system development with java lecture 2. rina zviel-girshin @asc2 errors a program can have three...

System development with Java

Lecture 2

Rina Zviel-Girshin @ASC 2

Errors

• A program can have three types of errors:• Syntax and semantic errors – called compile-

time errors• Run-time errors – occur during program

execution• Logical errors


Errors

• Compile-time errors occur during program compilation and an executable version of the program is not created.

• Run-time errors occur during program execution and cause abnormal program termination.

• Logical errors occur during program execution and produce incorrect results.


Java Syntax

• To write without syntax mistakes you have to know Java syntax.

SyntaxSyntax -

the study of the patterns of formation of sentences and phrases from words and of the rules for the formation of grammatical sentences in a language.


Java Syntax

• Case-sensitive• Semi-colon (;) is line terminator• Curly braces ({,}) used for block structure• Several keywords


Comments

There are two kinds of comments: • /* text */ A traditional comment: all the text from

the ASCII characters /* to the ASCII characters */ is ignored.

• // text An end-of-line comment: all the text from the ASCII characters // to the end of the line is ignored.


Comments

Comments do not nest. • /* and */ have no special meaning in comments

that begin with //. • // has no special meaning in comments that begin

with /* or /**.

As a result, the text: /* this comment /* // /** ends here: */is a single complete comment.


Identifiers

An identifier is:an unlimited-length sequence of Java letters

and Java digits, the first of which must be a Java letter.

An identifier cannot have the same spelling (Unicode character sequence) as:

• a keyword, • boolean literal, • the null literal


Unicode

• Letters and digits may be drawn from the entire Unicode character set (The character set that uses 16 bit per character).

• Identifier can be written in most writing scripts in use in the world today, including:

Hebrew,Chinese, Japanese, KoreanPractically all languages


Identifiers examples

• Uppercase and lowercase are different.

All the following are different identifiers:

MY my My mY my1

Examples of identifiers are:

String i3

isLetterOrDigit מונה

MAX_VALUE


KeywordsThe following are reserved words called keywords

and cannot be used as identifiers:

abstractbooleanbreakbytebyvaluecasecastcatchcharclassconstcontinue

defaultdodoubleelseextendsfalsefinalfinallyfloatforfuturegeneric

gotoifimplementsimportinnerinstanceofintinterfacelongnativenewnull

operatorouterpackageprivateprotectedpublicrestreturnshortstaticsuperswitch

synchronizedthisthrowthrowstransienttruetryvarvoidvolatilewhile


True, False, Null

While true and false might appear to be keywords, they are technically Boolean literals.

Similarly, while null might appear to be a keyword, it is technically the null literal.


Literals A literal is a source code representation of a value of:

• a primitive type,• the String type,• the null type

Kinds of Literals: IntegerLiteral FloatingPointLiteral

BooleanLiteral CharacterLiteralStringLiteralNullLiteral


Integer Literals

An integer literal may be expressed in:• decimal (base 10), • hexadecimal (base 16), • octal (base 8)


Hexadecimal numeral

• A hexadecimal numeral consists of the leading characters 0x or 0X followed by one or more hexadecimal digits.

• It can represent a positive, zero, or negative integer. • Hexadecimal digits with values 10 through 15 are

represented by the letters a through f or A through F, respectively.

HexDigit is one of:

0 1 2 3 4 5 6 7 8 9 a b c d e f A B C D E F


Octal numeral

• An octal numeral consists of a digit 0 followed by one or more of the digits 0 through 7.

• It can represent a positive, zero, or negative integer.

• Octal numerals always consist of two or more digits.


Example

Examples of int literals:

02 0372

0xDadaCafe 1996

0x00FF00FF • the same number in decimal octal hexadecimal:

3 03 0x3

15 017 0xF


Zero

• 0 is always considered to be a decimal numeral.• The numerals 0, 00, and 0x0 all represent exactly

the same integer value – zero value.


Floating-Point Literals• A floating-point literal has the following parts:

• a whole-number part, • a decimal point (represented by an ASCII period character), • a fractional part, • an exponent (is indicated by a letter e or E followed by an

optionally signed integer),

• and a type suffix. • At least one digit, in either the whole number or

the fraction part, and either a decimal point, an exponent, or a float type suffix are required. All other parts are optional.


Floating-Point Literals

• A floating-point literal is of type float if it is suffixed with an ASCII letter F or f; otherwise its type is double and it can optionally be suffixed with an ASCII letter D or d.

Examples of float literals:

1e1f 2.f .3f 0f 3.14f 6.022137e+23f

Examples of double literals:

1e12..30.03.14


Boolean Literals

• The boolean type has two values, represented by the literals true and false

• A boolean literal is always of type boolean.

BooleanLiteral is one of:

true false


Character Literals

• A character literal is expressed as a character or an escape sequence, enclosed in single quotes.

• The single-quote, or apostrophe, character is \u0027 - .

• A character literal is always of type char.

Examples of char literals:

'a‘ '%‘ '\t‘ '\\‘ '\u03a9‘

'\uFFFF‘ '\177'


Unicode Character Type

•A char value stores a single character from the Unicode character set.

•The values range is between 0 and 65535.

•The amount of memory it requires: 16 bit or 2 bytes.

•The Unicode character set uses 16 bits per character.


Part of the Unicode Set0x3041 …

0x05B0 …

0x77CD …

0x0021 …

…


ASCII

• The ASCII character set is still the basis for many other programming languages.

• The ASCII character set uses 8 bits (one byte) per character.

• ASCII is a subset of Unicode.


Part of the ASCII Set

0x21 …

…0xB9


String Literals • A string literal consists of zero or more characters

enclosed in double quotes. • A string literal is always of type String.

Examples of string literals: "" // the empty string

"This is a string" // a string containing 16 characters

"This is a " + // actually a string-valued constant expression,

"two-line string" // formed from two string literals


Escape Sequences for Character and String Literals

• The character and string escape sequences allow for the representation of some non-graphic characters as well as the single quote, double quote, and backslash characters in character literals and string literals.


Escape Sequences for Character and String Literals

Escape Sequence:\ b /* \u0008: backspace BS */\ t /* \u0009: horizontal tab HT */\ n /* \u000a: linefeed LF */\ f /* \u000c: form feed FF */\ r /* \u000d: carriage return CR */\ " /* \u0022: double quote " */\ ' /* \u0027: single quote ' */\ \ /* \u005c: backslash \ */


The Null Literal

• The null type has one value, the null reference, represented by the literal null, which is formed from ASCII characters.

• A null literal is always of the null type.


Separators

The following nine ASCII characters are the separators (punctuators):

( ) { } [ ] ; , .


Operators

The following 37 tokens are the operators, formed from ASCII characters:

= > < ! ~ ? :

== <= >= != && || ++

-- + - * / & |

^ % << >> >>> += -=

*= /= &= |= ^= %=


Programming style

• Java is a free-format language. • There are no syntax rules about how the program

has to be arranged on a page. You can write entire program in one line.

• But as a matter of good programming style, you should lay out your program on the page in a way that will make its structure as clear as possible.


Programming style

• Some advises:• Put one statement per line. • Use indentation to indicate statements that

are contained inside control structures. • Write comments.• Give your variables names that make sense.


Style ExampleBad:

public class

Stam

{ public static void

main(String args[]){System.out.println("Hello!“);}}

Better:

// style example – outputs “Hello!”

public class Hello

{

public static void main(String args[])

{

System.out.println("Hello!");

}

}


Any Questions?

system development with java lecture 2. rina zviel-girshin @asc2 errors a program can have three...

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