Java Syntax Part I

•Comments

•Identifiers

•Primitive Data Types

•Assignment

Java Syntax - Comments

• Type 1: – begins with /*– continues till the next */

• Type 2:– begins with //– continues till the end of the line

• Type 3:– begins with /**, and continues till the next */

Java Syntax -- comments (style)

• Good programming practice– Put helpful comments

• at the beginning of a big block

• on the same line of certain statements

– Good internal documentation is very important

Java Syntax -- comments (example)

//---------------------------------------------------------------------------

// withdraw: withdraw money from banking_account

// Input : amount = the amount of money to withdraw

//----------------------------------------------------------------------------

void withdraw(float amount)

{

//----------- if not enough money in the account ----

…

//----------- else, we have enough money in the account ----

...

}

Java Syntax -- Identifiers

• Names of declared entities– variables, constans, labels…

• Must start with a letter: [A..Z][a..z]– including _ (underscore) or $ (dollar sign)

• Followed by letters or digits

• Java language keywords can not be used as identifiers.

Java Syntax -- Identifiers (example)

accountNumber

length1

length_2

Java Syntax -- Primitive Data Types

• boolean: takes only 2 values true or false• Example: boolean done = false;

• char : contains a character• Example: char ch;

• byte, short, int and long : Integral Types• Example: int num = 3;

• float, double : Floating-Point Types• Example: float temperature = 37.6;

Java Syntax -- Assignment

• Example using integers: int i = 2; // create an integer variable

i = 5; // change i to 5

int j = 6; // create an integer variable j

i = j*3 // multifply the value of j by 3

// now i = 18

i = i + 4; // NOT AN EQUATION!

// i was 18, i+4=22; new i=22.

• Calculate the value on the RIGHT HAND SIDE

• Assign the result to the variable on the LEFT HAND SIDE

Java Syntax -- Assignment (Abbreviations)

• Examples:

j = j + 1; // as before

j += 1; // same as j = j + 1;

j += 5; // same as j = j + 5;

j++; // same as j = j + 1;