How can I list enum values and concatenate id in Java

Question

I have an enum like this:

public enum  DocumentType {
    A,
    B,
    C,
    D;
}

I want a list like this:

1 A
2 B
3 C
4 D 

Answer 1

public class EnumId {
    public enum DocumentType {
        A(1), B(2), C(3), D(4);

        final int id;

        DocumentType(int id) {
            this.id = id;
        }

        int getId() {
            return this.id;
        }
    }

    public static void main(String[] args) {
        for (DocumentType dt : DocumentType.values())
            System.out.println(dt.getId() + " " + dt.name());
    }
}

$ javac EnumId.java
$ java EnumId      
1 A
2 B
3 C
4 D
$ 

Answer 2

You can even use ordinal & name methods available in Enum; this don't need you to modify anything in existing DocumentType :

for(DocumentType e:DocumentType.values()) {
            System.out.println((e.ordinal()+1)+" "+e.name());
}

Output:

1 A
2 B
3 C
4 D 

Answer 3

Since you want to return this in a response you could do something like this:

public String yourEndpoit() {
    final DocumentType[] values = DocumentType.values();

    final StringBuilder builder = new StringBuilder();
    for (int i = 0; i < values.length; i++) {
        builder.append(i)
                .append(" ")
                .append(values[i])
                .append(System.lineSeparator());
    }
        
    return builder.toString();
}

Answer 4

A solution that leverages method declarations within enumerated types:

public enum DocumentType {
    A, B, C, D;
    
    public String asListItem() {
        return String.format("%d %s", ordinal()+1, name());
    }
    
    public static String toList() {
        return Arrays.stream(values())
                .map(DocumentType::asListItem)
                .collect(Collectors.joining("\n"));
    }
}

To get the list: DocumentType.toList().