The Interfaces you’re most likely to implement are:
java.lang.Comparable
java.lang.Runnable
java.io.Serializable
Interfaces that you’re most likely to call methods on but not implement yourself are:
java.lang.Appendable (StringBuffer / StringBuilder / Writers)
java.lang.CharSequence (String / StringBuffer / StringBuilder)
java.lang.Iterable (Collections, either explicitly or with for Blah blah : List<Blah>)
java.lang.Readable (Readers)
java.io.Closeable (Streams)
java.io.Flushable (Streams)
java.util.Collection (Collections)
java.util.Deque (Collections)
java.util.List (Collections)
java.util.Map (Collections)
java.util.Set (Collections)
Interfaces that are most likely to blow up in your face:
java.lang.Cloneable
Edit: Whoops, Throwable’s not an interface.
Usually, it’s better to write a Copy Constructor rather than use a clone() method.
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