Download Intro to Java

A Look at Java
Categorize Java
• Which paradigm?
• Scripting?
• Declarative or procedural?
• Which generation?
• Low, high, or very high level?
• Compiled or interpreted?
How Programming Works: Pre-Java
1. Programmer types a
program into a text
editor.
•
•
•
This code is called the
source code.
It is saved as a file on your
computer, much like any
other file you create.
Since the code is humanreadable, it is usually kept
private.
#include <iostream.h>
main()
{
cout << "Hello World!";
return 0;
}
How Programming Works: Pre-Java
1. Source Code
2. A program called a
compiler reads the code
and makes machine code
instructions specific to the
type of machine you are
running on.
•
•
This code is NOT humanreadable.
This is what comes on
software CDs, so that the
code remains proprietary.
#include <iostream.h>
main()
{
cout << "Hello World!";
return 0;
}
Compiler
_main _TEXT SEGMENT
_argc$ = 8
_argv$ = 12
_main PROC
NEAR ; COMDAT
00000 68 00 00 00 00 push OFFSET
FLAT:??_C@_0M@KPLPPDAC@Hello?5World?$AA@
00005 e8 00 00 00 00 call _printf
0000a 83 c4 04 add esp, 4
0000d 33 c0 xor eax, eax
How Programming Works: Pre-Java
1. Source Code
2. Compiled to Machine Code
3. Run on the computer
- Now the program can be run, but
only on the machine it was
compiled for.
Hello
World!
Executed by a
machine with
Intel 32-bit
processor
#include <iostream.h>
main()
{
cout << "Hello World!";
return 0;
}
Compiler
_main _TEXT SEGMENT
_argc$ = 8
_argv$ = 12
_main PROC
NEAR ; COMDAT
00000 68 00 00 00 00 push OFFSET
FLAT:??_C@_0M@KPLPPDAC@Hello?5World?$AA@
00005 e8 00 00 00 00 call _printf
0000a 83 c4 04 add esp, 4
0000d 33 c0 xor eax, eax
Java Programming Language
• James Gosling, Sun Microsystems, 1991
• Idea: Want a computer application to
control the appliances in a home
• But - different chips on each
• Need: Programming language that works
on any machine
• 3 years later, Internet hits, and we realize
portability is a great idea…
How Java Programming Works
1. Programmer types a
program into a text
editor.
•
•
•
This code is called the
source code.
It is saved as a file on your
computer, much like any
other file you create.
Since the code is humanreadable, it is usually kept
private.
public class Hello{
public static void main(
String[] args){
System.out.println(
“Hello World!”);
}
}
How Java Programming Works
1. Source Code
2. The Java compiler reads
the code and makes an
intermediate code called
bytecode.
•
•
Again, this code is NOT
human-readable.
Again, this is what comes on
software CDs, so that the
code remains proprietary.
public class Hello{
public static void main(
String[] args){
System.out.println(
“Hello World!”);
}
}
Java Compiler:
Same for all
machines
0: iconst_2
1: istore_1
2: iload_1
3: sipush 1000
6: if_icmpge
44
9: iconst_2
10: istore_2
11: iload_2
12: iload_1
13: if_icmpge
31
How Java Programming Works
1. Source Code
2. Compiled to Bytecode
3. Interpreted by JVM (Java
Virtual Machine) This
program reads bytecode
and translates it directly to
whatever machine code is
needed.
_main _TEXT SEGMENT
_argc$ = 8
_argv$ = 12
_main PROC
NEAR ; COMDAT
00000 68 00 00 00 00 push OFFSET
FLAT:??_C@_0M@KPLPPDAC@Hello?5World?$AA@
00005 e8 00 00 00 00 call _printf
0000a 83 c4 04 add esp, 4
0000d 33 c0 xor eax, eax
Interpreted
by JVM
public class Hello{
public static void main(
String[] args){
System.out.println(
“Hello World!”);
}
}
Java Compiler:
Same for all
machines
0: iconst_2
1: istore_1
2: iload_1
3: sipush 1000
6: if_icmpge
44
9: iconst_2
10: istore_2
11: iload_2
12: iload_1
13: if_icmpge
31
How Java Programming Works
1. Source Code
2. Compiled to Bytecode
3. Interpreted by JVM to
4.
Machine Code
Executed by machine
Java Compiler:
Same for all
machines
Hello
World!
_main _TEXT SEGMENT
_argc$ = 8
_argv$ = 12
_main PROC
NEAR ; COMDAT
00000 68 00 00 00 00 push OFFSET
FLAT:??_C@_0M@KPLPPDAC@Hello?5World?$AA@
00005 e8 00 00 00 00 call _printf
0000a 83 c4 04 add esp, 4
0000d 33 c0 xor eax, eax
public class Hello{
public static void main(
String[] args){
System.out.println(
“Hello World!”);
}
}
Interpreted
by JVM
0: iconst_2
1: istore_1
2: iload_1
3: sipush 1000
6: if_icmpge
44
9: iconst_2
10: istore_2
11: iload_2
12: iload_1
13: if_icmpge
31
Java Overview
Source Code: MUST
be named Hello.java
public class Hello{
public static void main(String[] args){
System.out.println(“Hello World!”);
}
}
Bytecode: will be
saved as Hello.class
0: iconst_2
1: istore_1
2: iload_1
3: sipush 1000
_main _TEXT SEGMENT
_argc$ = 8
_argv$ = 12
_main PROC
NEAR ; COMDAT
0000 68 00 00 00 00 push
00005 e8 00 00 00 00 call
0000a 83 c4 04 add esp,
0000d 33 c0 xor eax,
Mac
Windows
FLAT:??_C@_0M@
KPLPPDAC@Hello?5
World?$AA@
00005 e8 00 00 00 00
0000a 83
Hello
World!
Unix
Whatever
So, what about Eclipse?
• What is eclipse?
• How does it work?
• What languages will it work for?