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The interfaces of the Java Collections Framework [JCF 2014] use generically typed, parameterized methods, such as add(E e) and put(K key, V value), to insert objects into the collection or map, but they have other methods, such as contains(), remove(), or get(), that accept an argument of type Object rather than a parameterized type. TheoreticallyConsequently, this enables a programmer to attempt to remove methods accept an object of any type. The collections framework interfaces were designed in this manner to maximize backwards compatibility but this can also lead to coding errors. Programmers must ensure that arguments passed to methods such as Map<K,V> get(), Collection<E>  contains(), and remove() have the same type as the parameterized type of the corresponding class instance.

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import java.util.HashSet;
 
public class ShortSet {
  public static void main(String[] args) {
    HashSet<Short> s = new HashSet<Short>();
	for (int i = 0; i < 10; i++) {
	  s.add((short)i);
	  // remove a Short
	  if (s.remove((short)i) == false) {
	    System.err.println("Error removing " + i);
	  }
	}
	System.out.println(s.size());
  }
}

Exceptions

EXP04-EX0EX1: The collections framework equals() method also takes an argument of type Object, but it is acceptable to pass an object of a different type from that of the underlying collection/map to the equals() method. Doing so cannot cause any confusion because the contract of the equals() method stipulates that objects of different classes will never be equivalent. See MET08-J. Preserve the equality contract when overriding the equals() method for more information.

EXP04-EX2: Some Java programs, particularly legacy programs, may iterate through a collection of variously typed objects with the expectation that only those objects with the same type as the collection parameter will be operated on.  An exception is allowed in cases where there is no expectation that the operation is not a no-op.

Risk Assessment

Passing arguments to certain Java Collection Framework methods that are of a different type from that of the class instance can cause silent failures, resulting in unintended object retention, memory leaks, or incorrect program operation [Techtalk 2007].

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02. Expressions (EXP) EXP05-J. Do not write more than once to the same variable within an expression