fixed_queue.mirah

# A Queue of fixed size, using an array for storage

class FixedQueue

  attr_reader added:int, removed:int

  def initialize(capacity:int)
    @added = 0
    @removed = 0
    @capacity = capacity
    @data = Object[capacity]
  end

  def isEmpty?
    (@removed >= @added)
  end

  def isFull?
    (@added >= @removed + @capacity)
  end

  def add(obj:Object)
    if isFull?
      false
    else
      @data[@added % @capacity] = obj
      @added += 1
      true
    end
  end

  def remove
    if isEmpty?
      nil
    else
      @removed += 1
      @data[(@removed - 1) % @capacity]
    end
  end

  def to_s
    out = ""
    @removed.upto(@added - 1) do |i|
      out +=  ", #{@data[i % @capacity]}"
    end
    "{" + out.substring(out.length > 0 ? 1 : 0) + " }"
  end

end

fixed_queue_spec.rb

# rvm jruby
# rspec -fs spec/fixed_queue_spec.rb

require 'java'
import 'cis.FixedQueue'

describe FixedQueue, 'once queue is created' do
  before(:each) do
    @capacity = 9
    @queue = FixedQueue.new(@capacity)
  end

  context 'when empty' do
    it 'should respond as empty' do
      @queue.should be_empty
    end

    it 'should not respond as full' do
      @queue.should_not be_full
    end

    it 'should return null on remove()' do
      @queue.remove.should be_false
    end

    it 'should report none added() or removed()' do
      @queue.added.should == 0
      @queue.removed.should == 0
    end

    it 'should provide string representation' do
      @queue.to_s.should eq "{ }"
    end
  end

  context 'when items have been added' do

    context 'when under capacity' do
      before(:each) do
        %w{foo bar baz}.each {|s| @queue.add(s)}
      end

      it 'should not report empty' do
        @queue.should_not be_empty
      end

      it 'should respond true on add(obj)' do
        @queue.should be_add('zippy')
      end

      it 'should report number added() and removed()' do
        @queue.added.should == 3
        @queue.removed.should == 0
      end

      it 'should provide string representation' do
        @queue.to_s.should eq "{ foo, bar, baz }"
      end
    end

    context 'when at capacity' do
      before(:each) do
        @capacity.times {@queue.add('foo')}
      end

      it 'should respond as full' do
        @queue.should be_full
      end

      it 'should respond false on add(obj)' do
        @capacity.times {@queue.add('foo')}
        @queue.should_not be_add('foo')
      end
    end

    context 'when beyond initial capacity after remove()' do
      before(:each) do
        @capacity.times {@queue.add('foo')}
        @capacity.times {@queue.remove}
        %w{foo bar baz}.each {|s| @queue.add(s)}
      end

      it 'should report number added() and removed()' do
        @queue.added.should == @capacity + 3
        @queue.removed.should ==  @capacity
      end

      it 'should provide string representation' do
        @queue.to_s.should eq "{ foo, bar, baz }"
      end
    end

  end

  context 'when items are removed' do
    before(:each) do
      %w{foo bar baz}.each {|s| @queue.add(s)}
    end

    it 'should return first Object added: (FIFO)' do
      @queue.remove.should eq "foo"
      @queue.remove.should eq "bar"
      @queue.to_s.should eq "{ baz }"
    end

    it 'should still return null on remove() once empty' do
      3.times {@queue.remove}
      @queue.remove.should be_false
    end
  end
end


__END__

$ rvm jruby
$ rspec -fs spec/fixed_queue_spec.rb

Java::Cis::FixedQueue once queue is created
  when empty
    should respond as empty
    should not respond as full
    should return null on remove()
    should report none added() or removed()
    should provide string representation
  when items have been added
    when under capacity
      should not report empty
      should respond true on add(obj)
      should report number added() and removed()
      should provide string representation
    when at capacity
      should respond as full
      should respond false on add(obj)
    when beyond initial capacity after remove()
      should report number added() and removed()
      should provide string representation
  when items are removed
    should return first Object added: (FIFO)
    should still return null on remove() once empty

Finished in 0.165 seconds
15 examples, 0 failures

FixedQueue.java

// A Queue of fixed size, using an array for storage

package cis;

public class FixedQueue {

  private int added = 0;
  private int removed = 0;
  private int capacity;
  private Object[] data;

  public int added()   { return added; }
  public int removed() { return removed; }

  public FixedQueue(int capacity) {
    this.capacity = capacity;
    this.data = new Object[capacity];
  }

  public boolean isEmpty() {
    return (removed >= added);
  }

  public boolean isFull() {
    return (added >= removed + capacity);
  }

  public boolean add(Object obj) {
    if (isFull()) {
      return false;
    } else {
      data[added % capacity] = obj;
      added++;
      return true;
    }
  }

  public Object remove() {
    if (isEmpty()) {
      return null;
    } else {
      removed++;
      return data[(removed - 1) % capacity];
    }
  }
  
  public String toString() {
    StringBuilder sb = new StringBuilder();
    for (int i = removed; i < added; i++) {
      sb.append(", " + data[i % capacity]);
    }
    return "{" + sb.substring(sb.length() > 0 ? 1 : 0) + " }";
  }

}