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    <p>The warnings only says that <code>x.hashCode() != Objects.hashCode(x)</code> is true. (Okay, this is true most of the time. They could still collide for some values. It's actually not equal for <strong>most</strong> objects.)</p> <p>A valid hashCode/equals implementation is:</p> <pre><code>public class Teacher { private final String name; public Teacher(String name) { this.name = name; } @Override public equals(Object obj){ if(obj == this) return true; if(!(obj instanceof Teacher)) return false; return Objects.equal(name, ((Teacher) obj).getName()); } @Override public hashCode(){ return 0; } } </code></pre> <p>This is a valid although all hash values collide. From hashCode() javadoc:</p> <blockquote> <p>It is not required that if two objects are unequal according to the equals(java.lang.Object) method, then calling the hashCode method on each of the two objects must produce distinct integer results.</p> </blockquote> <p>The difference to a "normal" implementation is that the performance of this code will be much worse. HashMaps for example will degenerate to a lists like performance for lookups.</p> <p>Even with this implementation:</p> <pre><code>@Override public int hashCode() { return Objects.hashCode(Teacher.class, name); } </code></pre> <p>it's possible (but very unlikely) that the hash values of different classes collide. This is the case if the hashes of the class names are the same for both classes. </p> <p>This kind of optimization should be a last resort when there are <strong>a lot</strong> of instances from different types with the <strong>same name</strong> in a collection that <strong>uses hashCode() internally</strong>. The overall efect will be limited: if you have n types you have at most n collisions due to this scenario. Other factors are probable to dominate the performance characteristics. </p>
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    1. POguava-libraries: Is Objects.hashCode(Object[]) collision safe?
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    1. USThomas Jung
    1. USThomas Jung
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    1. COin your equals implementation the line - if(!(obj instanceof Teacher)) return true; should return false instead of true
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      1. USPremraj
    2. CO@Falcon Thanks! Corrected.
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      1. USThomas Jung
 

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