EqualsReference
== must be used in equals method to check equality to itself or an infinite loop will occur.

Category
JDK
Severity
ERROR
Maturity

The problem

.equals() to the same object will result in infinite recursion

Suppression

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


Positive examples

EqualsReferencePositiveCases.java

/*
 * Copyright 2017 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;

/** Created by mariasam on 6/22/17. */
public class EqualsReferencePositiveCases {

  @Override
  // BUG: Diagnostic contains: ==
  public boolean equals(Object o) {
    System.out.println(this.equals(o));
    return true;
  }

  class EqualsInElse {
    @Override
    // BUG: Diagnostic contains: ==
    public boolean equals(Object o) {
      System.out.println(o == this);
      return this.equals(o);
    }
  }

  class FinalObject {
    @Override
    // BUG: Diagnostic contains: ==
    public boolean equals(final Object object) {
      return this.equals(object);
    }
  }

  class NoThis {
    @Override
    // BUG: Diagnostic contains: ==
    public boolean equals(Object o) {
      return equals(o);
    }
  }
}

Negative examples

EqualsReferenceNegativeCases.java

/*
 * Copyright 2017 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;

/** Created by mariasam on 6/23/17. */
public class EqualsReferenceNegativeCases {

  @Override
  public boolean equals(Object o) {
    return (this == o);
  }

  class OtherEquals {
    @Override
    public boolean equals(Object o) {
      if (o.equals("hi")) {
        return true;
      } else {
        return o == this;
      }
    }
  }

  class EqualsThisLast {
    @Override
    public boolean equals(Object o) {
      if (o instanceof EqualsThisLast) {
        return true;
      }
      return o.equals(this);
    }
  }

  class Foo {
    @Override
    public boolean equals(Object o) {
      return o instanceof Foo && this.equals((Foo) o);
    }

    public boolean equals(Foo o) {
      return true;
    }
  }

  class OtherEqualsMethod {
    @Override
    public boolean equals(Object o) {
      return equals((String) o);
    }

    public boolean equals(String o) {
      return true;
    }
  }

  class CodeBase {
    public CodeBase(Object o) {}

    public boolean equals(Object obj) {
      CodeBase other = (CodeBase) obj;
      return equals(new CodeBase(other.getValue()));
    }

    public Object getValue() {
      return null;
    }
  }
}