Annotations and Reflection

Enum Reflection

Enum metadata exposes the constants declared by an enum type.

enum constants getEnumConstants returns the enum values in declaration order.
ordinal An enum ordinal is its zero-based position in the declaration.

Enum Reflection

index
EnumReflection.java
Replay: real traced execution (multi-file project)
public class EnumReflection {
    enum Status {
        READY,
        RUNNING,
        DONE
    }

    public static void main(String[] args) {
        int index = 0;
        Status[] values = Status.class.getEnumConstants();
        Status status = values[index];

        System.out.println("name=" + status.name());
        System.out.println("ordinal=" + status.ordinal());
    }
}

public class EnumReflection {
    enum Status {
        READY,
        RUNNING,
        DONE
    }

    public static void main(String[] args) {
        int index = 1;
        Status[] values = Status.class.getEnumConstants();
        Status status = values[index];

        System.out.println("name=" + status.name());
        System.out.println("ordinal=" + status.ordinal());
    }
}

public class EnumReflection {
    enum Status {
        READY,
        RUNNING,
        DONE
    }

    public static void main(String[] args) {
        int index = 2;
        Status[] values = Status.class.getEnumConstants();
        Status status = values[index];

        System.out.println("name=" + status.name());
        System.out.println("ordinal=" + status.ordinal());
    }
}

  1. index ← 0, status ← READY

    8public static void main(String[] args) {9    int index→ 0 = 0;  //@index=1, 210    Status[] values = Status.class.getEnumConstants();11    Status status→ READY = values[index]READY;1213    System.out.println("name=" + status.name());14    System.out.println("ordinal=" + status.ordinal());15}
    outputname=READY
ordinal=0

  1. index ← 1, status ← RUNNING

    8public static void main(String[] args) {9    int index→ 1 = 1;10    Status[] values = Status.class.getEnumConstants();11    Status status→ RUNNING = values[index]RUNNING;1213    System.out.println("name=" + status.name());14    System.out.println("ordinal=" + status.ordinal());15}
    outputname=RUNNING
ordinal=1

  1. index ← 2, status ← DONE

    8public static void main(String[] args) {9    int index→ 2 = 2;10    Status[] values = Status.class.getEnumConstants();11    Status status→ DONE = values[index]DONE;1213    System.out.println("name=" + status.name());14    System.out.println("ordinal=" + status.ordinal());15}
    outputname=DONE
ordinal=2