Chapter 16

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Chapter 16

Collections and Iterators

This activity contains 15 questions.

A ListIterator is an example of an Iterator. What additional methods does the ListIterator interface provide?

It has the ability to set and add elements to the collectionIt has a previous method and a next methodIt has a next method and the ability to set and add elements to the collectionIt has a previous method and the ability to set and add elements to the collection

Comparing List and Set Collections and the order of elements within...

Both Lists and Sets impose a specific orderSets impose a specific order; Lists do notNeither Lists nor Sets impose a specific orderLists impose a specific order; Sets do not

Comparing the List and Set Collections...

Both Lists and Sets may contain duplicated elementsNeither Lists nor Sets may contain duplicated elementsLists may contain duplicated elements, while Lists may notSets may contain duplicated elements, while Lists may not

Considering the Collections classes, would it be possible to implement the containsAll method using the contains method (and possibly others)?

No. This is because you have no way to determine whether the same number and kind of elements are in two CollectionsYes. But you'd need to ensure that the equals method was appropriately definedNo. This is because you'd not be able to compare the elements within each Collection if they're not of exactly the same type without causing an exception to be thrownNo. This is because you'd destroy one or both of the Collections during the execution of such a method if you created it "from scratch"

In the ListIterator Collection the next and previous methods return references. What might be the advantage of this fact?

The List data becomes "publicly available" via the reference, thus ensuring privacy leaksThere is really are no particular advantages - just disadvantagesThe List data is immutable, so it isn't really much of an advantageThe List data can be modified in place

Say you need an array that has the ability to be extended and contracted during execution. You decide to use one of the Collection classes in lieu of your array. What difficulties might you encounter?

You can't store primitive data directly into a CollectionThere would be no special difficulties - just different exceptions might be thrown during executionYou'd not be able to use [ ] to indicate subscripting, but otherwise would encounter no troubleYou couldn't subscript the same way, and you'd have difficulties storing primitive data

What does this code print?

import java.util.HashSet;
import java.util.Iterator;

public class Iter {

	Iter() {
		HashSet s = new HashSet();
		for (int i=1; i<7; i++)
			for (int j=0; j

Nothing is printed because an exception is thrown during execution763

What does this code print?

import java.util.Vector;
import java.util.Iterator;

public class Vect {

	Vect() {
		Vector v = new Vector();
		for (int i=0; i<4; i++)
			v.add(i, "st" + 4*i);

		Iterator i = v.iterator();
		int n = 0;
		while (i.hasNext()) {
			n += ((String)i.next()).
								   length();
		}
		System.out.println(n);
	}

	public static void main(String[] args) {
		new Vect();
	}

}

12st1213st13

What does this program print?

import java.util.List;
import java.util.ArrayList;
import java.util.ListIterator;

public class Iter {

	Iter() {
		ArrayList lst = new ArrayList();
		for (int i=1; i<=7; i++)
			lst.add(new Integer(i));
		lst = massage(lst);
		lst = massage(lst);
		System.out.println(lst.get(3));
	}

	private ArrayList massage(List lst) {
		ListIterator i = lst.listIterator();
		ArrayList lst2 = new ArrayList();
		while (i.hasNext()) {
			Object obj = i.next();
			lst2.add(0, obj);
		}
		return lst2;
	}

	public static void main(String[] args) {
		new Iter();
	}

}

3Nothing is printed because an exception is thrown during execution54

What is printed by the following code?

import java.util.Vector;

public class Vect {

	Vect() {
		Vector v = new Vector(4);
		for (int i=1; i<5; i++)
			v.add("st" + i);
		System.out.println(v.get(1));
	}

	public static void main(String[] args) {
		new Vect();
	}

}

st3Nothing. There's a syntax error and the code doesn't compile or executest2st1

What is printed by this code?

import java.util.Vector;

public class Vect {

	Vect() {
		Vector v = new Vector(10);
		for (int i=0; i<10; i++)
			v.add(null);
		for (int i=0; i<10; i+=2) {
			v.set(i, "st" + i);
			v.set(i+1, "uv" + (i+1));
		}
		System.out.println(
			(String) v.get(4) + v.get(5));
	}

	public static void main(String[] args) {
		new Vect();
	}

}

st4uv5st5uv6uv4st5st3uv4

What is printed by this code?

