Cheat Sheet

Java All-in-One For Dummies

Writing Java statements (like for and if) and classes (like Math and NumberFormat) help you start and build strong programs. Variables hold different kinds of Java data types: numbers, characters, and true/false numbers. You designate Java operations that can be performed on operands, including arithmetic operators, relational operators (or binary) and logical operators (or Boolean).

Common Java Statements

Java statements build programs. Every Java class must have a body, which is made up of one or more statements. You can write different kinds of statements, including declaration and expression.

The break statement

break;

The continue statement

continue;

The do statement

do
    {statements...}
while (expression);

The for statement

for (init; test; count)
    {statements...}

The enhanced for statement

for (type variable : array-or-
collection) {statements...}

The if statement

if (expression)
    {statements...}
else
    {statements...}

The throw statement

throw (exception)

The switch statement

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

The while statement

while (expression)
    {statements...}

The try statement

try
    {statements...}
catch (exception-class e)
    {statements...}...
finally
    {statements...}
try
    {statements...}
finally
    {statements...}

Primitive Data Types

Java data types are the kind of data you can store in a variable. Primitive data types are defined by the language itself. Java defines a total of eight primitive types. Of the eight primitive data types, six are for numbers, one is for characters, and one is for true/false values. Of the six number types, four are types of integers, and two are types of floating-point numbers.

Type Wrapper Class Parse Method of Wrapper Class
int Integer int parseInt(String s)
short Short short parseShort(String s)
long Long long parseLong(String s)
byte Byte byte parseByte(String s)
float Float float parseFloat(String s)
double Double double parseDouble(String s)
char Character (none)
boolean Boolean boolean parseBoolean(String s)

Math and NumberFormat Classes

Java classes lay the foundation for your programs. The Java Math and NumberFormat classes let you program number values, as well as format numbers and currencies.

The Math Class
Method Description
num abs(num y); Absolute value of y (num can be any numeric data type)
num max(num y, num z); Maximum of y and z
num min(num y, num z); Minimum of y and z
double = Math. random(); Random number, such that 0.0 < x <= 1.0
The NumberFormat Class
Method Description
NumberFormat getNumberInstance(); Gets an instance that formats numbers.
NumberFormat Gets an instance that formats currency.
String format(x); Formats the specified number.

Java Operators

An operator designates a mathematical operation or some other type of operation that can be performed on operands. Java has arithmetic operators, relational operators (also known as binary operators) and logical operators (also known as Boolean operators).

Arithmetic
Operator Description
+ Addition
- Subtraction
* Multiplication
/ Division
% Remainder
++ Increment
Decrement
+= Addition and assignment
-= Subtraction and assignment
*= Multiplication and assignment
/= Division and assignment
%= Remainder and assignment
Relational
Operator Description
== Equal
!= Not equal
< Less than
<= Less than or equal to
> Greater than
>= Greater than or equal to
Logical
Operator Description
! Not
& And
&& Conditional and
| Or
|| Conditional or
^ xor
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