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Java question solutions




1. How does Java support the concept of encapsulation?;--------------------------------------------------------------------;2. Describe the difference between an object and a class.;--------------------------------------------------------------------;3. What is the difference between the contents of a Java variable;of a primitive type and a Java variable of a class type?;--------------------------------------------------------------------;4. (a) How is a 'static' class method different from a regular;(non-static) class method?;(b) How is a 'static' variable in a class different from a;regular (instance) variable in a class?;--------------------------------------------------------------------;5. What does the Java keyword 'this' refer to?;--------------------------------------------------------------------;6. What does the Java 'new' operator do?;--------------------------------------------------------------------;7. When does a class require an 'equals' method to be written?;--------------------------------------------------------------------;8. What is method "overriding"? Why would you override a method?;--------------------------------------------------------------------;9. What advantages does inheritance provide in Java?;--------------------------------------------------------------------;10. What is dynamic binding? What advantage does it provide?;--------------------------------------------------------------------;11. How is it possible for two String objects with identical values;not to be equal when compared with the == operator?;--------------------------------------------------------------------;12. Why can a class variable of a base type be set to reference an;object of a derived type, eg;Shape s = new Circle("Blue", 1.0);--------------------------------------------------------------------;13. How can the methods of a derived class access private instance;variables of its base class?;--------------------------------------------------------------------;14. The following try/catch has code to explicitly handle any;IllegalArgumentException thrown. Show the modified code that;will also catch any other type of exception that could be thrown;by code called within the try block.;try;{... methods called here......;catch (IllegalArgumentException e);{... code to handle IllegalArgumentException...;--------------------------------------------------------------------;15. How is the caller's flow of control (sequence of statement;execution) different when an exception is thrown from a method;that it calls, vs. when the method returns normally?;-------------------------------------------------------------------;The following questions are 20 points each. Paste your source code;below each question, and example input and output. Do not include;the code required to test the methods, etc.;--------------------------------------------------------------------;P1. Write a static method that checks if a String represents a valid;integer value and returns true if valid, or false if not. For;example, "123", "-45", and "0" are valid integers, but "x7" and;3.14" are not. Use java.lang.Integer.parseInt() to perform the;actual validity checking inside your method. Your method should;also return false if the parameter String is null or empty.;It should NOT throw any exceptions back to the caller (but may;use exceptions internally).;Use the following prototype for your method;public static boolean isValidInt(String testIntval);Show example output for the following values entered;42";-123";12-34";10.5";x7";" (length 0 string);null (pass a Java null reference in a hardcoded call to isValidInt);--------------------------------------------------------------------;P2. Write a Java method that returns the largest value passed to it.;Use the following prototype;public static int max(int val1, int val2, int val3);// return the largest of the three values...;For example, the following call of your method sets 'n' to 30;int n = max(20, 30, 10);Note that any three values can be passed to this method.;The following would also set 'n' to 30;int n = max(30, 30, 10);Write a main() method to test your max method. It should input;three values, call your max method, and then print the three;values and returned max value as output, eg;Input values: 30 20 10 - max value is 30;The max() method cannot read any input values, nor print any;output values. All input and printing is done by the main();method that calls max().;Paste in both your source code for your max() method, and;the runtime output showing the parameter values and returned;maximum value for the following sample input values;a) 30, 30, 30;b) 10, -10, 20;c) 40, 60, 50;d) 90, 70, 80;e) 50, 50, 25;f) 50, 50, 75;g) 200, 100, 200;h) 200, 400, 200;i) 300, 500, 500;j) 700, 500, 500


Paper#64736 | Written in 18-Jul-2015

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