Hello World Application
class HelloWorldApp {
      public static void main(String[] args) {
            System.out.println("Hello World!");
      }
}



Hello World Applet
import java.applet.*;
import java.awt.*;

public class HelloWorld extends Applet {
      public void paint(Graphics g) {
            // Display "Hello World!"
            g.drawString("Hello world!", 50, 25);
      }
}



Embedding Java Applet





My Applet







Access Specifier

Specifier
class
subclass
package
world



private
X
   
  
  


protected
X
X
X
  


public
X
X
X
X

package
X
  
X
  





Primitve Data Types

Type
Size/Format
Description

(whole numbers)
byte
	 
8-bit two's complement
	 
 Byte-length integer
short
16-bit two's complement
Short integer
int
32-bit two's complement
Integer
long
64-bit two's complement
Long integer

(real numbers)
float
32-bit IEEE 754
Single-precision floating point
double
64-bit IEEE 754
Double-precision floating point
(other types)
char
16-bit Unicode character
A single character
boolean
true or false
A boolean value (true or false)






System Properties

Key
Meaning
"file.separator"
File separator (for example, "/")
 
 
"java.class.path"
Java classpath
"java.class.version"
Java class version number
"java.home"
Java installation directory
"java.vendor"
Java vendor-specific string
"java.vendor.url"
Java vendor URL
"java.version"
Java version number
  
  
"line.separator"
Line separator
  
  
"os.arch"
Operating system architecture
"os.name"
Operating system name
"os.version"
Operating system version
  
  
"path.separator"
Path separator (for example, ":")
  
  
"user.dir"
User's current working directory
"user.home"
User home directory
"user.name"
User account name






Expressions 


	
 postfix operators
[] . (params) expr++ expr--


	
 unary operators
 ++expr --expr +expr -expr ~ !


	
 creation or cast
new (type)expr


	
 multiplicative
* / %


	
 additive
+ -


	
 shift
<< >> >>>


	
 relational
< > <= >= instanceof


	
 equality
== !=


	
 bitwise AND
&


	
 bitwise exclusive OR
^


	
 bitwise inclusive OR
|


	
 logical AND
&&


	
 logical OR
||


	
 conditional
? :


	
 assignment
= += -= *= /= %= &= ^= |= <<= >>= >>>=








Summary of Operator Precedence
The operators in this table are listed in precedence order


	
postfix operators
[] . (params) expr++ expr--


	
unary operators
 ++expr --expr +expr -expr ~ !


	
creation or cast
new (type)expr


	
multiplicative
* / %


	
additive
+ -


	
shift
<< >> >>>


	
relational
< > <= >= instanceof


	
equality
== !=


	
bitwise AND
&


	
bitwise exclusive OR
^


	
bitwise inclusive OR
|


	
logical AND
&&


	
logical OR
||


	
conditional
? :


	
assignment
= += -= *= /= %= &= ^= |= <<= >>= >>>=







Control Flow Statements 

Statement Type
Keyword

	looping    
	while, do-while , for    


	decision making    
	if-else, switch-case    


	exception handling    
	try-catch-finally, throw    


	branching    
	break, continue, label:, return     







 if-else  

A simple if else  
if (boolean expression) {
      statements
} else {
      statements
}


An if statement with multiple expressions and an else statement.  
if (boolean expression) {
      statements
} else if (boolean expression) {
      statements
} else {
      statements
}


An if-else if-else statement  
if (testscore >= 90) {
      grade = 'A';
} else if (testscore >= 80) {
      grade = 'B';
} else if (testscore >= 70) {
      grade = 'C';
} else if (testscore >= 60) {
      grade = 'D';
} else {
      grade = 'F';
}





do - while  

	do {
            statement
	} while (expression);




for  

for (expression) {
      statement
}





switch  
switch (integer expression) {
      case integer expression:
      statements
      break;
      ...
      default:
      statements
      break;
}





try catch - exeptions  
try {
      statements
} catch (exceptiontype name) {
      statements
} catch (exceptiontype name) {
      statements
} finally {
      statements
}