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Listing 4 . Get an Iterator object.
Iterator iter = ref.iterator();

The call to the iterator method on any Collection object returns an instance of a class that implements the Iterator interface. The Iterator object can be used to traverse the collection, gaining access to each element in order. (The concept of in order means different things for different kinds of collections. For a collection instantiated fromthe TreeSet class, in order means in ascending order.)

Again, don't know, don't care

Again, the author of the method that uses the Collection object doesn't need to know or care about the internal implementation of thecollection, or the implementation of the methods of the Iterator object. They simply do what they do, and can be used for their intended purpose.

An Iterator object acts as a doorkeeper

The Iterator interface declares three methods:

  • hasNext()
  • next()
  • remove()

You might say that an Iterator object acts as a doorkeeper for the collection object that it represents, providing access to the contents of thecollection in a very specific manner.

Traverse the collection

The code fragment in Listing 5 below shows how the first two of the above methods can be used to

  • Traverse the collection, accessing each of the object's elements in succession.
  • Display the value encapsulated in the object referred to by each element.

As mentioned earlier, when the collection is an object instantiated from the TreeSet class, access to the elements is provided in ascending order.

Listing 5 . Traverse the collection.
while(iter.hasNext()){ System.out.print(iter.next());}//end while loop

Four elements with no duplicates

At this point, the TreeSet object contains four elements, with no duplicates. Each of the elements is a reference to an object of type Integer . The code in the loop in Listing 5 causes each of those elements to be accessed and displayed in ascending order. This causes the following text to appear on thescreen:

1234

An editorial opinion

In my opinion, this is the kind of knowledge that a computer science student in a modern data structures course should be learning. This is a far departurefrom courses of the past where CS2 students were required to memorize the intricate details of how to implement various data structures.

What kind of knowledge is needed?

Does an architect need to understand the detailed inner workings of an air conditioning compressor to design a cooling system into a building? Ofcourse not!

However, the architect does need to know the tradeoffs among the available cooling systems in terms of initial cost, operating cost, size, efficiency, etc.

Does an audio technician need to understand the detailed inner workings of an electronic audio equalizer in order to construct an integrated audio system?Absolutely not! If that were a requirement, there would likely be very few audio systems in existence.

However, the audio technician does need to understand the tradeoffs among the various available audio equalizers.

The same concept applies to software design

Does an OOP software designer need to know the detailed inner workings of the various kinds of collection objects in order to use them effectively? No!

Questions & Answers

A golfer on a fairway is 70 m away from the green, which sits below the level of the fairway by 20 m. If the golfer hits the ball at an angle of 40° with an initial speed of 20 m/s, how close to the green does she come?
Aislinn Reply
cm
tijani
what is titration
John Reply
what is physics
Siyaka Reply
A mouse of mass 200 g falls 100 m down a vertical mine shaft and lands at the bottom with a speed of 8.0 m/s. During its fall, how much work is done on the mouse by air resistance
Jude Reply
Can you compute that for me. Ty
Jude
what is the dimension formula of energy?
David Reply
what is viscosity?
David
what is inorganic
emma Reply
what is chemistry
Youesf Reply
what is inorganic
emma
Chemistry is a branch of science that deals with the study of matter,it composition,it structure and the changes it undergoes
Adjei
please, I'm a physics student and I need help in physics
Adjanou
chemistry could also be understood like the sexual attraction/repulsion of the male and female elements. the reaction varies depending on the energy differences of each given gender. + masculine -female.
Pedro
A ball is thrown straight up.it passes a 2.0m high window 7.50 m off the ground on it path up and takes 1.30 s to go past the window.what was the ball initial velocity
Krampah Reply
2. A sled plus passenger with total mass 50 kg is pulled 20 m across the snow (0.20) at constant velocity by a force directed 25° above the horizontal. Calculate (a) the work of the applied force, (b) the work of friction, and (c) the total work.
Sahid Reply
you have been hired as an espert witness in a court case involving an automobile accident. the accident involved car A of mass 1500kg which crashed into stationary car B of mass 1100kg. the driver of car A applied his brakes 15 m before he skidded and crashed into car B. after the collision, car A s
Samuel Reply
can someone explain to me, an ignorant high school student, why the trend of the graph doesn't follow the fact that the higher frequency a sound wave is, the more power it is, hence, making me think the phons output would follow this general trend?
Joseph Reply
Nevermind i just realied that the graph is the phons output for a person with normal hearing and not just the phons output of the sound waves power, I should read the entire thing next time
Joseph
Follow up question, does anyone know where I can find a graph that accuretly depicts the actual relative "power" output of sound over its frequency instead of just humans hearing
Joseph
"Generation of electrical energy from sound energy | IEEE Conference Publication | IEEE Xplore" ***ieeexplore.ieee.org/document/7150687?reload=true
Ryan
what's motion
Maurice Reply
what are the types of wave
Maurice
answer
Magreth
progressive wave
Magreth
hello friend how are you
Muhammad Reply
fine, how about you?
Mohammed
hi
Mujahid
A string is 3.00 m long with a mass of 5.00 g. The string is held taut with a tension of 500.00 N applied to the string. A pulse is sent down the string. How long does it take the pulse to travel the 3.00 m of the string?
yasuo Reply
Who can show me the full solution in this problem?
Reofrir Reply
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Source:  OpenStax, Object-oriented programming (oop) with java. OpenStax CNX. Jun 29, 2016 Download for free at https://legacy.cnx.org/content/col11441/1.201
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