Transcript CS1101 Group1

CS1101 Group1
Discussion 1
Lek Hsiang Hui
lekhsian @ comp.nus.edu.sg
http://www.comp.nus.edu.sg/~lekhsian/cs1101
Programming background?
Style of discussion
• Discuss previous week lab
• Discuss current week lab
(good to read up the lab question before coming class)
• Go through some concepts of materials
cover during that week
• Quiz
• Mini “in-class” exercises
Other Issues
• Please do NOT call me sir
– I’m also a student! 
• Check your email regularly
• Check out course website regularly
• My cs1101 website (for discussion notes and
related materials)
• Encourage you all to participate actively on the
IVLE forum
• At any point of time, you can ask question,
please let me know whether I’m too soft,
mumbling etc
Questions from lectures?
• Be passionate about programming
• Find sources of practice
– Try out codes in the textbook
– Past yet cs1101/c PE questions
– google for more questions
– http://www.comp.nus.edu.sg/~cs1101x
• Know the concepts
– Look for a src.zip in your jdk folder
System.out.println(“hello world”); is really
System.out.print(“hello world”);
newLine();
• Nature of CS1101
– This module can be very easy or very tough
– Its not one module where you can do last min effort, in fact if you
can follow, its one module where you can feel quite relax just
before exams
• Practice make perfect
• Read before hand later topics
– It’s difficult to relate a certain syntax to how its typically being
used
• Seek help if you are facing problem, don’t wait until
test/exams then you start to panic
Java Programming Style /
Convention
Java Programming Style /Convention
• Please read through
http://www.comp.nus.edu.sg/~cs1101/3_ca
/labs/styleguide/styleguide.html
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Indentation
Comment your code
Classes should start with uppercase
Variables should start with lowercase
Methods should start with lowercase
Final variables/constants should be all uppercase
e.g final int PI = 3.14;
Java Programming Style /Convention
• Variable Names
– Case-sensitive
– Begins with a letter, dollar sign($) or
underscore
– White spaces are not permitted
– Subsequent characters may be a letter, digit,
dollar sign or underscore
CS1101 Labs
CS1101 Labs
• !!! Very important - 20%
• Make sure you indent your code
– If you are using Dr Java, there’s a indentation feature,
just select all your code and press Tab
• Provide comments (in English please!)
• Do early, email me early if you encounter
problems
• Do NOT copy from anyone!
(changing variables names, spacing, shifting
codes around is not going to work!)
Learn how to use the Java API
• http://java.sun.com/javase/6/docs/api/
– Go to google -> Search for java 1.6 api
-> Press I’m feeling Lucky
• E.g
Scanner sc = new Scanner(System.in);
int I = sc.nextInt();
there’s also nextDouble(), nextFloat(), …
Learn how to use the Java API
• Scanner
– Import details : java.util.Scanner
– Constructor
new Scanner(…);
– Methods
return type and method name
int : nextInt();
String : nextLine();
• Math
Numerical Data
int - 32 bit
231 + 1 + (231 - 1) = 232
231 = -2147483648
231 - 1 = -2147483647
Question
Q. What is the result of :
System.out.println(011);
9
How do we get 9?
1 * 81 + 1 * 80 = 9
Octal
(base 8)
Things you should know by now…
Primitive Data Types
•
•
•
•
•
boolean
char
int
float
double
Did you know that char is actually of a
integer type
char a = 'A';
System.out.println(a + 0); //print 65
System.out.println((char)(a + 1)); //print B
Reserved Words
• Reserved words cannot be used as
identifiers (variables names)
Statements
• Statements are code that must do something
• Some typical statements you will see up to now:
• Variable declaration
int num;
• Assignment statements
num = 1;
• Prefix / Postfix statements
++x; x--; etc
• Method calls
Statements
• Java also allow you to define blocks
public static void main(String args[]){
{
int num = 1;
System.out.println(num);
}
int num = 2;
System.out.println(num);
}
prints
1
2
Expressions
• A set of codes that returns a value
E.g
(1 + 1)
this piece of code returns/gives you a
value of 2
• Could be something like
System.out.println( Math.max(1,2) );
Arithmetic Operators
• +,-,*
• / and %
– These 2 operations are usually used when dealing
with getting the digits of a number
• Type promotions
Type Promotions
Type
Able to be promoted to
double
Not able to promote anymore.
float
double
long
float  double
int
long  float  double
char
int  long  float  double
1/2=0!
short
int  long  float  double
byte
short  int  long  float  double
boolean
Not able to promote.
4 / 2.0 = 2.0 not 2
Casting
Compilation
• (<data type>) <expression>
Error!
• Q. What do you think is the output of
public static void main(String args[]){
int a = 10;
int b = (int) a / 2.0;
System.out.println(b);
}
Increment & Decrement Operators
Expression
Operation
x = ++y
Pre-increment
x = y++
Post-increment
x = --y
Pre-decrement
x = y--
Post-decrement
Q.What is the output of
public static void main(String args[]){
int a = 1;
System.out.println(a++);
System.out.println(a);
}
1
2
Increment & Decrement Operators
Expression
Operation
x = ++y
Pre-increment
x = y++
Post-increment
x = --y
Pre-decrement
x = y--
Post-decrement
Q.What is the output of
public static void main(String args[]){
int a = 1;
System.out.println((a++) + (a++));
System.out.println(a);
}
3
3
Increment & Decrement Operators
Q.What is the output of
public static void main(String args[]){
int a = 1;
System.out.println((a++) + (a++));
System.out.println(a);
}
1
A
2
1
3
2
3
3
Boolean Operations
• && , ||, !
• Expressions with
these operators are
evaluated by “shortcircuit evaluation”
• Or lazy evaluation
i.e. expression not evaluation if
we already know the results
• e.g
true || false
(true or anything) -> true, so no
point evaluating the 2nd part
Precedence Order
Order
Operator
1
()
2
!
3
&&
4
||
Boolean Operations
• more e.g
false && true
(false and anything) -> false, so no point evaluating the 2nd
part
Relational Operators
• >,<
• Op= operators
>=, <= , ==, !=
Assignment Operator
•
•
•
•
a= 1 + 3
Step by Step:
a=
(we now need to find a value which will be
given to the LHS)
• a=4
Assignment Operator
• Try out with
int a = 1;
a = (a + (a = (a + 1)));
• a = (1 + (a = (1 + 1)));
• a = (1 + (a = 2)); //assign 2 to a and return value of a
• a = (1 + 2);
• a = 3;
Precedence and Associativity
Operator Type
Operator
Precedence Level
Associativity
Unary
[] . (params) E++ E--
1
Left to right
Unary
unary operators: -E !E ~E
++E --E
2
Right to left
Object creation / Cast
new (type)E
3
Right to left
Arithmetic
*/%
4
Left to right
Arithmetic
+-
5
Left to right
Bitwise
>> << >>>
6
Left to right
Relational
< > <= >=
7
Left to right
Relational
== !=
8
Left to right
Bitwise
&
9
Left to right
Bitwise
^
10
Left to right
Bitwise
|
11
Left to right
Logical
&&
12
Left to right
Logical
||
13
Left to right
Conditional
?:
14
Right to left
Assignment
= += -= *= /= %= >>= <<=
&= ^= |=
15
Right to left