San Jose State University | CS 151 - OO Design Section 5 | Fall 2016

Homework 4

Put all work into a directory hw4 of your Git project and push it once a day. Don't put any code into packages. Don't put any code into a src subdirectory.

You are given an interface NumberSequence that represents a finite or infinite sequence of integers:

public interface NumberSequence
{
   long next();
   default boolean hasNext() { return true; }
}

Provide a class SquareSequence that implements this interface, so that successive calls to the next method yield the squares of integers 0, 1, 4, 9, 16, 25, 36, ...
Add a method of(long... args) to the NumberSequence interface so that one can construct an instance of a finite sequence by specifying the elements, like this:
```
NumberSequence seq = NumberSequence.of(1, 1, 2, 3, 5, 8, 13, 21);
```
In the NumberSequence interface, provide a default method double average(int n) that computes the average of the first n elements (or all elements if there are fewer) and a method double average() that computes the average of all elements (which should only be called on a finite sequence). Sample usage:
```
double avg = new SquareSequence().average(5);
  // yields (0 + 1 + 4 + 9 + 16) * 1.0 / 5
avg = NumberSequence.of(1, 1, 2, 3, 5, 8, 13, 21).average();
  // yields the average of all elements
```
In the NumberSequence interface, provide a default method toArray that yields an array of the first n elements of the sequence:
```
long[] array = someSequence.toArray(n);
```
If there are fewer than n elements, return a shorter array holding all of them.
In the NumberSequence interface, provide a method default NumberSequence filter(LongPredicate p) that yields a sequence of numbers fulfilling the predicate. For example:
```
NumberSequence oddSquares = new SquareSequence().filter(n -> n % 2 != 0);
   // the sequence with elements 1, 9, 25, 49, ...
```
In the NumberSequence interface, produce a static method iterate(long seed, LongUnaryOperator f) that produces an infinite stream of values seed, f(seed), f(f(seed)), and so on. For example,
```
NumberSequence.iterate(0, x -> x + 1)
```

In the NumberSequence interface, produce a static method random(long seed) that creates random numbers, using a linear congruential generator with m = 2³¹, a = 1103515245 and c = 12345. Use iterate and a lambda expression.

Provide javadoc for the interface and all methods.

Here is a JUnit test class.