Template Method in Java
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Watch Template Method's video tutorialBefore and after
BEFORE - The SortUp and SortDown classes are almost identical. There is a massive opportunity for reuse - if - the embedded comparison could be refactored.
class SortUp
{
///// Shell sort /////
public:
void sort(int v[], int n)
{
for (int g = n / 2; g > 0; g /= 2)
for (int i = g; i < n; i++)
for (int j = i - g; j >= 0; j -= g)
if (v[j] > v[j + g])
doSwap(v[j], v[j + g]);
}
private:
void doSwap(int &a, int &b)
{
int t = a;
a = b;
b = t;
}
};
class SortDown
{
public:
void sort(int v[], int n)
{
for (int g = n / 2; g > 0; g /= 2)
for (int i = g; i < n; i++)
for (int j = i - g; j >= 0; j -= g)
if (v[j] < v[j + g])
doSwap(v[j], v[j + g]);
}
private:
void doSwap(int &a, int &b)
{
int t = a;
a = b;
b = t;
}
};
int main(void)
{
const int NUM = 10;
int array[NUM];
srand((unsigned)time(0));
for (int i = 0; i < NUM; i++)
{
array[i] = rand() % 10+1;
cout << array[i] << ' ';
}
cout << '\n';
SortUp upObj;
upObj.sort(array, NUM);
for (int u = 0; u < NUM; u++)
cout << array[u] << ' ';
cout << '\n';
SortDown downObj;
downObj.sort(array, NUM);
for (int d = 0; d < NUM; d++)
cout << array[d] << ' ';
cout << '\n';
system("pause");
}
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AFTER - The common implementation has been moved to an abstract base class, and a "placeholder" has been defined to encapsulate the embedded comparison.
All that remains for the SortUp and SortDown classes is to implement that placeholder.
class AbstractSort
{
////// Shell sort //////
public:
void sort(int v[], int n)
{
for (int g = n / 2; g > 0; g /= 2)
for (int i = g; i < n; i++)
for (int j = i - g; j >= 0; j -= g)
if (needSwap(v[j], v[j + g]))
doSwap(v[j], v[j + g]);
}
private:
virtual int needSwap(int, int) = 0;
void doSwap(int &a, int &b)
{
int t = a;
a = b;
b = t;
}
};
class SortUp: public AbstractSort
{
/* virtual */int needSwap(int a, int b)
{
return (a > b);
}
};
class SortDown: public AbstractSort
{
/* virtual */int needSwap(int a, int b)
{
return (a < b);
}
};
int main(void)
{
const int NUM = 10;
int array[NUM];
srand((unsigned)time(0));
for (int i = 0; i < NUM; i++)
{
array[i] = rand() % 10+1;
cout << array[i] << ' ';
}
cout << '\n';
AbstractSort *sortObjects[] =
{
new SortUp, new SortDown
};
sortObjects[0]->sort(array, NUM);
for (int u = 0; u < NUM; u++)
cout << array[u] << ' ';
cout << '\n';
sortObjects[1]->sort(array, NUM);
for (int d = 0; d < NUM; d++)
cout << array[d] << ' ';
cout << '\n';
system("pause");
}
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