greenrobot/greenDAO · error · RuntimeException

Interface defined more than once:

Error message

Interface defined more than once: 

What it means

Entity.implementsInterface rejects adding the same interface name twice to an entity's implements list. Duplicates would emit an invalid Java class declaration (implements Foo, Foo), so the generator throws a RuntimeException immediately during schema building.

Solutions

1. Deduplicate the interface list before passing it to implementsInterface (e.g. new LinkedHashSet<>(Arrays.asList(...))).
2. Remove redundant implementsInterface calls for interfaces already declared.
3. Don't pass "Serializable" via implementsInterface when implementsSerializable() is already used.
4. Guard call sites with entity.getInterfaces().contains(name) checks before adding.

Example fix

// before
entity.implementsSerializable();
entity.implementsInterface("java.io.Serializable"); // duplicate
// after
entity.implementsSerializable(); // only once

List<String> distinct = new ArrayList<>(new LinkedHashSet<>(Arrays.asList(interfaces)));
entity.implementsInterface(distinct.toArray(new String[0]));

try {
    entity.implementsInterface(names);
} catch (RuntimeException e) {
    if (e.getMessage().startsWith("Interface defined more than once")) {
        log.warn("Deduplicating interfaces for " + entity.getClassName());
        return;
    }
    throw e;
}

When it happens

Trigger: Calling entity.implementsInterface("Comparable", "Comparable") or invoking implementsInterface multiple times with overlapping names; using both implementsSerializable() and implementsInterface("Serializable").

Common situations: Varargs call sites built from collections that may contain repeats; configuration-driven entity setup where a base config and a per-entity config both add the same interface; combining implementsSerializable() with an explicit "java.io.Serializable" entry.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

• Property already defined:
• Duplicate name for
• No DAO registered for
• Could not init DAOConfig
• Duplicate property ordinals

AI-assisted analysis of greenrobot/greenDAO@0bbb338e17 (2026-09-08). Data as JSON: /api/errors/61b5c50034f280fc. Report an issue: GitHub.

Appendix: source

Thrown at DaoGenerator/src/org/greenrobot/greendao/generator/Entity.java:472

        return additionalImportsDao;
    }

    public void setHasKeepSections(Boolean hasKeepSections) {
        this.hasKeepSections = hasKeepSections;
    }

    public List<String> getInterfacesToImplement() {
        return interfacesToImplement;
    }

    public List<ContentProvider> getContentProviders() {
        return contentProviders;
    }

    public void implementsInterface(String... interfaces) {
        for (String interfaceToImplement : interfaces) {
            if (interfacesToImplement.contains(interfaceToImplement)) {
                throw new RuntimeException("Interface defined more than once: " + interfaceToImplement);
            }
            interfacesToImplement.add(interfaceToImplement);
        }
    }

    public void implementsSerializable() {
        interfacesToImplement.add("java.io.Serializable");
    }

    public String getSuperclass() {
        return superclass;
    }

    public void setSuperclass(String classToExtend) {
        this.superclass = classToExtend;
    }

    public String getJavaDoc() {

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