ModifyingCollectionWithItself
Using a collection function with itself as the argument.

Category
Severity
ERROR
Maturity

The problem

Invoking a collection method with the same collection as the argument is likely incorrect.

Suppression

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


Positive examples

ModifyingCollectionWithItselfPositiveCases.java

/*
 * Copyright 2011 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.testdata;

import java.util.ArrayList;
import java.util.List;

/** @author scottjohnson@google.com (Scott Johnson) */
public class ModifyingCollectionWithItselfPositiveCases {

  List<Integer> a = new ArrayList<Integer>();
  List<Integer> c = new ArrayList<Integer>();

  public void addAll(List<Integer> b) {
    // BUG: Diagnostic contains: a.addAll(b)
    this.a.addAll(a);

    // BUG: Diagnostic contains: a.addAll(1, b)
    a.addAll(1, a);
  }

  public void containsAll(List<Integer> b) {
    // BUG: Diagnostic contains: this.a.containsAll(b)
    this.a.containsAll(this.a);

    // BUG: Diagnostic contains: a.containsAll(b)
    a.containsAll(this.a);
  }

  public void retainAll(List<Integer> a) {
    // BUG: Diagnostic contains: this.a.retainAll(a)
    a.retainAll(a);
  }

  public void removeAll() {
    // BUG: Diagnostic contains: a.clear()
    this.a.removeAll(a);

    // BUG: Diagnostic contains: a.clear()
    a.removeAll(a);
  }

  static class HasOneField {
    List<Integer> a;

    void removeAll() {
      // BUG: Diagnostic contains: a.clear();
      a.removeAll(a);
    }

    void testParameterFirst(List<Integer> b) {
      // BUG: Diagnostic contains: this.a.removeAll(b);
      b.removeAll(b);
    }

    void expressionStatementChecks() {
      // BUG: Diagnostic contains: ModifyingCollectionWithItself
      boolean b = 2 == 2 && a.containsAll(a);

      // BUG: Diagnostic contains: ModifyingCollectionWithItself
      b = a.retainAll(a);

      // BUG: Diagnostic contains: ModifyingCollectionWithItself
      b = a.removeAll(a);
    }
  }
}

Negative examples

ModifyingCollectionWithItselfNegativeCases.java

/*
 * Copyright 2011 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.testdata;

import java.util.ArrayList;
import java.util.List;

/** @author scottjohnson@google.com (Scott Johnson) */
public class ModifyingCollectionWithItselfNegativeCases {

  List<Integer> a = new ArrayList<Integer>();

  public boolean addAll(List<Integer> b) {
    return a.addAll(b);
  }

  public boolean removeAll(List<Integer> b) {
    return a.removeAll(b);
  }

  public boolean retainAll(List<Integer> b) {
    return a.retainAll(b);
  }

  public boolean containsAll(List<Integer> b) {
    return a.containsAll(b);
  }
}