CS110- Lecture 3
Feb 7, 2005
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Agenda
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Character Strings
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String Concatenation
Escape Sequence
Variables and Assignment
Primitive Data Types
Program to demonstrate above concepts
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Character Strings
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Java provides the ability to use a string literal,
delimited by double quotation characters.
Examples:
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“Today is Monday”
“100 Morrissey Blvd. “
“”
A string literal can contain any valid
characters , including numeric digits,
punctuation and other special characters.
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Character Strings
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System.out.println(“Welcome to CS110”);
Object dot message (information)
Message from Welcome:
println(“Welcome to CS110”)
Method
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System.out object
Parameter
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Character Strings: String
Concatenation
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A String literal cannot span multiple lines
in a program.
// following statement will give compile
// time error
System.out.println(“Welcome to
CS110:Introduction to Computing”);
String concatenation operator (+) is used
to append one string to the end of
another.
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Character Strings: String
Concatenation
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System.out.println(“Welcome to ” +
“CS110:Introduction to Computing”);
We may chose to send no information to
println method. e.g.
System.out.println();
System.out.println(“Total students :”+ 24);
Number not a String (no
double quotes)
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Character Strings: String
Concatenation
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Strings can be concatenated with numbers.
The number is automatically converted to
String and then the two Strings are
concatenated.
+ operator is also used for arithmetic
addition. Results depends on the types of
data on which it operates.
If both operands are numbers then arithmetic
addition is performed.
If either or both operands are Strings then
String concatenation is performed.
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Character Strings: String
Concatenation
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System.out.println(“No. of students :”+
2 + 4);
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System.out.println(“No. of students :”+
(2 + 4));
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Character Strings: Escape
Sequences
Suppose I want to print “
 System.out.println(“””); //Wrong
 Compiler will be confused
 Java defines several escape
sequences to represent special
characters.
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Character Strings: Escape
Sequences
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An escape sequence begins with the
backslash character (\) which indicates
that the character or characters that
follow should be interpreted in a special
way.
System.out.println(“Welcome to” +
“CS110:\nIntroduction to Computing”);
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Variables
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Variables store values.
You must tell the compiler the kind of value
you want to store, and the name of the place
you will store it
Declaration syntax: type name;
type tells the compiler what kind of value
you want to store
name is the identifier you choose so that you
can refer to the variable elsewhere in the
program.
Declaration may (but need not) initialize
value.
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Variables
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Examples:
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int i = 10;
int i, j;
int i = 10, j = 20;
Naming convention: Method and variable
names start lower case: i, j, main, println.
Internal words capitalized. E.g. noOfStudents
A method’s variables are declared …
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inside the method where they are used
near where they are first used (our convention) or
at the top of the method (another convention).
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Variables
public class Welcome
{
public static void main(String[] args)
{
System.out.println(“CS110:”);
int noOfStudents = 24;
System.out.println(“Total:”+ noOfStudents);
}
When a variable is referenced
}
the value currently stored in it is
used.
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The Assignment Statement
public class Welcome
{
public static void main(String[] args)
{
System.out.println(“CS110:”);
int noOfStudents = 24;
System.out.println(“Total:”+ noOfStudents);
System.out.println(“CS210:”);
noOfStudents = 15; // Assignment statement
System.out.println(“Total:”+ noOfStudents);
}
}
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The Assignment Statement
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A variable can store one value of its
declared type.
A new value overwrites the old value.
Example (primitive types)
noOfStudents
 int noOfStudents = 24;
24
 noOfStudents = 15;
noOfStudents
15
assignment operator
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The Assignment Statement
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x=y
means
assign the value of y to the memory location x
public class AssignmentDemo
{
public static void main(String[] args)
{
int y = 6; // declare y, initialize value
int x = 3; // declare x, initialize value
x = y;
}
}
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The Assignment Operator (=)
int y = 6;
y
6
int x = 3;
x
3
x = y;
y
6
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x
6
x = y is not the same as y = x
This makes mathematicians unhappy
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Constants
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Constants are similar to variables except that
they hold a particular value.
Their value doesn’t change.
You precede a variable declaration with the
reserved word final.
The compiler will produce a error message if
you attempt to change the value.
The only valid place to change their value is
in the initial assignment.
e.g.: final int MAX_CAPACITY = 100;
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Primitive data types
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Every variable must have a data type.
int, float, boolean, ... (Java keywords)
Just eight of them, built into language
Four categories:
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Integers (byte, short, int, long)
Decimals (float, double)
Character (char)
Boolean (boolean)
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Integers
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byte, short, int, long
There are maximum
and minimum
values.
They are signedboth positive and
negative values can
be stored in them.
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Type
Storage Min value Max
(bits)
value
byte 8
-128
short 16
-32768 32767
int
32
long 64
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-231
-263
127
231-1
263-1
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Decimals
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Type
Storag Min value Max
e (bits)
value
float, double
There are maximum
float
32
and minimum
values.
double 64
They are signedboth positive and
negative values can
be stored in them.
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Characters
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char
Storage (16 bits)
They are unsigned.
Character literal is expressed in single
quotes.
E.g.: char c = ‘a’;
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Boolean
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boolean
Just two values true and false
A boolean value cannot be converted to
any other data type, nor can any data
type be converted to a boolean value.
Mostly used in tests
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E.g.: boolean done = false; // we are still not done :)
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Reference types
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String greeting; //What is the data type of greeting?
greeting is of String data type
Welcome welcome ; //What is the data type of welcome?
 welcome is of Welcome data type
Data Types
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Primitive data types
(int, float…)
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Reference data types
(String, Welcome…)
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Reference types
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There are as many classes as you care
to invent. (not limited to 8)
Some of them are predefined in Java
Standard library (String, …..).
int i;
Primitive Data Type
Variable i is of type int
String greeting;
Reference Data Type
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Variable greeting
is an object of
type String
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Reading Exercise
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Section 2.4-2.6
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