You want to prevent another developer from redefining specific methods within a child class, or even from subclassing the entire class itself.
Label the particular methods or class as final:
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final public function connect($server, $username, $password) { // Method definition here } |
and:
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final class MySQL { // Class definition here } |
Inheritance is normally a good thing, but it can make sense to restrict it.
The best reason to declare a method final is that a real danger could arise if someone overrides it; for example, data corruption, a race condition, or a potential crash or deadlock from forgetting (or forgetting to release) a lock or a semaphore.
Make a method final by placing the final keyword at the beginning of the method  declaration:
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final public function connect($server, $username, $password) { // Method definition here } |
This prevents someone from subclassing the class and creating a different connect() method.
To prevent subclassing of an entire class, don’t mark each method final. Instead, make a final class:
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final class MySQL { // Class definition here } |
A final class cannot be subclassed. This differs from a class in which every method is final because that class can be extended and provided with additional methods, even if you cannot alter any of the preexisting methods.
