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>Packages & Classes

v Data types, Operators, Keywords, Definition, Flow control, Functions, Comments

Program development

Download: Sun Java Development Kit (JDK)
Java Decompiler: Jad

Data types

Operators
v unary, binary, assignment, boolean, bit-logical

unary

+	+op	promotion of byte, short, char to int
-	-op	negation

binary

+
-
*
/	op1 / op2
&	op1 % op2    //modulus

assignment

++ 	op++         //op = op + 1
-- 	op--         //op = op - 1
+= 	op1 += op2   //op1 = op1 + op2
-=
*=
/=
%=
&=
|=
^=
<<=
>>=
>>>=

boolean

relational

>
>=
<
<=
==
!=
instanceof		op1 instanceof op2		//true, if op1 and op2 are assignment compatible

 

conditional

&&	op1 && op2   //and - conditionally evaluates op2
||	op1 || op2   // or - conditionally evaluates op2
!	!op          //not
&	op1 & op2    //and - always evaluates op2
|	op1 | op2    // or - always evaluates op2
?	expression ? op1 : op2

 

bitwise, logical

<<   op1 << op2  //shift op1 left op2 bits
>>   op1 >> op2  //shift op1 right op2 bits unsigned
>>>  op1 >>> op2 //shift op1 right op2 bits signed
&    op1 & op2   //bitwise and
|    op1 | op2   //bitwise or
^    op1 ^ op2   //bitwise xor
~    ~ op        //bitwise complement

Keywords (reserved)
abstract, boolean, break, byte, case, catch, char, class, const, double, else, extends, final, finally, float, for, goto, if, int, interface, long, native, new, null, package, private, protected, static, super, switch, synchronized, this, throw, throws, transient, try

abstract

boolean

byte

char

const

default

double

final

// constant variable
final int pi = 3.1416;

// may be set later - once
final int max;
---
max = 100;

float

goto

implements
instanceof
int

int count = 0;

interface
long
native
new

int[] arrayOfInts; //no space allocated

// allocate space for 10 ints:
int[] arrayOfInts = new int[10];

string[] arrayOfStrings = new String[10];
// space for 10 string-pointers is now allocated
// but no space for the strings!
// so, allocate some space for the strings:
for( int i=0; i<arrayOfStrings.length; i++)
  arrayOfStrings[i] = new String("String #" + i);

null

package
private
protected
short
super
synchronized
this
throws

public static void countChars( Reader in) throws IOException

transient

volatile

definition : class, extends, import, public, static, void,

class

ex:
class HelloWorldApp
//this class is placed in the default package
{ //variables and methods
  public static void main(String[] args)
  { . . .
  )
}

extends

indicates a subclass of a class
ex:
import java.applet.Applet;
public class HelloWorld extends Applet
ex:
public class HelloWorld extends java.applet.Applet

import

By importing classes or packages (groups of classes), a class can refer to other classes.
NB: the lang package is automatically imported.
class import Ex:
import java.applet.Applet;
import java.awt.Graphics;
package import Ex:
import java.applet.*;
import java.io.*;

public

public : allows any class to call this method
ex:
public static void main()
public class count()

static

static : a class method
ex:
public static void main()

void

void : the method returns no value
ex:
public static void main()

 

flow control, loops : do...while, for, if...else, switch...case, while

break

continue

do ... while

do
{ statements
} while( condition);

for

for( initialization; termination; increment)
  statement;
for( int i=0; i<10; i++) ...

if ... else

if( expression) statement;
else statement;

try ... catch ... finally

return

switch ... case

switch( variable)
{ case val1: statement1; break;
  case val2: statement2; break;
  ---
  default: statement;
}

throw

while

ex:
int count = 0;
while( in.read() != -1)
count++;

Functions

Ex:
public static void main( String[] args) throws IOException
{ if ( args.length >= 1)
    countChars( new FileReader( args[0]));
  else
    System.err.println("Usage: Count filename");
}

Comments

// text
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/* text */
text is ignored by the compiler javac
/** documentation */
documentation is ignored by the compiler javac
but used by javadoc for automatically generated documentation