Question

Java’s Collections.checked*() api gives us type-safe views to underlying collections. But the checks happen at runtime and throw a runtime exception which can be costly for performance. The same type checking can be enforced at compile time by giving a specific type to those collections by using generic collections. So are there situations where Collections.checked*() scores over generic collections with their types specified?

Answer 1

The javadoc explains it well:

http://download.oracle.com/javase/6/docs/api/java/util/Collections.html#checkedCollection%28java.util.Collection,%20java.lang.Class%29

The generics mechanism in the language provides compile-time (static) type checking, but it is possible to defeat this mechanism with unchecked casts. Usually this is not a problem, as the compiler issues warnings on all such unchecked operations. There are, however, times when static type checking alone is not sufficient. For example, suppose a collection is passed to a third-party library and it is imperative that the library code not corrupt the collection by inserting an element of the wrong type.