多项选择题

Given a class whose instances， when found in a collection of objects， are sorted by using the compareTo（） method， which two statements are true？（）

A.The class implements java.lang.Comparable.
B.The class implements java.util.Comparator.
C.The interface used to implement sorting allows this class to define only one sort sequence.
D.The interface used to implement sorting allows this class to define many different sort sequences.

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多项选择题A programmer is developing a class Key， that will be used as a key in a standard java.util.HashMap. Which two methods should be overridden to assure that Key works correctly as a key？（）

A.public int hashCode（）
B.public void hashCode（）
C.public int compareTo（Object o）
D.public boolean equals（Object o）
E.public boolean compareTo（Key k）

单项选择题What is the appropriate definition of the hashCode method in class Person？（）

A.return super.hashCode（）；
B.return name.hashCode（） + age * 7；
C.return name.hashCode（） + comment.hashCode（） / 2；
D.return name.hashCode（） + comment.hashCode（） / 2- age * 3；

单项选择题Which statement is true about the set variable on line 12？（）

A.The set variable contains all six elements from the coll collection， and the order is guaranteed to be preserved.
B.The set variable contains only three elements from the coll collection， and the order is guaranteed to be preserved.
C.The set variable contains all six elements from the coll collection， but the order is NOT guaranteed to be preserved.
D.The set variable contains only three elements from the coll collection， but the order is NOT guaranteed to be preserved.

单项选择题Which code， inserted at line 4， guarantees that this program will output [1， 2]？（）

A.Set set = new TreeSet（）；
B.Set set = new HashSet（）；
C.Set set = new SortedSet（）；
D.List set = new SortedList（）；
E.Set set = new LinkedHashSet（）；

单项选择题A programmer must create a generic class MinMax and the type parameter of MinMax must implement Comparable. Which implementation of MinMax will compile？（）

A.A
B.B
C.C
D.D