An introduction to Java

An introduction to Java
Bruce Eckel, Thinking in Java, 4th edition,
PrenticeHall, New Jersey, cf.
http://mindview.net/Books/TIJ4
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José Valente de Oliveira
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http://oreilly.com/pub/a/oreilly/news/languageposter_0504.html
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1
A short history of OO languages
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A (tiny) family of programming languages
Fortran
Cobol
BASIC Algol 60
Simula
C
C++
Algol 68
Pascal
Perl Modula 3
LISP
PL/1
ML
Scheme
Smalltalk
Dylan
Ada
Prolog
Java
C#
Python
Ruby
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The 70s at XEROX Palo Alto Research Center
„
„
„
„
„
Graphical User Interface
Ethernet
First personal computer
PostScript Printers
Object-Oriented Programming
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Dynabook, 1972
3-6
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“Don’t worry about what anybody else is going to do…
The best way to predict the future is to invent it.
Really smart people with reasonable funding can do just
about anything that doesn't violate too many of
Newton's Laws!”
(Alan Kay, 1971)
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Smalltalk
„
„
„
„
Everything is an object
Objects communicate by sending and
receiving messages
Objects build up from other objects
How do you do
b
aa ++ b
send the object a the message + b
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4
Smalltalk – A typical method
Point >> dist: aPoint
“Answer the distance between the receiver
and aPoint.”
| dx dy |
dx := self x – aPoint x.
dy := self y – aPoint y.
^(dx*dx + (dy*dy)) sqrt
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Mainstream object-oriented programming languages
‰
‰
Smalltalk (Alan Kay, Xerox PARC, 1971)
C++ (Bjarne Stroustrup, Bell Labs, 1983)
B. Stroustrup
‰
‰
‰
Java (James Gosling, Sun Microsystems, 1995)
Objective C (Brad Cox, and Tom Love,1980s)
C# (Microsoft, 2000)
J. Gosling
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Long term trends of Tiobe indices as of September 2015
From:
http://www.tiobe.com
Java main features
„
Sun said that Java is characterized by the following features:
‰ Simple
‰
Architecture neutral
‰
Object-oriented
‰
Portable
‰
Distributed
‰
Robust
‰
Secure
‰
Efficient
‰
Multithreaded
‰
Dynamic
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6
Executing Java code
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Write Once Run Anywhere
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7
Overview of the Java platform
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Java platform diagram
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8
Java – from the very beginning
// file: First.java
public class First {
public static void main(String[] args) {
System.out.print(“Hello Java");
}
}
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Control strucutures
„
All control structures available in C/C++ are
also available in Java
„
The same goes to relational and logic
operators
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Primitive data types
Data
type
byte
Range of values
-128 .. 127 (8 bits)
short
-32,768 .. 32,767 (16 bits)
int
-2,147,483,648 .. 2,147,483,647 (32 bits)
long
-9,223,372,036,854,775,808 .. ... (64 bits)
float
+/-10-38 to +/-10+38 and 0, about 6 digits precision
double
+/-10-308 to +/-10+308 and 0, about 15 digits precision
char
Unicode characters (generally 16 bits per char)
boolean true or false (1 bit)
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public class Average {
public static void main (String [] args) {
int n;
Scanner sc = new Scanner(System.in);
At this point I can code in Java just
do{
like");I used to code in C. I can even
System.out.print("N:
n = sc.nextInt(); use functions. I’m not using the power
of oop though
if (n<=0) System.out.println(“Invalid!");
} while(n<=0);
float [] x = readFloatArray(sc, n);
// computing the average
float sum=0.0f;
for(int i=0; i<n; i++ )
sum +=x[i];
float av = sum / n;
System.out.println(“Average: " + av );
}
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private static float [] readFloatArray(Scanner sc, int n) {
float [] fa = new float [n];
for(int i=0; i< fa.length; i++ ) {
System.out.print("x"+i+"? ");
fa[i] = sc.nextFloat();
}
return fa;
}
}
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3-21
To take away today
„
Java:
‰ A little bit of History
‰ Goals and characteristics
‰ First programs
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3-22
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