## Problema

1. Considere a tabela da 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.
2. 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).
3. 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.

# Solução

## 1. Tabela comparável

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();
}
}
```

## 2. Comparadores de Máximo e Comprimento

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;
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)

## Exemplo de Aplicação

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)

}

}
```