Term
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Definition
| Hiding implementation details from users of software to maintain flexibility of possible change in future implementations of software. |
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Term
| How do you implement encapsulation? |
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Definition
| Keep instance variables private, make public accessor & mutator methods, |
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Term
| What is a IS-A relationship? |
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Definition
| it is based on inheritance. eg - horse is type of animal. |
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Term
| What is Has-A relationship? |
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Definition
| A HAS-A B if class A has a reference to an instance fo class B. |
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Term
| How is a HAS-A shown in UML ? |
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Definition
| As a dotted line from the method that calls the method of another class of the same signature. It feels to outsides like the class which has-a has the functionality eventhough it doesnt. |
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Term
| Can constructors be overridden? |
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Definition
| No constructors can only be over loaded |
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Term
| When can you not override a method? |
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Definition
| if it is constructor or a final method? |
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Term
| what must a subclass of abstract class do in order to be concrete? |
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Definition
| the subclass must override all abstract methods. |
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Term
| what happens if a subclass is stored in reference of super class and an overridden method is called on the reference? |
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Definition
| the subclass method gets invoked. |
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Term
| why cant overriding method have more restrictive modifier than a superclass modifier? |
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Definition
| If the subclass has more restrictive modifier then it wont be callable from the super class reference which is not allowed. |
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Term
| what will happen if an overriden method is given a more restrictive modifier than superclass method? |
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Definition
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Term
| what are the rules for overriding a method? |
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Definition
access modifier : cant be more restrictive.
return type: must be same
argument list: must be exactly the same
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Term
| What are the rules for throwing exceptions? |
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Definition
| Overriding method cant throw broader exception though it may throw a narrower exception. |
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Term
| Can you override a private method? |
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Definition
| No if a method is not visible it cant be overriden |
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Term
| How do you invoke a super class version of a method? |
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Definition
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Term
| what are the requirements of an overloaded method? |
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Definition
| Only that it change its return type. |
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Term
| How does a compiler determine what type of methods can be called on an object. |
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Definition
| by looking at the reference type. Only when methods are overridden that compiler will call the method of sub type |
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Term
| can access type of overloaded method change? |
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Definition
| yes it can . be careful if method's acess type is changed it becomes overloaded but not overridden. |
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Term
| When is a class given a default constuctor? |
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Definition
| when there is no constructor written by the programmer. |
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Term
| will a class have a no arg constructor if there is already a constructor which takes arguments? |
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Definition
| no no no . You take on constructore responsibility by defining a constructor. |
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Term
| can constructor be private? |
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Definition
| yes it can. it only means it cant be instantiated from the outside. |
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Term
| are constructor names case sensitive? |
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Definition
| yes constructor name must match exactly the class name |
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Term
| can constructors have return types? |
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Definition
| NO NO NO. this is a good thing. |
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Term
| can you have a method with the same name as constructor |
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Definition
| legal but stupid. If you see a return type then it is a method not a constructor. it will compile. |
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Term
| is there any restriction on this() or super calls in a constructor? |
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Definition
| YES they bust be the first line of code. |
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Term
| what does the constructor insert as the first line of the constructor? |
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Definition
| if there is no this() it inserts a call to super(). so Object.super() will always be invoked. |
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Term
| can yo u call an instance method in a constructor? |
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Definition
| yes but not before super() has run. |
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Term
| can static variables be acessed before a super() call? |
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Definition
| yes. static can but the other one cant |
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Term
| can an abstract class have constructors? |
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Definition
| Yes an abstract class must have constructors and they must get called before the concrete class. |
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Term
| can an interface have a constructor? |
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Definition
| NO - they are not part of an objects inheritance tree. |
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Term
| can a constructor be invoked from within a instance method. |
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Definition
| no it cant be invoked on this. |
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Term
| what is the access modifier of the default constructor? |
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Definition
| it is same at the access modifier of the class. |
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Term
| what happens if the super class doesnt have a no arg constructor? |
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Definition
| in that case you must put in a call to super(args). |
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Term
| what does a call to this() mean? |
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Definition
| it means we are calling a constructor of this class. |
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Term
| if you have a call to this() then does the super() method get called. |
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Definition
| you are only delaying the inevitable sooner or later the super() will get called |
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Term
| can the return type of the overridden method be generalised? |
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Definition
| no it must match the return type of super class method exactly. |
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Term
| can you return null for a method that returns an object? |
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Definition
| Yes you can no matter what type of object you can return null |
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Term
| are there any implicit conversion rules for return types? |
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Definition
| anythign that can be implicitly be converted can be returned. eg. char instread of int |
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Term
| can you return an array where an object is expected. |
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Definition
| yes an array is also an object so new int[] counts. |
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