![]() IUpdateStrategy's, couldn't a Multistrategy hold a Multistrategy, which is holding a Multistrategy (or two) which is hold a Multistrategy, which is holding. Use the same techniques as before: strategies that hold strategies.īut isn't a MultiStrategy an IUpdateStrategy iteself? That is, since a MultiStrategy holds An explicitĬast is required to supress the compile time error ( aop = (AddOp) bop), but may trigger a run-time error if indeed the instance referred to by bop is not of type The above assignment will cause a compile time error because the compiler cannot know if the assignment is possible. Another way of saying this is thatĪ superset contains its subsets but not the other way around. Object of the type of any subclass, but a variable of the type of a particular subclass cannot necessarily reference something of the type of its superclass. That is, a variable of the type of the superclass can always reference an staticly typed as such), which and does not necessarily referenceĪn object of type AddOp. Not as written, because bop is a variable of type IBinaryOp (i.e. Yes! bop is a variable of type IBinaryOp, and aop is defined as referencing an AddOp object, which is an No, because aop is a variable of type AddOp, and MultIOp is not an AddOp, so aop cannot reference an instance of MultOp. Yes, because aop is a variable of type AddOp, and thus can reference an instance of the same type. ![]() If we had MultOp mop = new MultOp(), then mop.getDescription() is perfectly legal. This is because the static typing of bop tells the compiler that it references an IBinaryOp, not the particular concrete type of the object it currently references. No, because bop is a variable of type IBinaryOp, which is not defined as having a getDescription method. It is impossible to tell because it depends on the exact type of the object instance to which myOp refers. The result is 15 because bop now refers to an MultOp instance, whose apply method multiplies its two input values. The result is 8 because bop refers to an AddOp instance, whose apply method adds its two input I am using the same textbook Objects First with Java A Practical Introduction Using BlueJ 6th Edition Barnes Solutions Manual. MultOp is an IBinaryOp, so bop can reference it. ![]() Yes, for the same reasons as the previous exercise! MultOp is an concrete class and can be instantiated. AddOp is an IBinaryOp (technically, AddOp implements the IBinaryOpinterface), so bop can reference it. Yes! AddOp is an concrete class and can be instantiated. IBinaryOp is an interface and does not specify any actual executable code, so it cannot be instantiated. If you do not have it, either consult with someone, or study the problem yourself, or use double and hope for the best.Available under Creative Commons-ShareAlike 4.0 International License. "Choosing the right accuracy in real-world problems requires a good understanding of the nature of machine computing. In fact, most processors are able to work with Float and Double equally effectively, so use the recommendation of Bjorn Stroustrup: Float requires only 4 bytes, but it has only 7 significant digits, while Double is twice as accurate (15 digits), but twice as wasteful. Programmers often cannot select the precision they need for floating-point numbers. Please avoid copyrighted materials.]ĭo not submit any solution of the above exercises at here, if you want to contribute go to the appropriate exercise page. PostgreSQL Exercises, Practice, Solution.R Programming Exercises, Practice, Solution.C# Sharp Programming Exercises, Practice, Solution.If it could, it would not be possible to instantiate an object of that class. b) No, a concrete class can not have abstract methods. That is just the way it is - if it couldn't have concrete methods it would almost be the same as a Java interface. C Programming Exercises, Practice, Solution a) Yes, an abstract class can have concrete methods.Output included with all programs to help you master Java & BlueJ concepts. Twitter Bootstrap Exercises, Practice, Solution Chapterwise solutions to unsolved Java programs of Understanding Computer Applications With BlueJ ICSE Class 10 APC book.CoffeeScript Exercises, Practice, Solution. ![]() jQuery-UI Exercises, Practice, Solution.JavaScript Exercises, Practice, Solution.
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