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7/31/2019 Collections Print

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Java Collections

Java Collections

Object-oriented programming

Inf1 :: 2005

Object-oriented programming Java Collections
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2/20

Java Collections

Collections

Data structures like the ones we discussed in the previouslectures are so important that the Java library provided ageneric implementation

Package java.util

The collections framework is a perfect example ofpolymorphism, interfaces and object-oriented design

There is a basic interface (Collection) that all classes injava.util implementBehaviours are implemented in a variety of ways

We will deal with lists, sets, iterators and trees

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3/20

Java Collections

The class/interface hierarchy

Collection

boolean isEmpty ()

boolean add/remove (Object o)boolean add/removeAll (Collection c)

void clear ()

boolean contains (Object o)

boolean containsAll (Collection c)

Iterator iterator ()

int size ()

Object [] toArray ()

List

Object get (int index)

Object set (int index, Object o)

void add (int index, Object o)void addAll (int index, Collection c)

Object remove (int index)

int indexOf (Object o)

int lastIndexOf (Object o)

ListIterator listIterator ()

ListIterator listIterator (int index)

List subList (int start, int end)

AbstractList

void removeRange (int start, int end)

LinkedList

Object getFirst ()

Object getLast ()

void addFirst (Object o)

void addLast (Object o)

Object removeFirst ()

Object removeLast ()

AbstractSequentialList

ArrayList

void ensureCapacity (int min)

void trimToSize ()

Iterator

boolean hasNext ()

Object next ()

void remove ()

ListIterator

boolean hasPrevious ()

Object previous ()

int nextIndex ()

int previousIndex ()

Comparator

int compare (Object o1, Object o2)

Set

SortedSet

Comparator comparator ()

Object first ()

Object last ()

SortedSet headSet (Object to)

SortedSet tailSet (Object from)

SortedSet subset (Object from, Object to)

TreeSet

AbstractSet

HashSet

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4/20

Java Collections

In more detail

Collections are either Lists or Sets

Lists areSequentialPossibly with duplicate valuesUnordered with respect to the values they store

Sets are

Unordered with respect to the valuesWithout any duplicate values

SortedSets are

Ordered (with respect to their values) Sets

Iterators areA way oftraversing all values in a Collection

ListIterators are

Special Iterators that allow one to traverse sequentialCollections like Lists


ll
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5/20

Java Collections

Using a List

import java.util.*;

public class ListTest {

private static final String colors[] = { "red", "white", "blue",

"green", "gray", "orange", "tan", "white", "cyan","peach", "gray", "orange" };

public ListTest () {List list = new ArrayList();

for (int i = 0; i < colors.length; i++)list.add(colors[i]);

System.out.print("\nList: ");

printList(list);

System.out.print("\nReversed List: ");

printReversedList(list);

System.out.print("\nList from 5, forward: ");printListFromIndex(5, list);

System.out.print("\nList from 5, backward: ");

printReversedListFromIndex(5, list);

}

import

everything from thejava.util package (the

collections framework)

List interface

make the reference aim at aclass that implements theinterface (ArrayList)

polymorphism

ArrayLists implementation

of add() will be called;add() is a Collection

method and List extendsCollection


J C ll ti
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6/20

Java Collections

Traversing a List with an Iterator

public voidprintList (List l) {

Iterator iter = l.iterator();

while (iter.hasNext())System.out.print(iter.next() + " ");

System.out.println();

}

public voidprintReversedList (List l) {

ListIterator iter = l.listIterator(l.size());

while (iter.hasPrevious())

System.out.print(iter.previous() + " ");


}

iterator

declare an Iterator over the

List, i.e., obtain a sequential handle

over the Lists data; iterator()

returns a ListIterator, which is

an Iterator

forward scankeep scanning forward, as

long as the Iterator

says there are more

elements

list iterator

declare a ListIterator over

the List, since we want the

extra functionality of scanning

from a specific point

backward scan

keep scanning backwards, aslong as the ListIterator

says there are more elements


J C ll ti


7/20

Java Collections

Using a List results

import java.util.*;

public class ListTest {



public ListTest () {

List list = new ArrayList();

for (int i = 0; i < colors.length; i++)

list.add(colors[i]);

System.out.print("\nList: ");printList(list);

System.out.print("\nReversed List: ");

printReversedList(list);

System.out.print("\nList from 5, forward: ");

printListFromIndex(5, list);

