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== Problema == | == Problema == | ||
− | # Considere a tabela da Aula | + | # Considere a tabela da [[Polimorfismo, Interfaces, Classes Abstractas/Exercício 02: Tabelas e Predicados|Aula Prática 05]]. Redefina a classe como sendo comparável. Diz-se que uma tabela é menor/igual/maior que outra quando se verificar a relação menor/igual/maior entre as somas dos elementos de cada uma. |
# Considere ainda o caso da alínea anterior. Defina agora dois comparadores (devem ser implementados como classes internas da tabela) que estabelecem as relações de comparação relativamente (i) aos máximos das tabelas e (ii) ao número de elementos (independentemente dos valores). | # Considere ainda o caso da alínea anterior. Defina agora dois comparadores (devem ser implementados como classes internas da tabela) que estabelecem as relações de comparação relativamente (i) aos máximos das tabelas e (ii) ao número de elementos (independentemente dos valores). | ||
# Considere agora, em lugar de tabelas de inteiros, que as tabelas contêm gatos (classe definida acima). Altere o código da alínea 2(i) para que funcione com as tabelas de gatos. | # Considere agora, em lugar de tabelas de inteiros, que as tabelas contêm gatos (classe definida acima). Altere o código da alínea 2(i) para que funcione com as tabelas de gatos. | ||
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= Solução = | = Solução = | ||
− | [[category: | + | == 1. Tabela comparável == |
− | [[category: | + | |
+ | Para este caso, é necessário definir a classe Table como implementando Comparable. | ||
+ | |||
+ | {{CollapsedCode|Ficheiro '''Table.java'''| | ||
+ | <source lang="java"> | ||
+ | /** | ||
+ | * A table holding a fixed number of integers. | ||
+ | * | ||
+ | * It is possible to verify certain predicates against the table's contents. | ||
+ | */ | ||
+ | public class Table implements Comparable<Table> { | ||
+ | |||
+ | /** | ||
+ | * Space for a fixed number of integers. | ||
+ | */ | ||
+ | int _vector[]; | ||
+ | |||
+ | /** | ||
+ | * @param nInts | ||
+ | * number of integers to store. | ||
+ | */ | ||
+ | public Table(int nInts) { | ||
+ | _vector = new int[nInts]; | ||
+ | } | ||
+ | |||
+ | /** | ||
+ | * FIXME: insert checks to ensure position is within range. | ||
+ | * | ||
+ | * @param position | ||
+ | * position to define | ||
+ | * @return value at position | ||
+ | */ | ||
+ | public int getValue(int position) { | ||
+ | return _vector[position]; | ||
+ | } | ||
+ | |||
+ | /** | ||
+ | * FIXME: insert checks to ensure position is within range. | ||
+ | * | ||
+ | * @param position | ||
+ | * position to define | ||
+ | * @param value | ||
+ | * value to set | ||
+ | */ | ||
+ | public void setValue(int position, int value) { | ||
+ | _vector[position] = value; | ||
+ | } | ||
+ | |||
+ | /** | ||
+ | * Set all positions to the same value. | ||
+ | * | ||
+ | * @param value | ||
+ | * value to set | ||
+ | */ | ||
+ | public void setAll(int value) { | ||
+ | for (int position = 0; position < _vector.length; position++) | ||
+ | _vector[position] = value; | ||
+ | } | ||
+ | |||
+ | /** | ||
+ | * @param predicate | ||
+ | * the predicate to validate. | ||
+ | * @return true, if the predicate is valid for at least one position; false, | ||
+ | * otherwise. | ||
+ | */ | ||
+ | public boolean contains(SelectionPredicate predicate) { | ||
+ | for (int position = 0; position < _vector.length; position++) | ||
+ | if (predicate.ok(_vector[position])) | ||
+ | return true; | ||
+ | return false; | ||
+ | } | ||
+ | |||
+ | /** | ||
+ | * This method makes it easy to get the sum of all elements. As with the | ||
+ | * predicate, this type of algorithm could also be provided from outside: | ||
+ | * instead of a selector, a collector would have to be provided. | ||
+ | * | ||
+ | * @return sum of all elements. | ||
+ | */ | ||
+ | public int getSum() { | ||
+ | int sum = 0; | ||
+ | for (int i : _vector) | ||
+ | sum += i; | ||
+ | return sum; | ||
+ | } | ||
+ | |||
+ | /** | ||
+ | * @see java.lang.Comparable#compareTo(java.lang.Object) | ||
+ | */ | ||
+ | @Override | ||
+ | public int compareTo(Table other) { | ||
