Java Cheat Sheet
found at http://mindprod.com/jgloss/jcheat.html
Control Structures
// I F / E L S E
if (
a > b )
{
System.out.println ( a );
}
else
{
System.out.println ( b );
}
// I F / E L S E : is x in range low .. high?
if (
low <= x && x <= high )
{
System.out.println (
}
"in range"
);
else
{
System.out.println (
}
"out of range"
);
// S W I T C H / C A S E
switch (
n )
{
case 1:
System.out.println (
"one"
);
"two"
);
break;
case 2:
System.out.println (
break;
default:
System.out.println (
"something else"
);
}// end switch (n)
Loops
// F O R
// Note lack of ; after i++
for ( int i=0
; i<n ; i++ )
{
System.out.println( i );
}
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Course Syllabus
// R E V E R S E
for ( int i=n-1
F O R
; i>=0 ; i-- )
{
System.out.println( i );
}
// D U A L
F O R
// Note lack of ; after j++
for ( int i = 0
,j = 0; i<n ; i++ ,j ++ )
{
System.out.println( i );
}
// However, this is illegal!
for ( int i=0
,
float r
=1.0; i <n; i ++ ,r= r *2.0 )
{
System.out.println( i );
}
// E N U M E R A T I O N
// Note ; after hasMoreElements().
for (
Enumeration
e
= props.propertyNames (); e.hasMoreElements(); )
{
String key = (String) e.nextElement();
System.out.println ( key );
}
// I T E R A T O R
// Note ; after hasNext()
for (
Iterator
iter
= list.iterator (); iter.hasNext(); )
{
String key = (String) iter.next();
System.out.println( key );
}
// I T E R A T O R : alternate
Iterator
someFiles
= getFilesToProcess();
while (
someFiles.hasNext ())
{
File
...
}
= (File) someFiles.next ();
f
// W H I L E
while (
moreData () )
{
readIt();
}
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Course Syllabus
// D O / W H I L E
do
{
readIt();
if (
if (
done () )
break;
bypassThisOne () )
processIt();
}
while (
continue;
moreData () );
The variables used in the while (boolean) clause can't be declared inside the while loop. The inside
of the loop is considered a separate inner block.
Try/Catch/Throw
public class Test extends StandardTest
{
public static void main
(String []
args)
{
try
{
dangerMethod();
}
catch (
StrangeException
{
System.out.println (
}
e
)
"oops"
+ e.getMessage () );
} // end main
void dangerMethod() throws StrangeException
{
if (
unexpected () ) throw
} // end dangerMethod
new StrangeException
(
"oh oh"
) ;
} // end class Test
To help you remember the syntax of
exception as a parameter.
catch, think of it as like a method, that gets passed an
Try/Catch/Finally
try
{
somethingDangerous();
}
catch (
IOException
{
System.out.println(
e
)
"oh oh"
throw new BadDataException
) ;
();
}
finally
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{
file.close(); // always executed
}
Literals
A literal is an explicit number or string constant used in Java programs. Here is a list of all the variant
forms I have found Java to support:

int
1, -1, hex ints 0x0f28, unicode hex '\u003f', octal 027, Integer.MAX_VALUE (2,147,483,647),
Integer.MIN_VALUE (-2,147,483,648)
Beware! A lead 0 on an integer implies OCTAL. That was a major design blunder inherited from
C, guaranteed to introduce puzzling bugs. Be especially careful when specifying months or
days, where you naturally tend to provide a lead 0.

byte / short
There is no such thing as a byte or short literal. You would have to write it with a cast e.g.
(byte)0xff or (short)-99.

long
3L, -99l, 0xf011223344L (Beware! some compilers will just chop the high bits from literals
without the trailing L even when assigning to a long.), Long.MAX_VALUE
(9,223,372,036,854,775,807), Long.MIN_VALUE (-9,223,372,036,854,775,808).

float
1.0345F, 1.04E-12f, .0345f, 1.04e-13f, Float.NaN.

double
5.6E-120D, 123.4d, 0.1, Double.NaN, Math.PI.
Note floating point literals without the explicit trailing f, F, d or D are considered double. In
theory you don't need a lead 0, e.g. 0.1d may be written .1d, though the Solaris and Symantec
compilers seem to require it.

boolean
true and false.

String
"ABC", enclosed in double quotes. You may not split strings over two lines. If you must, code
like this:
String s =
+ "def";
"abc"
There is no speed penalty for the + concatenation. It is done at compile time. String literals
can be used anywhere you might use a String reference. e.g. "abc".charAt(1) is legal. For
problematic characters like embedded ", see escape sequences below.
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
char
'A', enclosed in single quotes, or integer forms e.g. (char)45, (char)0x45,
'\u003f'. For problematic characters like embedded ', see escape sequences below.

