Java中的Abstract和Interface的区别

问题

I will give you an example first:

public interface LoginAuth{
public String encryptPassword(String pass);
public void checkDBforUser();
}

Now suppose you have 3 databases in your application. Then each and every implementation for that database needs to define the above 2 methods:

public class DBMySQL implements LoginAuth{
// Needs to implement both methods
}
public class DBOracle implements LoginAuth{
// Needs to implement both methods
}
public class DBAbc implements LoginAuth{
// Needs to implement both methods
}

But what if encryptPassword() is not database dependent, and it’s the same for each class? Then the above would not be a good approach.

Instead, consider this approach:

public abstract class LoginAuth{

public String encryptPassword(String pass){

// Implement the same default behavior here

// that is shared by all subclasses.

}

// Each subclass needs to provide their own implementation of this only:

public abstract void checkDBforUser();

}

Now in each child class, we only need to implement one method - the method that is database dependent.

I tried my best and Hope this will clear your doubts.

这个问题的就是怎么是使用interface和abstract更好，举了一个例子，如果我们定义一个规范然后不同的实现不同，那么就是interface比较好，如果有一部分公共，给予集成或者实现的类更多选择余地，那么使用abstract比较好。而且接口中只要定义了方法，集成的类就必须完全实现，但是abstract没有这个限制。