+ | return getSum() - other.getSum(); | ||
+ | } | ||
+ | } | ||
+ | </source> | ||
+ | }} | ||
+ | |||
+ | == 2. Comparadores de Máximo e Comprimento == | ||
+ | |||
+ | {{CollapsedCode|Diagrama de classes| | ||
+ | (por lapso, o diagrama UML omite o método '''contains''', mas o resto está correcto) | ||
+ | [[Image:PO-Interfaces-Comparable-Comparator.png|600px]] | ||
+ | }} | ||
+ | |||
+ | Notar que as classes internas são static e que apenas estão contidas na classe Table por conveniência de ocultação de código. | ||
+ | |||
+ | {{CollapsedCode|Ficheiro '''Table.java'''| | ||
+ | <source lang="java"> | ||
+ | import java.util.Comparator; | ||
+ | |||
+ | /** | ||
+ | * A table holding a fixed number of integers. | ||
+ | * | ||
+ | * It is possible to verify certain predicates against the table's contents. | ||
+ | */ | ||
+ | public class Table implements Comparable<Table> { | ||
+ | |||
+ | /** | ||
+ | * A comparator for tables: based on maximum value. | ||
+ | * | ||
+ | * Use as: Table.MAX_COMPARATOR | ||
+ | */ | ||
+ | public final static Comparator<Table> MAX_COMPARATOR = new MaxComparator(); | ||
+ | |||
+ | /** | ||
+ | * A comparator for tables: based on length. | ||
+ | * | ||
+ | * Use as: Table.LENGTH_COMPARATOR | ||
+ | */ | ||
+ | public final static Comparator<Table> LENGTH_COMPARATOR = new LengthComparator(); | ||
+ | |||
+ | /** | ||
+ | * This is a private class implementing the comparator. | ||
+ | */ | ||
+ | private static class MaxComparator implements Comparator<Table> { | ||
+ | |||
+ | /** | ||
+ | * @see java.util.Comparator#compare(java.lang.Object, java.lang.Object) | ||
+ | */ | ||
+ | @Override | ||
+ | public int compare(Table table1, Table table2) { | ||
+ | return table1.getMax() - table2.getMax(); | ||
+ | } | ||
+ | |||
+ | } | ||
+ | |||
+ | /** | ||
+ | * This is a private class implementing the comparator. | ||
+ | */ | ||
+ | private static class LengthComparator implements Comparator<Table> { | ||
+ | |||
+ | /** | ||
+ | * @see java.util.Comparator#compare(java.lang.Object, java.lang.Object) | ||
+ | */ | ||
+ | @Override | ||
+ | public int compare(Table table1, Table table2) { | ||
+ | return table1.getLength() - table2.getLength(); | ||
+ | } | ||
+ | |||
+ | } | ||
+ | |||
+ | /** | ||
+ | * Space for a fixed number of integers. | ||
+ | */ | ||
+ | int _vector[]; | ||
+ | |||
+ | /** | ||
+ | * @param nInts | ||
+ | * number of integers to store. | ||
+ | */ | ||
+ | public Table(int nInts) { | ||
+ | _vector = new int[nInts]; | ||
+ | } | ||
+ | |||
+ | /** | ||
+ | * FIXME: insert checks to ensure position is within range. | ||
+ | * | ||
+ | * @param position | ||
+ | * position to define | ||
+ | * @return value at position | ||
+ | */ | ||
+ | public int getValue(int position) { | ||
+ | return _vector[position]; | ||
+ | } | ||
+ | |||
+ | /** | ||
+ | * FIXME: insert checks to ensure position is within range. | ||
+ | * | ||
+ | * @param position | ||
+ | * position to define | ||
+ | * @param value | ||
+ | * value to set | ||
+ | */ | ||
+ | public void setValue(int position, int value) { | ||
+ | _vector[position] = value; | ||
+ | } | ||
+ | |||
+ | /** | ||
+ | * Set all positions to the same value. | ||
+ | * | ||
+ | * @param value | ||
+ | * value to set | ||
+ | */ | ||
+ | public void setAll(int value) { | ||
+ | for (int position = 0; position < _vector.length; position++) | ||
+ | _vector[position] = value; | ||
+ | } | ||
+ | |||
+ | /** | ||
+ | * @param predicate | ||
+ | * the predicate to validate. | ||
+ | * @return true, if the predicate is valid for at least one position; false, | ||
+ | * otherwise. | ||
+ | */ | ||
+ | public boolean contains(SelectionPredicate predicate) { | ||
+ | for (int position = 0; position < _vector.length; position++) | ||
+ | if (predicate.ok(_vector[position])) | ||
+ | return true; | ||
+ | return false; | ||
+ | } | ||
+ | |||
+ | /** | ||
+ | * This method makes it easy to get the sum of all elements. As with the | ||
+ | * predicate, this type of algorithm could also be provided from outside: | ||
+ | * instead of a selector, a collector would have to be provided. | ||
+ | * | ||
+ | * @return sum of all elements. | ||