Escape sequences
inside char and string literals include:
'\u003f' unicode hex, (must be exactly 4 digits)
'\n' newline, ctrl-J (10, x0A)
'\b' backspace, ctrl-H (8, 0x08)
'\f' formfeed, ctrl-L (12, 0x0C)
'\r' carriage return, ctrl-M (13, 0x0D)
'\t' tab, ctrl-I (9, 0x09)
'\\' backslash,
'\'' single quote (optional inside " "),
'\"' double quote (optional inside ' '),
'\377' octal (must be exactly 3 digits. You can get away with fewer, but then you create
an ambiguity if the character following the literal just happens to be in the range 0..7.)
\007 bel, ctrl-G (7, 0x07)
\010 backspace, ctrl-H (8, 0x08)
\013 vt vertical tab, ctrl-K (11, 0x0B)
\032 sub, eof, ctrl-Z (26, 0x1A)

Unsupported
There is no Pascalian '#nnn' style way of specifying decimal constants. Just use char c =
123;
The following C forms are not supported: '\a' alert
'\v' vertical tab
'\?' question mark
'\xf2' hex. Use the unicode \uffff form for printable characters.
Primitives
Primitive variables include boolean, char, byte, short, int, long, float and double. Strings,
arrays and Objects are not considered primitives.
Type
boolean
char
Signed
?
Bit
s
Byte
s
n/a
1
1
false
true
zero/one
2
'\u0000' [0] aka
Character.MIN_VALUE
'\uffff' [216-1] aka
Character.MAX_VALUE
Unicode
chars are
twice as big
as C's.
unsigne
d
Unicode
16
Lowest
Highest
Mnemonic
byte
signed
8
1
-128 [-2 ] aka
Byte.MIN_VALUE
+127 [2 -1]aka
Byte.MAX_VALUE
Bytes are
signed, so
half the
usual 255
range.
short
signed
16
2
-32,768 [-215] aka
Short.MIN_VALUE
+32,767 [215-1] aka
Short.MAX_VALUE
32K
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Course Syllabus
int
signed
long
signed
float
signed
expone
nt and
mantiss
a
double
signed
expone
nt and
mantiss
a
32
64
32
64
4
-2,147,483,648 [-231] aka
Integer.MIN_VALUE
+2,147,483,647 [231-1]
aka Integer.MAX_VALUE
2 gig
8
9,223,372,036,854,775,80
8 [-263] aka
Long.MIN_VALUE
+9,223,372,036,854,775,
807 [263-1] aka
Long.MAX_VALUE
9 exabytes,
or 9 billion
gig
4
±1.40129846432481707e45
±3.40282346638528860e+
38
with 6 to 7 significant
digits of accuracy.
rough float
8
±4.94065645841246544e324
±1.79769313486231570e+
308
with 14 to 15 significant
digits of accuracy.
high
precision
float
Primitives vs Immutable Wrapper Objects
Contrast that table of primitives, with this table of basic Java types:
Mutable Primitives
Immutable Objects
boolean
Boolean
ordinary signed byte Byte
unsigned byte
Byte
short
Short
char
Character
int
Integer
long
Long
float
Float
double
Double
char[]
String
Precedence
Operator Precedence
Precedence
Operator
Association
Notes
1
(prefix) ++
-(unary) + ~!
(cast)
++ prefix means preincrement, . ~ is bitwise not for ints. ! is
logical not for booleans. Nearly always, you have to put the
Right (prefix)
expression after ! in parentheses. You might as well make a
habit of always doing it.
1
(postfix)
++ --
Right
(postfix)
++ postfix means postincrement
2
*/%
Left (infix)
% is modulus, remainder. / is integer division for ints and
floating point division for doubles.
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3
+-
Left (infix)
a - b - c means (a - b) - c not a - ( b - c ),
additive operations are performed left to right. + also
means concatenation.
There is no <<< operator because it would be identical to
<<. You have to keep your wits about you when doing
unsigned shifts to remember all right shifts must be done
with >>>.
4
<< >> >>>
Left (infix)
5
< > <= >=
instanceof
Left (infix)
6
== !=
Left (infix)
Pascal's <> not equal will not work. == and != work on
booleans too, often saving a forest of if/elses.
7
&
Left (infix)
Bitwise AND mostly for for ints.
XOR for ints. It is the difference operator. It is true if the
boolean operands are different. e.g.
false ^ false == false
false ^ true == true
true ^ false == true
true ^ true == false
8
^
Left (infix)
It is useful in cryptography because of this magic property of
encryption and decryption with a random scrambler
number.
long encrypted = message ^ scrambler ;
long decryped = encrypted ^ scrambler ;
If you XOR twice with the scrambler, you get right back
where you started. For booleans it is clearer to use a != b
instead of a ^ b and a == b instead of !( a ^ b)
9
|
Left (infix)
bitwise OR mostly for ints.
10
&&
Left (infix)
short circuit logical AND for booleans.
11
||
Left (infix)
short circuit logical OR for booleans.
12
?:
Right (
ternary )
a = b ? c : d; is shorthand for if ( b ) a = c;
else a = d;
13
= *= /= +=
-=
<<= >>=
>>>=
&= ^= |=
Right (infix)
These make proofreading easier by eliminating typing a
variable name twice.
Keywords
Java Keywords
abstract do
import
boolean
double
instanceof return
transient
break
else
int
short
try
byte
extends
interface
static
void
case
final
long
strictfp
volatile
POS 407 -- Computer Programming II
public
throws
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Course Syllabus
catch
finally
native
super
char
float
new
switch
class
for
package
synchronized
private
this
continue if
default
while
implements protected throw
Reserved keywords (not currently in use)
const
goto
Reserved Literals
null
true
false
JavaDoc
/** FormattedTextField.java
* @author Roedy Green
* @version 1.34 1998 January 18
* @deprecated Noreplacement
* @deprecated Replaced by otherMethod(int)
* @see otherMethod
* @see #otherMethod
* @see java.awt.Component#repaint
* @see <a href="http://mindprod.com/gloss.html">Java & Internet Glossary</a>
* @see "design patterns by Gamma et. al"
* @param x <b>pixels</b> right of the origin.
* @return number of oranges.
* @exception java.beans.PropertyVetoException when mask is invalid
* @since JDK1.1
*/
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Course Syllabus