System.out.print("\nList from 5, backward: ");

printReversedListFromIndex(5, list);

}

List: red white blue green gray orange tan white cyan peach gray orange

Reversed List: orange gray peach cyan white tan orange gray green blue white red

List from 5, forward: orange tan white cyan peach gray orange

List from 5, backward: gray green blue white red


Java Collections


8/20

Java Collections

Using a Set

import java.util.*;

public class SetTest {


"green", "gray", "orange", "tan", "white", "cyan",

"peach", "gray", "orange" };

public SetTest () {



System.out.print("\nArrayList: ");printCollection(list);

Set hashSet = new HashSet(list);

System.out.print("\nHashSet: ");

printCollection(hashSet);}

import

java.util.* imports

the Collections framework

reference to concrete classassign a List (interface) reference

to anArrayListconcrete class

(that implements the interface)

create a set from a list

use a Set (interface) reference to a

HashSetconcrete class (that

implements the interface); use a list

as the input collection


Java Collections
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9/20

Java Collections

Traversing a Set

public voidprintCollection (Collection c) {

Iterator iter = c.iterator();

while (iter.hasNext())

System.out.print(iter.next() + " ");


}

Collection as parameter

this will work for both

Lists and Sets since they

both extendCollection


Java Collections
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10/20

Java Collections

Using s Set results

import java.util.*;

public class SetTest {



public SetTest () {List list = new ArrayList();


System.out.print("\nArrayList: ");

printCollection(list);

Set hashSet = new HashSet(list);

System.out.print("\nHashSet: ");

printCollection(hashSet);}

ArrayList: red white blue green gray orange tan white cyan peach gray orange

HashSet: red cyan white tan gray green orange blue peach


Java Collections
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11/20

Java Collections

Using a SortedSet

import java.util.*;

public class SortedSetTest {

private static final String names[] = { "yellow", "green","black", "tan", "grey", "white","orange", "red", "green" };

public SortedSetTest () {SortedSet set = new TreeSet ();

for (int i = 0; i < names.length; i++)set.add(names[i]);

System.out.print("\nset: ");printSet(set);

System.out.print("\nheadSet(\"orange\"): ");printSet(set.headSet("orange"));

System.out.print("\ntailSet(\"orange\"): ");printSet(set.tailSet("orange"));

System.out.print("\nheadSet(\"foo\"): ");printSet(set.headSet("foo"));

System.out.print("\ntailSet(\"foo\"): ");printSet(set.tailSet("foo"));

System.out.print("\nfirst: ");System.out.println(set.first());

System.out.print("\nlast: ");System.out.println(set.last());

}

polymorphism

TreeSetimplementsSortedSet

SortedSetbehaviour

the methods called are

SortedSetmethods, but

TreeSets implementations

will be called


Java Collections
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12/20

J

Traversing a SortedSet through an Iterator

public voidprintSet (SortedSet set) {Iterator iter = set.iterator();

while (iter.hasNext())

System.out.print(iter.next() + " ");


}

SortedSetreference

though a TreeSet

instance will bepassed as

aparameter by the caller

Collectionbehaviour

a SortedSetis still a

Collectionso we canhave an Iterator over it


Java Collections
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13/20

J

Using s SortedSet resultsimport java.util.*;

public class SortedSetTest {

private static final String names[] = { "yellow", "green",

"black", "tan", "grey", "white","orange", "red", "green" };

public SortedSetTest () {SortedSet set = new TreeSet ();

for (int i = 0; i < names.length; i++)set.add(names[i]);

System.out.print("\nset: ");printSet(set);

System.out.print("\nheadSet(\"orange\"): ");printSet(set.headSet("orange"));

System.out.print("\ntailSet(\"orange\"): ");printSet(set.tailSet("orange"));

System.out.print("\nheadSet(\"foo\"): ");printSet(set.headSet("foo"));

System.out.print("\ntailSet(\"foo\"): ");printSet(set.tailSet("foo"));

System.out.print("\nfirst: ");

System.out.println(set.first());

System.out.print("\nlast: ");System.out.println(set.last());

}

set: black green grey orange red tan white yellowheadSet("orange"): black green greytailSet("orange"): orange red tan white yellowheadSet("foo"): blacktailSet("foo"): green grey orange red tan white yellowfirst: black

last: yellow


Java Collections
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14/20

Classes Arrays and Collections

Provide generic implementations of certain functions

Static method calls to invoke desired behaviour

Arrays.sort(array , value)Arrays.binarySearch(array , value)Collections.sort(Collection c)

