-and-fro to json objects – user3282758 Sep 06 '16 at 06:55
every constant of that Enum can be printed as string if you call the method name() – ΦXocę 웃 Пepeúpa ツ Sep 06 '16 at 07:09

score 0 · Answer 3 · edited May 23 '17 at 12:16

You could try it this way:

MyClass.Value value = obj.getValue() ;
switch(value) {
  case INSERT_ONLY : System.out.println("INSERT_ONLY") ;
    break ;
  case UPSERT : System.out.println("Upsert") ;
    break ;
  case UPDATE_ONLY : System.out.println("Update only") ;
   break ;
 }

Basically, the switch-statement uses the enum-names. So there is no need to apply the toString()-method on the Value returned by obj.getValue().

If you would like to know why switch will not work in combination with strings, please have a look here. One more suggestion: add also the default-branch to the switch-statement.

score 0 · Answer 4 · edited May 23 '17 at 12:01

If I understand correctly, you're trying to look up an enum constant by an unknown string s. The reason your case expression can't be s1 is because it must be a compile-time constant, which s1 is not. Since your example seems to be mostly theoretical, I'll suggest a few options and you can pick the most appropriate for your actual case:

Assuming the enum names are the same as their values (in which case you can scrap the field entirely) and you're just trying to look up an enum by its name, just do this:
```
MyClass.Value v = MyClass.Value.valueOf(s);
```
This will throw an IllegalArgumentException if no mapping is found for s1.

Still assuming the names are the same, but you do need an actual switch with some additional cases and custom logic:

try {
    MyClass.Value v = MyClass.Value.valueOf(s);
    switch (v) {
        case INSERT_ONLY : System.out.println("INSERT_ONLY") ;
            break ;
    }
} catch (IllegalArgumentException e) {
    switch (s)
        case "s2" : System.out.println("s2") ;
            break ;
    }
}

If the names are not actually the same, you can add a static map of constants inside the enum class, to simulate valueOf():

public enum Value {
    ONLY_INSERT("ONLY_INSE"), ONLY_UPDATE("UPDATE_ONLY"), UPSERT("UPSERT") ;

    private static final Map<String, Value> byName = new HashMap<>();
    static {
        for (Value v : values()) {
            byName.put(v.getVal(), v);
        }
    }

    public static Value byName(String name) {
        Value result = byName.get(name);
        if (result == null) {
            throw new IllegalArgumentException("Invalid name" + name);
        }
        return result;
    }

    private final String val ;
    private Value(final String v) {val = v ;}
    public String toString() {return val ;}     
    public String getVal() {
        return val;
    }
} ;

Now you can do the same as the previous solutions, using MyClass.Value.byName().

How do I switch on values defined inside a java enum of strings

4 Answers4