MoreThanOneInjectableConstructor
This class has more than one @Inject-annotated constructor. Please remove the @Inject annotation from all but one of them.

Category
Severity
ERROR
Maturity

Alternate names: inject-constructors, InjectMultipleAtInjectConstructors

The problem

Injection frameworks may use @Inject to determine how to construct an object in the absence of other instructions. Annotating @Inject on a constructor tells the injection framework to use that constructor. However, if multiple @Inject constructors exist, injection frameworks can’t reliably choose between them.

Suppression

Suppress false positives by adding an @SuppressWarnings("MoreThanOneInjectableConstructor") annotation to the enclosing element.


Positive examples

MoreThanOneInjectableConstructorPositiveCases.java

/*
 * Copyright 2013 Google Inc. All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.errorprone.bugpatterns.inject.testdata;

import com.google.inject.Inject;
import java.beans.ConstructorProperties;

/** @author sgoldfeder@google.com(Steven Goldfeder) */
public class MoreThanOneInjectableConstructorPositiveCases {

  /** Class has 2 constructors, both are injectable */
  // BUG: Diagnostic contains: MoreThanOneInjectableConstructor
  public class TestClass1 {
    @Inject
    public TestClass1() {}

    @Inject
    public TestClass1(int n) {}
  }

  /** Class has 3 constructors, two of which are injectable. */
  // BUG: Diagnostic contains: MoreThanOneInjectableConstructor
  public class TestClass2 {
    @Inject
    public TestClass2() {}

    public TestClass2(int n) {}

    @Inject
    public TestClass2(String s) {}
  }

  /**
   * testing that the error appears on the @Inject annotation even in the presence of other
   * annotations
   */
  // BUG: Diagnostic contains: MoreThanOneInjectableConstructor
  public class TestClass3 {
    @Inject
    public TestClass3() {}

    @Inject
    @ConstructorProperties({"m", "n"})
    public TestClass3(int m, int n) {}
  }

  /** Fails on 3 constructors w/ @Inject */
  // BUG: Diagnostic contains: MoreThanOneInjectableConstructor
  public class TestClass4 {
    @Inject
    public TestClass4() {}

    @Inject
    public TestClass4(int m, int n) {}

    @Inject
    public TestClass4(int m, int n, boolean x) {}
  }
}

Negative examples

MoreThanOneInjectableConstructorNegativeCases.java

/*
 * Copyright 2013 Google Inc. All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.errorprone.bugpatterns.inject.testdata;

import com.google.inject.Inject;

/** @author sgoldfeder@google.com(Steven Goldfeder) */
public class MoreThanOneInjectableConstructorNegativeCases {

  /** Class has a single non-injectable constructor. */
  public class TestClass1 {
    public TestClass1() {}
  }

  /** Class has a single injectable constructor. */
  public class TestClass2 {
    @Inject
    public TestClass2() {}
  }

  /** Class has two constructors, one of which is injectable. */
  public class TestClass3 {
    @Inject
    public TestClass3() {}

    public TestClass3(int n) {}
  }

  /** Class has two constructors, one of which is injectable. Class also has an injectable field. */
  public class TestClass4 {

    @Inject String x;

    @Inject
    public TestClass4() {}

    public TestClass4(int n) {}
  }

  /** Class has 2 constructors, both are injectable. Error is suppressed. */
  @SuppressWarnings("MoreThanOneInjectableConstructor")
  public class TestClass5 {
    @Inject
    public TestClass5() {}

    @Inject
    public TestClass5(int n) {}
  }

  /** Suppressed class */
  @SuppressWarnings("inject-constructors")
  public class TestClass6 {
    @Inject
    public TestClass6() {}

    @Inject
    public TestClass6(int n) {}
  }

  /** Suppressed class */
  @SuppressWarnings("InjectMultipleAtInjectConstructors")
  public class TestClass7 {
    @Inject
    public TestClass7() {}

    @Inject
    public TestClass7(int n) {}
  }
}