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

Severity
ERROR
Has Fix?
NO_FIX

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 the suppression annotation @SuppressWarnings("MoreThanOneInjectableConstructor") to the enclosing element.


Positive examples

MoreThanOneInjectableConstructorPositiveCases.java

/*
* Copyright 2013 The Error Prone Authors.
*
* 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 The Error Prone Authors.
*
* 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) {}
}
}