Transcript 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
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Mastermind codes
CityFlood codes (discussion 5 exercise)
Go through Sudoku
In class exercise : MyString (lab8)
– Javadoc
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 this
that method do that
when I call, I should get this result, I don’t care
how it’s implemented.
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?!
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
}
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)
Javadoc
• http://java.sun.com/j2se/javadoc/writingdo
ccomments/
– Appreciate why you write @author XXX
• If you write your program conforming to
the javadoc style, you can generate the
nice API pages
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;
}
}
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;
}
}
this keyword
E.g. 2
class Car{
private String color;
…
public void setColor(String color){
this.color = color;
}
public void paintBlue(){
this.setColor(“blue”);
}
}
this keyword
• Constructor case
refer to discussion 6
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;
}
}
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;
}
}
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
MyString
• In class exercise for this week and the
next few weeks
• Appreciate OO programming
• See yourself as a API developer
i.e. write libraries for others to use
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(“…”);
\0
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?
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){
…
}
}
MyString
public class MyString{
…
public String toString(){
//?
}
…
}
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?
MyString
public class MyString{
//add in the constructors
//and any additional constructors
//you think you need
}
MyString
public class MyString{
//reverse?
//charAt?
}