+ | */ | ||
+ | public int getSum() { | ||
+ | int sum = 0; | ||
+ | for (int i : _vector) | ||
+ | sum += i; | ||
+ | return sum; | ||
+ | } | ||
+ | |||
+ | /** | ||
+ | * This method makes it easy to get the maximum of all elements. As with the | ||
+ | * predicate, this type of algorithm could also be provided from outside: | ||
+ | * instead of a selector, a collector would have to be provided. | ||
+ | * | ||
+ | * @return maximum value in the table. | ||
+ | */ | ||
+ | public int getMax() { | ||
+ | int max = _vector[0]; | ||
+ | for (int i : _vector) | ||
+ | if (i > max) | ||
+ | max = i; | ||
+ | return max; | ||
+ | } | ||
+ | |||
+ | /** | ||
+ | * This method makes it easy to get the number of elements. As with the | ||
+ | * predicate, this type of algorithm could also be provided from outside: | ||
+ | * instead of a selector, a collector would have to be provided. | ||
+ | * | ||
+ | * In this case, we are not actually iterating, since it is much easier and | ||
+ | * efficient to access the length attribute. | ||
+ | * | ||
+ | * @return length of table. | ||
+ | */ | ||
+ | public int getLength() { | ||
+ | return _vector.length; | ||
+ | } | ||
+ | |||
+ | /** | ||
+ | * @see java.lang.Comparable#compareTo(java.lang.Object) | ||
+ | */ | ||
+ | @Override | ||
+ | public int compareTo(Table other) { | ||
+ | return getSum() - other.getSum(); | ||
+ | } | ||
+ | |||
+ | } | ||
+ | </source> | ||
+ | }} | ||
+ | |||
+ | == 3. Comparador de Tabelas de Gatos == | ||
+ | |||
+ | (a publicar) | ||
+ | |||
+ | == Exemplo de Aplicação == | ||
+ | |||
+ | {{CollapsedCode|Ficheiro '''Application.java'''| | ||
+ | <source lang="java"> | ||
+ | public class Application { | ||
+ | |||
+ | /** | ||
+ | * @param args | ||
+ | */ | ||
+ | public static void main(String[] args) { | ||
+ | Table t1 = new Table(3); // table with 3 integers | ||
+ | Table t2 = new Table(3); // table with 3 integers | ||
+ | |||
+ | t1.setAll(3); | ||
+ | t2.setAll(90); | ||
+ | |||
+ | System.out.println(t1.compareTo(t2)); // <0 | ||
+ | System.out.println(Table.MAX_COMPARATOR.compare(t1, t2)); // <0 | ||
+ | System.out.println(Table.MAX_COMPARATOR.compare(t1, t1)); // 0 | ||
+ | System.out.println(Table.MAX_COMPARATOR.compare(t2, t2)); // 0 | ||
+ | System.out.println(Table.MAX_COMPARATOR.compare(t2, t1)); // >0 | ||
+ | System.out.println(Table.LENGTH_COMPARATOR.compare(t1, t2)); // 0 (same length) | ||
+ | |||
+ | } | ||
+ | |||
+ | } | ||
+ | </source> | ||
+ | }} | ||
+ | |||
+ | [[category:Ensino]] | ||
+ | [[category:PO]] | ||
+ | [[category:PO Exemplos]] |
Para este caso, é necessário definir a classe Table como implementando Comparable.
Ficheiro Table.java |
---|
/**
* A table holding a fixed number of integers.
*
* It is possible to verify certain predicates against the table's contents.
*/
public class Table implements Comparable<Table> {
/**
* Space for a fixed number of integers.
*/
int _vector[];
/**
* @param nInts
* number of integers to store.
*/
public Table(int nInts) {
_vector = new int[nInts];
}
/**
* FIXME: insert checks to ensure position is within range.
*
* @param position
* position to define
* @return value at position
*/
public int getValue(int position) {
return _vector[position];
}
/**
* FIXME: insert checks to ensure position is within range.
*
* @param position
* position to define
* @param value
* value to set
*/
public void setValue(int position, int value) {
_vector[position] = value;
}
/**
* Set all positions to the same value.
*
* @param value
* value to set
*/
public void setAll(int value) {
for (int position = 0; position < _vector.length; position++)
_vector[position] = value;
}
/**
* @param predicate
* the predicate to validate.
* @return true, if the predicate is valid for at least one position; false,
* otherwise.
*/
public boolean contains(SelectionPredicate predicate) {
for (int position = 0; position < _vector.length; position++)
if (predicate.ok(_vector[position]))
return true;
return false;
}
/**
* This method makes it easy to get the sum of all elements. As with the
* predicate, this type of algorithm could also be provided from outside:
* instead of a selector, a collector would have to be provided.
