Overriding equals() and not hashCode()

[cushon]

Original issue created by maekawa@google.com on 2013-07-03 at 04:51 AM

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Describe the bug pattern this checker should detect and why it is
incorrect.

Note our criteria for new checks:
https://code.google.com/p/error-prone/wiki/NewCheckCriteria

If possible, please attach source files that contain code that should and
should not trigger the error. Code that should trigger the error should
be in a file called PositiveCases.java, and code that should not trigger
the error should be in a file called NegativeCases.java.

Otherwise, just include positive and negative cases below.

When we override equals(), we should almost always override hashCode() too.

// Positive
class Foo {
  int a;

  @Override
  public boolean equals(Object o) {
    if (o instanceof Foo) {
      return a == ((Foo) o).a;
    }
    return false;
  }
}

// Negative
class Bar {
  int a;

  @Override
  public boolean equals(Object o) {
    if (o instanceof Bar) {
      return a == ((Bar) o).a;
    }
    return false;
  }

  @Override
  public int hashCode() {
    return a;
  }
}

[cushon]

Original comment posted by aeagle22206 on 2013-08-12 at 09:09 PM

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(No comment entered for this change.)

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Status: Duplicate
Merged Into: #129