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CS1101 Group1

CS1101 Group1. Discussion 7. Lek Hsiang Hui lekhsian @ comp.nus.edu.sg http://www.comp.nus.edu.sg/~lekhsian/cs1101. Scope of discussion. Mastermind codes CityFlood codes (discussion 5 exercise) Go through Sudoku In class exercise : MyString (lab8) Javadoc. Sudoku.

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CS1101 Group1

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  1. CS1101 Group1 Discussion 7 Lek Hsiang Hui lekhsian @ comp.nus.edu.sg http://www.comp.nus.edu.sg/~lekhsian/cs1101

  2. Scope of discussion • Mastermind codes • CityFlood codes (discussion 5 exercise) • Go through Sudoku • In class exercise : MyString (lab8) • Javadoc

  3. Sudoku • Organization of your program • Don’t just only write codes for solving a problem • Instead, you should format your program in a more modular way.i.e.this method do thisthat method do thatwhen I call, I should get this result, I don’t care how it’s implemented.

  4. Sudoku • It shouldn’t be the case where you call a method and do some extra codes outside to process the result which should be done by the method. E.g. … while(…){ simpleSolver(puzzle); } … //Method to solve the puzzle. static void simpleSolver(int puzzle[][]) { … } Shouldn’t simpleSolver be solving the puzzle?!

  5. General ways to tackle a programming problem (impt!) • Read the question, plan what methods you need. • Write out the method skeletons without the implementation (comment the method if you need) • If you don’t know how to implement a certain method, add in stubs to make sure your program compiles. Think about the implementation later e.g. //this method return a given word //the original word is not modified public String reverse(String word){ return null; //stub }

  6. General ways to tackle a programming problem (impt!) • If a group of codes is always being called at different places, don’t just copy and paste.(Maybe it’s better to create a method for it) • Never hardcode the cases unless you have no choice.(Most probably you will miss out some case)

  7. Javadoc • http://java.sun.com/j2se/javadoc/writingdoccomments/ • Appreciate why you write @author XXX • If you write your program conforming to the javadoc style, you can generate the nice API pages

  8. this keyword • It is a self referencing pointer to this instance. • When is it used? E.g. 1 class Car{ private String color; … public void setColor(String color){ this.color = color; } }

  9. this keyword • It is a self referencing pointer to this instance. • When is it used? E.g. 1 class Car{ private String color; … public void setColor(String color){ this.color = color; } }

  10. this keyword E.g. 2 class Car{ private String color; … public void setColor(String color){ this.color = color; } public void paintBlue(){ this.setColor(“blue”); } }

  11. this keyword • Constructor caserefer to discussion 6

  12. this keyword • It is a self referencing pointer to this *instance*. • When is it not used? E.g. class Car{ private static final String FAV_COLOR; … public static void getFavColor(){ return this.FAV_COLOR; } }

  13. this keyword • It is a self referencing pointer to this *instance*. • When is it not used? E.g. class Car{ private static final String FAV_COLOR; … public static void getFavColor(){ return this.FAV_COLOR; } }

  14. Object is the mother of all classes • As mentioned previously, all user defined classes implicitly extends the java.lang.Object i.e. class A{} A a = new A(); boolean isObject = (a instanceof Object); //true

  15. MyString • In class exercise for this week and the next few weeks • Appreciate OO programming • See yourself as a API developeri.e. write libraries for others to use

  16. \0 MyString • A String is really made up of an array of characters • However the String class by java is not mutable, so you cannot do something like String s = “….”; s.setString(“…”);

  17. MyString • For MyString, we are going to implement a mutable “String” class • What is the special thing about this? • It’s size is variable (so the size can increase) • You are supposed to manually increase it yourself. (do not use ArrayList) • Maybe write a method that create a new char[] that is bigger and transfer all the items there?

  18. MyString • This week you will try to implement the method (in class), will go around the class to see whether you need help: public class MyString{ private char[] charArray; … //this method extend the size of existing charArray //with a larger one, retaining all its previous //value private void ensureCapacity(int minCapacity){ … } }

  19. MyString public class MyString{ … public String toString(){ //? } … }

  20. MyString MyString(java.lang.String str) Constructs a MyString object initialized to the contents of the specified string. • Do you see any way this constructor would need to use one of the MyString method?

  21. MyString public class MyString{ //add in the constructors //and any additional constructors //you think you need }

  22. MyString public class MyString{ //reverse? //charAt? }

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