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 the suppression annotation @SuppressWarnings("ModifyingCollectionWithItself") 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);
}
}