import java.util.Vector;

public class Vect {

	Vect() {
		Vector v = new Vector();
		for (int i=0; i<10; i++)
			v.add(0, "st" + i);

		System.out.println(
			(String) v.get(4) + v.get(5));
	}

	public static void main(String[] args) {
		new Vect();
	}

}

st5st4st4st5st5st6st6st5

What is printed by this code?

import java.util.Vector;

public class Vect {

	Vect() {
		int[] a = { 3, 1, 4, 1, 
					5, 9, 2, 6 };
		Vector v = new Vector();
		for (int i=0; i

69112543629514133141592662951143

What is printed by this code?

import java.util.Vector;
import java.util.Iterator;

public class Vect {

	Vect() {
		Vector v = new Vector();
		for (int i=0; i<5; i++)
			v.add(i, "st" + 4*i);

		Iterator i = v.iterator();
		int n = 0;
		boolean bFlag = false;
		while (i.hasNext()) {
			if (bFlag)
				v.set(v.indexOf(i.next(),
							0),
							"uv" + --n);
			else
				i.next();
			bFlag = ! bFlag;
		}
		System.out.println(
				(String) v.get(2) +
 								  v.get(3));
	}

	public static void main(String[] args) {
		new Vect();
	}

}

uv-2st8st8uv-2uv-1st8Nothing. An exception is thrown

What is the principal advantage (property) of the TreeSet class?

Rapid retrieval of data, guaranteed to have no duplicatesA TreeSet has a root which you may utilize if you need to They provide an ordering while normal sets do notThey provide mechanisms for preorder, inorder and postorder traversal

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Chapter 16

A ListIterator is an example of an Iterator. What additional methods does the ListIterator interface provide?

Comparing List and Set Collections and the order of elements within...

Comparing the List and Set Collections...

Considering the Collections classes, would it be possible to implement the containsAll method using the contains method (and possibly others)?

In the ListIterator Collection the next and previous methods return references. What might be the advantage of this fact?

Say you need an array that has the ability to be extended and contracted during execution. You decide to use one of the Collection classes in lieu of your array. What difficulties might you encounter?

What is printed by the following code?
import java.util.Vector; public class Vect { Vect() { Vector v = new Vector(4); for (int i=1; i<5; i++) v.add("st" + i); System.out.println(v.get(1)); } public static void main(String[] args) { new Vect(); } }

What is printed by this code?
import java.util.Vector; public class Vect { Vect() { Vector v = new Vector(); for (int i=0; i<10; i++) v.add(0, "st" + i); System.out.println( (String) v.get(4) + v.get(5)); } public static void main(String[] args) { new Vect(); } }

What is the principal advantage (property) of the TreeSet class?

Chapter 16

A ListIterator is an example of an Iterator. What additional methods does the ListIterator interface provide?

Comparing List and Set Collections and the order of elements within...

Comparing the List and Set Collections...

Considering the Collections classes, would it be possible to implement the containsAll method using the contains method (and possibly others)?

In the ListIterator Collection the next and previous methods return references. What might be the advantage of this fact?

Say you need an array that has the ability to be extended and contracted during execution. You decide to use one of the Collection classes in lieu of your array. What difficulties might you encounter?

What is printed by the following code? import java.util.Vector; public class Vect { Vect() { Vector v = new Vector(4); for (int i=1; i<5; i++) v.add("st" + i); System.out.println(v.get(1)); } public static void main(String[] args) { new Vect(); } }

What is printed by this code? import java.util.Vector; public class Vect { Vect() { Vector v = new Vector(); for (int i=0; i<10; i++) v.add(0, "st" + i); System.out.println( (String) v.get(4) + v.get(5)); } public static void main(String[] args) { new Vect(); } }

What is the principal advantage (property) of the TreeSet class?

What is printed by the following code?
import java.util.Vector; public class Vect { Vect() { Vector v = new Vector(4); for (int i=1; i<5; i++) v.add("st" + i); System.out.println(v.get(1)); } public static void main(String[] args) { new Vect(); } }

What is printed by this code?
import java.util.Vector; public class Vect { Vect() { Vector v = new Vector(); for (int i=0; i<10; i++) v.add(0, "st" + i); System.out.println( (String) v.get(4) + v.get(5)); } public static void main(String[] args) { new Vect(); } }