Collections.binarySearch(Collection c , Object o)

We will focus on Collections


Java Collections


15/20

Sorting and searching a List

Carried out with the aid of an object that implements theComparator interface

Main comparison method is: int compare (Object o1,Object o2)

Ifo1 < o2, then return a negative integerIfo1 == o2, then return zeroIfo1 > o2, then return a positive integer


Java Collections


16/20

A Time classimport java.text.DecimalFormat;

public class Time {

private int hour;

private int minute;

private int second;

public Time () { this(0, 0, 0); }

public Time (int h) { this(h, 0, 0); }

public Time (int h, int m) { this(h, m, 0); }

public Time (int h, int m, int s) {

setTime(h, m, s);

}

public voidsetTime (int h, int m, int s) {setHour(h);

setMinute(m);

setSecond(s);

}

public voidsetHour (int h) { hour = ((h >= 0 || h < 24) ? h : 0); }

public voidsetMinute (int m) { minute = ((m >= 0 || m < 60) ? m : 0); }

public voidsetSecond (int s) { second = ((s >= 0 || s < 60) ? s : 0); }

public int getHour () { return hour; }

public int getMinute () { return minute; }

public int getSecond () { return second; }

public String toString () {

DecimalFormat twoDigits = new DecimalFormat("00");

return twoDigits.format(hour) + ":"

+ twoDigits.format(minute) + ":" + twoDigits.format(second);

}

}


Java Collections


17/20

A TimeComparator class

import java.util.Comparator;

public class TimeComparator implements Comparator {

public TimeComparator () {}

public int compare (Object o1, Object o2) {Time t1 = (Time) o1;

Time t2 = (Time) o2;

int comp = (t1.getHour() - t2.getHour());

if (comp != 0) return comp;

comp = (t1.getMinute() - t2.getMinute());

if (comp != 0) return comp;

comp = (t1.getSecond() - t2.getSecond());

return comp;

}

}

import

simply import

the necessaryinterface

implementation

specify which interface is

implemented and provide animplementation for the methods

of the interface

cast

TimeComparator can only

handle Timeobjects; cast the

parameters to Time (anything

else will be a runtime error)

comparison

make the comparison, at all

times abiding by the

semantics of the interface


Java Collections
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18/20

Sorting a List ofTime objects

import java.util.*;

public class CollectionSortTest {

public static voidmain (String args []) {


list.add(new Time( 6, 24, 34));

list.add(new Time(18, 14, 5));


list.add(new Time(12, 07, 58));


System.out.print("unsorted list is: ");

System.out.println(list);

Collections.sort(list, new TimeComparator());

System.out.print("sorted list is: ");

System.out.println(list);

}

}

static call

Collections.sort()is a static method

TimeComparator

passed as the argument

to sort(); becomes the

sorting criterion

unsorted list is: [06:24:34, 18:14:05, 08:05:00, 12:07:58, 06:14:22]

sorted list is: [06:14:22, 06:24:34, 08:05:00, 12:07:58, 18:14:05]


Java Collections
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19/20

Sorting and searching a List ofString objects

import java.util.*;

public class CollectionSearchTest {


"green", "gray", "orange", "tan", "white", "cyan",

"peach", "gray", "orange" };

public staticvoidmain (String args []) {


for (int i = 0; i < colors.length; i++)

list.add(colors[i]);

System.out.println("unsorted list: " + list);

Collections.sort(list);

System.out.println("sorted list: " + list);

int p = Collections.binarySearch(list, "gray");

System.out.println("gray first appears in position: " + p);

p = Collections.binarySearch(list, "maroon");

System.out.println("maroon first appears in position: " + p);

}

}

no need for aComparator

the class of the objectsinserted

in the list (String), already

implements the Comparator

interface

unsorted list: [red, white, blue, green, gray, orange, tan, white, cyan, peach, gray, orange]

sorted list: [blue, cyan, gray, gray, green, orange, orange, peach, red, tan, white, white]

gray first appears in position: 2

maroon first appears in position: -6

Collections.binarySearch()

pass a list and the object were

looking for and were done!


Java Collections
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20/20

Things to do

To do

Read Deitel & Deitel, Sections 22.1, 22.2, 22.4, 22.5, 22.7

Become accustomed with the Java Collections framework

Spend some time thinking on the differences between thevarious interfaces and classes


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