Java Anatomy

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Data Types

Java has eight primitive which are part of the actual language, and they are not objects.

byte
short
int
long
float
double
char
boolean

Class is also a type.

Comments

Comments are coded with a // or /* */. For example:

// This is a comment

/*  This is a comment over several lines
*/

Literals

The following are escape codes used in Java:

\n New line
\t Tab
\\ backslash
\" Double quotation mark
\' single quotation mark

For example to code

String myString = "Peter said \"Go Home\"";

Operators

Java uses the operators shown below:

+ Addition
- Subtraction
* Multiplication
/ Division
% Moduls

Assignment

Java uses = for assignment, and allows the following:

thisBalance = oldBalance = finalBalance = 4000;

This sets all balances to 4000.

Java uses the following operators

+=
-=
*=
/=

Examples:

thisBalance += oldBalance; is the same as thisBalance = thisBalance + oldBalance;
thisBalance -= oldBalance; is the same as thisBalance = thisBalance - oldBalance;
thisBalance *= interestRate; is the same as thisBalance = thisBalance * interestRate;
thisBalance *= numberPayments; is the same as thisBalance = thisBalance / numberPayments;

i,j,k are commonly used in loops, and we can use the ++ and -- to increment and decrement. For example:

i++; this adds one to i
i--; this subtracts one to i;

If we use an assignment operator, with can do the following;

i=10;
j = i++; // This puts i in j, and then adds one to i, therefore j = 10
j = ++i; // This adds one to i, and then makes the assignment, therefore j =11;

Comparsions

The following operators are possible for comparsions:

== equal
!= not equal
< less than
> greater than
<= less than or equal to
>= greater than or equal to

These operators are used in logical statements.

Logical Operators

&& is AND - only needed expressions are evaluated
|| is OR
& AND - all bracketed expressions are evaluated
| is OR

Let's see this working:

badDebtor = true;
balance = 20000;
goodCustomer = true;

boolean badCustomer = badDebtor | (balance < 10000);
this sets badCustomer to false

If I use

badDebtor = true;
balance = 20000;
goodCustomer = true;

boolean badCustomer = badDebtor || (balance < 10000);

This sets badCustomer to false, but this time Java does not evaluate the second condition. This is because the badDebtor status makes the customer a bad one, regardless of the balance.

Strings

Strings can be added using the + operator:

String customerName = "Joe Harris";
String customerTitle = "Professor";
String customerSalutation = customerTitle + customerName;