Because ``++Object++`` implements ``++hashCode++``, any Java class can be put into a hash structure. However, classes that define ``++equals(Object)++`` but not ``++hashCode()++`` aren't truly hash-able because instances that are equivalent according to the ``++equals++`` method can return different hashes.


== Noncompliant Code Example

----
public class Student {  // no hashCode() method; not hash-able
  // ...

  public boolean equals(Object o) {
    // ...
  }
}

public class School {
  private Map<Student, Integer> studentBody = // okay so far
          new HashTable<Student, Integer>(); // Noncompliant

  // ...
----


== Compliant Solution

----
public class Student {  // has hashCode() method; hash-able
  // ...

  public boolean equals(Object o) {
    // ...
  }
  public int hashCode() {
    // ...
  }
}

public class School {
  private Map<Student, Integer> studentBody = new HashTable<Student, Integer>();

  // ...
----



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