Basic Java Syntax

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Character Set

Other languages, like C or C++, use the ASCII character set. The ASCII character set represents characters by a byte. Actually 7 bits of the byte are used. So at most 128 characters can be represented. This is sufficient to represent the letters of the English alphabet as well as the decimal digits from 0 to 9, and all the punctuation marks. However, if you have to represent letters of the alphabet of other languages, a byte does not offer sufficient storage. Java from the beginning has adopted the 16-bit Unicode system. The ASCII representation is a subset of the Unicode system. To represent a character from another language one has to use the acutal Unicode. The convention used is \uxxxx where xxxx are 4 hexadecimal numbers.

Identifiers

Variables

A variable marks a place in memory to store data. Every variable has a type which tells the compiler how to interpret the string of bits in that memory location. A variable has to be declared before using.

Primitive Types

In Java there are 8 primitive types. The sizes of these types are fixed for the Java Virtual Machine. Octal integer literal begins with 0 and hexadecimal integer literal begins with 0x or 0X.

Declaring a Variable

The generic way of declaring a variable is 
dataType variableName;

int i;
char ch;
boolean found;

Assignment 

variable = expression;

int i = 0;
short x = 0xBF;
float area = length * width;

Constants 


final datatype CONSTANTNAME = VALUE;

final double PI = 3.14159;

final int RATE = 6;
Constants have declared and initialized. You cannot change the value of a constant.

Numeric Operators

A literal is a numeric value that is assigned to a variable like 2 or 5.8. Floating point numbers can be represented in the scientific notation 5.43e+2 which is 543. The numeric operators +, -, *, / can be applied to all integers and floating point numbers. Integer division truncates the result. There are two symbols used to handle overflow:

Shortcut Operators

x += 4 x = x + 4
x -= 4 x = x - 4
x *= 4 x = x * 4
x /= 4 x = x / 4
x %= 4 x = x % 4

Increment and Decrement Operators

Increment and decrement operators can be applied to all integers and floating point types. They can be used either prefix (--x, ++x) or postfix (x--, x++) mode.

Prefix Increment Operation 

int x = 2;
int y = ++x;	// x == 3, y == 3

Postfix Increment Operation 

int x = 2;
int y = x++;	// x == 3, y == 2

Type Conversions

Conversion from a lower range type to higher range type is called widening and is done automatically. However, to go from a higher range type to lower range type (narrowing) you have to explicitly use type casting. 
float x = 5.67;
int i = (int) x;

Character Data Type

Java uses 16-bit Unicode to represent characters. The Unicode representation is of the form '\uxxxx', where xxxx is hexadecimal notation and ranges from 0000 to FFFF. 
char ch = 'A';
char alpha = '\u03b1';

Boolean Data Type

Boolean data types can have two values either true or false.

Comparison Operators

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

Boolean or Logical Operators

NOT !
AND &&
OR ||
EXCLUSIVE OR ^

Truth Table for NOT

A !A
F T
T F

Truth Table for AND

A B A && B
F F F
F T F
T F F
T T T

Truth Table for OR

A B A || B
F F F
F T T
T F T
T T T

Truth Table for EXCLUSIVE OR

A B A ^ B
F F F
F T T
T F T
T T F

Conditional Boolean Operator

If you have an expression of the form A && B then Java evaluates A first. If A is true, then Java evaluates B. If A is false, then Java does not evaluate B.

If you have an expression of the form A || B then Java evaluates A first. If A is true, then Java does not evaluate B. If A is false, then Java does evaluate B.

Bitwise Operators

The bitwise operators include the AND operator &, the OR operator |, the EXCLUSIVE OR operator ^. The bitwise operators applies to boolean and integer types. Both operands are always evaluated.

Shift Operators

Shift operators are applied only to integer types.

Conditional Operator

The conditional operator ? : uses the boolean value of one expression to decide which of the two other expressions should be evaluated. 

exp1 ? exp2 : exp3
If exp1 is true, then exp2 is chosen. If exp1 is false then exp3 is chosen.

Operator Precedence

In Appendix C of your book you have a chart showing the list of operators in Java. When two operators have the same precedence, their associativity determines the order of evaluation. All binary operators are left associative. The assignment operators are right associative.

Operand Evaluation Order

The left hand operand of a binary operator is evaluated before any part of the right hand operand is evaluated. The order for evaluating operands takes precedence over the operator precedence rule.

Expression Statements

An assignment or increment / decrement expression can be made into a statement by adding a semi-colon. An expression statement is executed by evaluating the expression.

if Statement

The if statement allows conditional execution of a statement (with a single if ) or a conditional choice of two statements (with if-else ), executing one or the other but not both. 
if ( Expression )
  Statement;
If the Expression evaluates to true, then Statement is executed. If the Expression evaluates to false then nothing happens. 
if ( Expression )
  Statement1;
else
  Statement2;
If the Expression evaluates to true, then Statement1 is executed. If the Expression evaluates to false then Statement2 is executed.

Switch Statement

The switch statement transfers control to one of several statements depending on the value of an Expression. The type of the Expression must be char, byte, short, or int. 
switch (k)
{
  case 0:  System.out.println ("zero"); break;
  case 1:  System.out.println ("one"); break;
  default: System.out.println ("out of range"); break;
}
The body of a switch statement is known as a switch block. Any statement immediately contained by the switch block may be labeled with one or more case or default labels. When the switch statement is executed, first the Expression is evaluated. If one of the case constants is equal to the value of the expression, then all the statements after the matching case label in the switch block are executed. If no case matches but there is a default label, then all the statements after the matching default label are executed. If there is a break statement then the switch statement completes execution.

while Statement

The while statement executes an Expression and a Statement repeatedly until the value of the Expression is false. The Expression must have type boolean. If the value of the Expression is false the first time it is evaluated, then the Statement is not executed. 
while ( Expression )
  Statement;

do Statement

The do statement executes an Expression and a Statement repeatedly until the value of the Expression is false. The Expression must have type boolean. If the value of the Expression is false the first time it is evaluated, then the Statement is executed at least once. 
do
  Statement
while ( Expression );

for Statement

The for statement executes some initialization code, then executes an Expression, a Statement, and some update code repeatedly until the value of the Expression is flase. 
for ( Init; Expression; Update )
  Statement;
The Init code is a list of statement expressions, the expressions are evaluated in sequence from left to right. If in the Init code, there is a local variable declaration then the scope of the local variable is in the for block. If the value of the Expression is false the first time it is evaluated, then the Statement is not executed.