*
* @return sum of all elements.
*/
public int getSum() {
int sum = 0;
for (int i : _vector)
sum += i;
return sum;
}
/**
* @see java.lang.Comparable#compareTo(java.lang.Object)
*/
@Override
public int compareTo(Table other) {
return getSum() - other.getSum();
}
}
|
Diagrama de classes |
---|
(por lapso, o diagrama UML omite o método contains, mas o resto está correcto) |
Notar que as classes internas são static e que apenas estão contidas na classe Table por conveniência de ocultação de código.
Ficheiro Table.java |
---|
import java.util.Comparator;
/**
* A table holding a fixed number of integers.
*
* It is possible to verify certain predicates against the table's contents.
*/
public class Table implements Comparable<Table> {
/**
* A comparator for tables: based on maximum value.
*
* Use as: Table.MAX_COMPARATOR
*/
public final static Comparator<Table> MAX_COMPARATOR = new MaxComparator();
/**
* A comparator for tables: based on length.
*
* Use as: Table.LENGTH_COMPARATOR
*/
public final static Comparator<Table> LENGTH_COMPARATOR = new LengthComparator();
/**
* This is a private class implementing the comparator.
*/
private static class MaxComparator implements Comparator<Table> {
/**
* @see java.util.Comparator#compare(java.lang.Object, java.lang.Object)
*/
@Override
public int compare(Table table1, Table table2) {
return table1.getMax() - table2.getMax();
}
}
/**
* This is a private class implementing the comparator.
*/
private static class LengthComparator implements Comparator<Table> {
/**
* @see java.util.Comparator#compare(java.lang.Object, java.lang.Object)
*/
@Override
public int compare(Table table1, Table table2) {
return table1.getLength() - table2.getLength();
}
}
/**
* Space for a fixed number of integers.
*/
int _vector[];
/**
* @param nInts
* number of integers to store.
*/
public Table(int nInts) {
_vector = new int[nInts];
}
/**
* FIXME: insert checks to ensure position is within range.
*
* @param position
* position to define
* @return value at position
*/
public int getValue(int position) {
return _vector[position];
}
/**
* FIXME: insert checks to ensure position is within range.
*
* @param position
* position to define
* @param value
* value to set
*/
public void setValue(int position, int value) {
_vector[position] = value;
}
/**
* Set all positions to the same value.
*
* @param value
* value to set
*/
public void setAll(int value) {
for (int position = 0; position < _vector.length; position++)
_vector[position] = value;
}
/**
* @param predicate
* the predicate to validate.
* @return true, if the predicate is valid for at least one position; false,
* otherwise.
*/
public boolean contains(SelectionPredicate predicate) {
for (int position = 0; position < _vector.length; position++)
if (predicate.ok(_vector[position]))
return true;
return false;
}
/**
* This method makes it easy to get the sum of all elements. As with the
* predicate, this type of algorithm could also be provided from outside:
* instead of a selector, a collector would have to be provided.
*
* @return sum of all elements.
*/
public int getSum() {
int sum = 0;
for (int i : _vector)
sum += i;
return sum;
}
/**
* This method makes it easy to get the maximum of all elements. As with the
* predicate, this type of algorithm could also be provided from outside:
* instead of a selector, a collector would have to be provided.
*
* @return maximum value in the table.
*/
public int getMax() {
int max = _vector[0];
for (int i : _vector)
if (i > max)
max = i;
return max;
}
/**
* This method makes it easy to get the number of elements. As with the
* predicate, this type of algorithm could also be provided from outside:
* instead of a selector, a collector would have to be provided.
*
* In this case, we are not actually iterating, since it is much easier and
* efficient to access the length attribute.
*
* @return length of table.
*/
public int getLength() {
return _vector.length;
}
/**
* @see java.lang.Comparable#compareTo(java.lang.Object)
*/
@Override
public int compareTo(Table other) {
return getSum() - other.getSum();
}
}
|
(a publicar)
Ficheiro Application.java |
---|
public class Application {
/**
* @param args
*/
public static void main(String[] args) {
Table t1 = new Table(3); // table with 3 integers
Table t2 = new Table(3); // table with 3 integers
t1.setAll(3);
t2.setAll(90);
System.out.println(t1.compareTo(t2)); // <0
System.out.println(Table.MAX_COMPARATOR.compare(t1, t2)); // <0
System.out.println(Table.MAX_COMPARATOR.compare(t1, t1)); // 0
System.out.println(Table.MAX_COMPARATOR.compare(t2, t2)); // 0
System.out.println(Table.MAX_COMPARATOR.compare(t2, t1)); // >0
System.out.println(Table.LENGTH_COMPARATOR.compare(t1, t2)); // 0 (same length)
}
}
|