Short Reference

This is a minimal selection of Java types, classes, methods, operators, keywords and notations. These are things you are most likely to want as a beginner. For full information about them, consult the Java language or library documentation, particularly the library index.

//	Keyword: start of one-line comment
/*	Keyword: start of multi-line comment (ends with */)
=	Keyword: becomes (assignment symbol)
== !=	Is equal to, is not equal to
< <= > >=	Compare
+	Add numbers or join strings
-	Subtract or negate
*	Multiply (must always be explicit)
/	Divide (integer or floating division, depending on types of arguments)
%	Remainder on integer division
&& || !	And, or, not (boolean operators)
()	Notation: bracketing and calling and casting
[]	Notation: used for arrays (declarations and indexing)
{}	Notation: blocks and compound initialisers
BigInteger	Class of unlimited integers (in java.math)
boolean	Type of booleans (see true, false)
char	Type of characters (unicode; 16 bits each)
Character	Class providing operations on chars
class	Keyword: define a new class
double	Type of floating point numbers (double precision)
Double	Class providing operations on floating point numbers
false	Constant (of type boolean)
floor	Round a floating point number down to the integer below with Math.floor(x)
if...	Keyword: testing with if (b) c; or if (b) c; else d;
int	Type of 32-bit integers (up to about 9 or 10 decimal digits)
Integer	Class providing operations on ints
isDigit	Test whether a character is a digit with Character.isDigit(c)
isLetter	Test whether a character is a letter with Character.isLetter(c)
isLowerCase	Test whether a character is a lower case letter with Character.isLowerCase(c)
isUpperCase	Test whether a character is an upper case letter with Character.isUpperCase(c)
isWhitespace	Test whether a character is a space, tab, newline etc with Character.isWhitespace(c)
length	Find the length of an array with a.length or a string with s.length()
Math	Class providing operations on numbers
max	Find the maximum of two ints or doubles with Math.max(x,y)
min	Find the minimum of two ints or doubles with Math.min(x,y)
Object	Class which all other classes extend
parseDouble	Convert a string into a double with Double.parseDouble(s)
parseInt	Convert a string into an int with Integer.parseInt(s)
pow	Math.pow(x,y) takes x to the power y (floating point)
print	Write out a string with System.out.print(s)
println	Write out a string, followed by a newline, with System.out.println(s)
round	Round a floating point number to the nearest integer with Math.round(x)
String	Class of strings (protected, read-only, char arrays)
StringBuffer	Class of manipulable strings (protected char arrays)
substring	Extract a substring from the middle of a string with s.substring(i,j)
System	Class providing standard input, output streams etc
toLower	Convert a character to lower case with Character.toLower(c)
toString	Convert an object into a string with x.toString()
toUpper	Convert a character to upper case with Character.toUpper(c)
true	Constant (of type boolean)

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