Java Glossary : Java Cheat Sheet

Java definitions: 0-9 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

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Java Cheat Sheet

This document is a quick summary of the Java language syntax. It is not complete. It just contains the things you may be likely to forget.

I have most of these common patterns built in as SlickEdit macros so I don't have to remember the patterns. I just click a custom icon for the pattern I want. Unfortunately, I thus don't remember them. Without my editor, I would be at a loss to remember where the parentheses and semicolons go.

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" );
      break;
   case 2: System.out.println( "two" );
      break;
   default: System.out.println( "something else" );
   }// end switch (n)

Loops

view

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 e )
         {
         System.out.println( "oops" + e.getMessage() );
         }
      } // end main

   void dangerMethod() throws StrangeException
   {
      if ( unexpected() ) throw new StrangeException ( "oh oh" );
   } // end dangerMethod
   } // end class Test

To help you remember the syntax of catch, think of it as like a method, that gets passed an exception as a parameter.

Try/Catch/Finally

try
   {
   somethingDangerous();
   }
catch ( IOException e )
   {
   System.out.println( "oh oh" );
   throw new BadDataException();
   }
finally
   {
   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 = "abc"
           + "def";
```
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.
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.

Primitive variables include boolean, char, byte, short, int, long, float and double. Strings, arrays and Objects are not considered primitives.

Type	Signed?	Bits	Bytes	Lowest	Highest	Mnemonic
boolean	n/a	1	1	false	true	zero/one
char	unsigned Unicode	16	2	'\u0000' [0] aka Character.MIN_VALUE	'\uffff' [2¹⁶-1] aka Character.MAX_VALUE	Unicode chars are twice as big as C's.
byte	signed	8	1	-128 [-2⁷] aka Byte.MIN_VALUE	+127 [2⁷-1]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
int	signed	32	4	-2,147,483,648 [-2³¹] aka Integer.MIN_VALUE	+2,147,483,647 [2³¹-1] aka Integer.MAX_VALUE	2 gig
long	signed	64	8	-9,223,372,036,854,775,808 [-2⁶³] aka Long.MIN_VALUE	+9,223,372,036,854,775,807 [2⁶³-1] aka Long.MAX_VALUE	9 exabytes, or 9 billion gig
float	signed exponent and mantissa	32	4	±1.40129846432481707e-45	±3.40282346638528860e+38 with 6 to 7 significant digits of accuracy.	rough float
double	signed exponent and mantissa	64	8	±4.94065645841246544e-324	±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

Keywords

Java Keywords
abstract	do	import	public	throws
boolean	double	instanceof	return	transient
break	else	int	short	try
byte	extends	interface	static	void
case	final	long	strictfp	volatile
catch	finally	native	super	while
char	float	new	switch
class	for	package	synchronized
continue	if	private	this
default	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
 */

Java ¤ JavaDoc ¤ keywords ¤ literals ¤ precedence ¤ primitives

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Java Glossary : Java Cheat Sheet

Control Structures

Loops

Try/Catch/Throw

Try/Catch/Finally

Literals

int

byte / short

long

float

double

boolean

String

char

Escape sequences

Primitives vs Immutable Wrapper Objects

Precedence

Keywords

JavaDoc