EqualsNaN
== NaN always returns false; use the isNaN methods instead

Category
Severity
ERROR
Maturity

The problem

As per JLS 15.21.1, == NaN comparisons always return false, even NaN == NaN. Instead, use the isNaN methods to check for NaN.

Suppression

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


Positive examples

EqualsNaNPositiveCases.java

/*
 * Copyright 2014 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;

/** @author lowasser@google.com (Louis Wasserman) */
public class EqualsNaNPositiveCases {

  // BUG: Diagnostic contains: Double.isNaN(0.0)
  static final boolean ZERO_DOUBLE_NAN = 0.0 == Double.NaN;

  // BUG: Diagnostic contains: !Double.isNaN(1.0)
  static final boolean ONE_NOT_DOUBLE_NAN = Double.NaN != 1.0;

  // BUG: Diagnostic contains: Float.isNaN(2.f)
  static final boolean TWO_FLOAT_NAN = 2.f == Float.NaN;

  // BUG: Diagnostic contains: !Float.isNaN(3.0f)
  static final boolean THREE_NOT_FLOAT_NAN = 3.0f != Float.NaN;

  // BUG: Diagnostic contains: Double.isNaN(Double.NaN)
  static final boolean NAN_IS_NAN = Double.NaN == Double.NaN;

  // BUG: Diagnostic contains: Double.isNaN(123456)
  static final boolean INT_IS_NAN = 123456 == Double.NaN;
}

Negative examples

EqualsNaNNegativeCases.java

/*
 * Copyright 2014 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;

/** @author lowasser@google.com (Louis Wasserman) */
public class EqualsNaNNegativeCases {
  static final boolean NAN_AFTER_MATH = (0.0 / 0.0) == 1.0;
  static final boolean NORMAL_COMPARISON = 1.0 == 2.0;
}